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LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA
The Gale encyclopedia of neurological disorders / Stacey L. Chamberlin, Brigham Narins, editors.
p. ; cm.
Includes bibliographical references and index. ISBN 0-7876-9150-X (set hardcover : alk. paper) — ISBN 0-7876-9151-8 (v. 1) — ISBN
0-7876-9152-6 (v. 2)
1. Neurology—Encyclopedias.
[DNLM: 1. Nervous System Diseases—Encyclopedias—English. 2. Nervous System Diseases—Popular Works. WL 13 G151 2005] I. Title: Encyclopedia of neurological disorders. II. Chamberlin, Stacey L. III. Narins, Brigham, 1962– IV. Gale Group. RC334.G34 2005
CONTENTS
List of Entries ...vii
Introduction ...xiii
Advisory Board...xv
Contributors ...xvii
Entries
Volume 1: A–L...1Volume 2: M–Z...511
Glossary ...941
LIST OF ENTRIES
Agenesis of the corpus callosum Agnosia
Attention deficit hyperactivity disorder Brain and spinal tumors Brown-Séquard syndrome
Central nervous system stimulants Central pain syndrome
Cytomegalic inclusion body disease
❙
D
Electroencephalography
Lee Silverman voice treatment Leigh disease
Polymyositis Pompe disease Porencephaly
Positron emission tomography (PET) Post-polio Syndrome
Primary lateral sclerosis Primidone
Prion diseases Progressive multifocal
leukoencephalopathy Progressive supranuclear palsy Pseudobulbar palsy
Pseudotumor cerebri
❙
R
Radiation Radiculopathy
Ramsay-Hunt syndrome type II Rasmussen’s encephalitis Reflex sympathetic dystrophy Refsum disease
Repetitive motion disorders Respite
Restless legs syndrome Rett syndrome Reye syndrome
❙
S
Sandhoff disease Schilder’s disease Schizencephaly Schizophrenia Sciatic neuropathy Sciatica
Seizures
Septo-optic dysplasia Shaken baby syndrome Shingles
Single Proton Emission Computed Tomography
Sixth nerve palsy
Sjogren-Larsson Syndrome Sleep apnea
Social workers Sodium oxybate Sotos syndrome Spasticity Speech synthesizer Spina bifida
Spinal cord infarction Spinal cord injury Spinal muscular atrophy Spinocerebellar ataxia Status epilepticus Stiff person syndrome Striatonigral degeneration Stroke
Sturge-Weber syndrome Stuttering
Subacute sclerosing panencephalitis Subdural hematoma
Succinamides Swallowing disorders Sydenham’s chorea Syringomyelia
❙
T
Tabes dorsalis Tay-Sachs disease Temporal arteritis Temporal lobe epilepsy Tethered spinal cord syndrome Third nerve palsy
Thoracic outlet syndrome Thyrotoxic myopathy Tiagabine
Todd’s paralysis Topiramate Tourette syndrome Transient global amnesia Transient ischemic attack Transverse myelitis Traumatic brain injury
Tremors
Trigeminal neuralgia Tropical spastic paraparesis Tuberous sclerosis
❙
U
Ulnar neuropathy Ultrasonography
❙
V
Valproic acid and divalproex sodium
Vasculitic neuropathy Vasculitis
Ventilatory assistance devices Ventricular shunt
Ventricular system Vertebrobasilar disease Vestibular schwannoma Visual disturbances
Vitamin/nutritional deficiency Von Hippel-Lindau disease
❙
W
Wallenberg syndrome West Nile virus infection Whiplash
Whipple’s Disease Williams syndrome Wilson disease
❙
Z
Zellweger syndrome Zonisamide
PLEASE READ—IMPORTANT INFORMATION
The Gale Encyclopedia of Neurological Disordersis a medical reference product designed to inform and edu-cate readers about a wide variety of diseases, syndromes, drugs, treatments, therapies, and diagnostic equipment. Thomson Gale believes the product to be comprehensive, but not necessarily definitive. It is intended to supplement, not replace, consultation with a physician or other health-care practitioner. While Thomson Gale has made sub-stantial efforts to provide information that is accurate,
INTRODUCTION
The Gale Encyclopedia of Neurological Disorders
(GEND) is a one-stop source for medical information that covers diseases, syndromes, drugs, treatments, therapies, and diagnostic equipment. It keeps medical jargon to a minimum, making it easier for the layperson to use. The
Gale Encyclopedia of Neurological Disorderspresents au-thoritative and balanced information and is more compre-hensive than single-volume family medical guides.
SCOPE
Almost 400 full-length articles are included in The
Gale Encyclopedia of Neurological Disorders. Articles follow a standardized format that provides information at a glance. Rubrics include:
Diseases
• Definition
• Description
• Demographics
• Causes and symptoms
• Diagnosis
• Treatment team
• Treatment
• Recovery and rehabilitation
• Clinical trials
• Prognosis
• Special concerns
• Resources
• Key terms
Drugs
• Definition
• Purpose
• Description
• Recommended dosage
• Precautions
• Side effects
• Interactions
• Resources
• Key terms
Treatments
• Definition
• Purpose
• Precautions
• Description
• Preparation
• Aftercare
• Risks
• Normal results
• Resources
• Key terms
INCLUSION CRITERIA
A preliminary topic list was compiled from a wide va-riety of sources, including professional medical guides, consumer guides, and textbooks and encyclopedias. The advisory board, made up of seven medical and healthcare experts, evaluated the topics and made suggestions for in-clusion. Final selection of topics to include was made by the medical advisors in conjunction with Gale editors.
ABOUT THE CONTRIBUTORS
HOW TO USE THIS BOOK
The Gale Encyclopedia of Neurological Disorders
has been designed with ready reference in mind:
• Straightalphabetical arrangementallows users to lo-cate information quickly.
• Bold faced terms function as print hyperlinks that point the reader to full-length entries in the encyclopedia.
• A list of key termsis provided where appropriate to de-fine unfamiliar words or concepts used within the con-text of the essay.
•Cross-referencesplaced throughout the encyclopedia di-rect readers to where information on subjects without their own entries can be found. Cross-references are also used to assist readers looking for information on diseases that are now known by other names; for example, there is a
cross-reference for the rare childhood disease commonly known as HallervordSpatz disease that points to the entry en-titled Pantothenate kinase-associated neurodegeneration.
• A Resourcessection directs users to sources of further information, which include books, periodicals, websites, and organizations.
• A glossaryis included to help readers understand unfa-miliar terms.
• A comprehensive general indexallows users to easily target detailed aspects of any topic.
GRAPHICS
The Gale Encyclopedia of Neurological Disorders is enhanced with over 100 images, including photos, tables, and customized line drawings.
Intr
ADVISORY BOARD
Laurie Barclay, MD
Neurologist and Writer
Tampa, FL
F. James Grogan, PharmD
Pharmacist, Clinician, Writer, Editor, and Consultant
Swansea, IL
Joel C. Kahane, PhD
Professor, Director of the
Anatomical Sciences Laboratory
The School of Audiology and Speech-Language Pathology The University of Memphis Memphis, TN
Brenda Wilmoth Lerner, RN
Nurse, Writer, and Editor
London, UK
Yuen T. So, MD, PhD
Associate Professor
Clinical Neurosciences Stanford University School of
Medicine Stanford, CA
Roy Sucholeiki, MD
Professor, Director of the Comprehensive Epilepsy Program
Department of Neurology Loyola University Health System Chicago, IL
Gil I. Wolfe, MD
Associate Professor
Department of Neurology The University of Texas
Southwestern Medical Center Dallas, TX
CONTRIBUTORS
Lisa Maria Andres, MS, CGC
Certified Genetic Counselor and Medical Writer
San Jose, CA
Paul Arthur
Science writer
London, England
Bruno Verbeno Azevedo
Espirito Santo University Vitória, Brazil
Deepti Babu, MS, CGC
Genetic Counselor
Marshfield Clinic Marshfield, WI
Laurie Barclay, MD
Neurologist and writer
Tampa, FL
Julia Barrett
Science Writer
Madison, WI
Danielle Barry, MS
Graduate Assisstant
Center of Alcohol Studies Rutgers University Piscataway, NJ
Maria Basile, PhD
Medical Writer
Roselle, NJ
Tanja Bekhuis, PhD
Science Writer and Psychologist
TCB Research Boalsburg, PA
Juli M. Berwald, PhD
Geologist (Ocean Sciences)
Chicago, Illinois
Robert G. Best, PhD
Director
Division of Genetics
University of South Carolina School of Medicine
Columbia, SC
Michelle Lee Brandt
Medical Writer
San Francisco, CA
Dawn J. Cardeiro, MS, CGC
Genetic Counselor
Fairfield, PA
Francisco de Paula Careta
Espirito Santo University Vitória, Brazil
Rosalyn Carson-DeWitt, MD
Physician and Medical Writer
Durham, NC
Stacey L. Chamberlin
Science Writer and Editor
Fairfax, VA
Bryan Richard Cobb, PhD
Institute for Molecular and Human Genetics
Georgetown University Washington, D.C.
Adam J. Cohen, MD
Craniofacial Surgery, Eyelid and Facial Plastic Surgery, Neuro-Ophthalmology
Downers Grove, IL
Tish Davidson, AM
Medical Writer
Fremont, CA
James Paul Dworkin, PhD
Professor
Department of Otolaryngology, Voice/Speech Pathology Program and Laboratory Wayne State University Detroit, MI
L. Fleming Fallon, Jr., MD, DrPH
Professor
Department of Public Health Bowling Green State University Bowling Green, OH
Antonio Farina, MD, PhD
Department of Embryology, Obstetrics, and Gynecology University of Bologna
Bologna, Italy
Kevin Fitzgerald
Science Writer and Journalist
South Windsor, CT
Paula Anne Ford-Martin
Medical Writer
Warwick, RI
Lisa A. Fratt
Medical Writer
Ashland, WI
Rebecca J. Frey, PhD
Freelance Medical Writer
New Haven, CT
Sandra L. Friedrich, MA
Science Writer
Clinical Psychology Chicago, IL
Sandra Galeotti, MS
Science Writer
Larry Gilman, PhD
Electrical Engineer and Science Writer
Sharon, VT
Laith Farid Gulli, MD
Consulting Psychotherapist
Lathrup Village, MI
Stephen John Hage, AAAS, RT(R), FAHRA
Medical Writer
Chatsworth, CA
Brook Ellen Hall, PhD
Science Writer
Loomis, CA
Dan Harvey
Medical Writer
Wilmington, DE
Hannah M. Hoag, MSc
Science and Medical Writer
Montreal, Canada
Brian Douglas Hoyle, PhD
Microbiologist
Nova Scotia, Canada
Cindy L. Hunter, CGC
Genetic Counselor
Medical Genetics Department Indiana University School of
Medicine Indianapolis, IN
Alexander I. Ioffe, PhD
Senior Scientist
Geological Institute of the Russian Academy of Sciences
Moscow, Russia
Holly Ann Ishmael, MS, CGC
Genetic Counselor
The Children’s Mercy Hospital Kansas City, MO
Joel C. Kahane, PhD
Professor, Director of the Anatomical Sciences Laboratory
The School of Audiology and Speech-Language Pathology The University of Memphis Memphis, TN
Kelly Karpa, PhD, RPh
Assistant Professor
Department of Pharmacology Pennsylvania State University
College of Medicine Hershey, PA
Karen M. Krajewski, MS, CGC
Genetic Counselor, Assistant Professor of Neurology
Wayne State University Detroit, MI
Judy Leaver, MA
Behavioral Health Writer and Consultant
Washington, D.C.
Adrienne Wilmoth Lerner
University of Tennessee College of Law
Knoxville, TN
Brenda Wilmoth Lerner, RN
Nurse, Writer, and Editor
London, UK
Department of Microbiology and Parasitology
University of Queensland Brisbane, Australia
Peter T. Lin, MD
Research Assistant
Member: American Academy of Neurology, American
Association of Electrodiagnostic Medicine
Department of Biomagnetic Imaging
University of California, San Francisco
Foster City, CA
Iuri Drumond Louro, MD, PhD
Adjunct Professor
Human and Molecular Genetics Espirito Santo University Vitória, Brazil
Nicole Mallory, MS, PA-C
Medical Student
Wayne State University Detroit, MI
Igor Medica, MD, PhD
Assistant Professor
School of Medicine University of Rijeka Pula, Croatia
Michael Mooney, MA, CAC
Consultant Psychotherapist
Warren, MI
Alfredo Mori, MD, FACEM, FFAEM
Emergency Physician
The Alfred Hospital Victoria, Australia
Oxford’s Program in Evidence-Based Health Care
University of Oxford Oxford, England
Marcos do Carmo Oyama
Espirito Santo University Vitória, Brazil
Greiciane Gaburro Paneto
Espirito Santo University Vitória, Brazil
Borut Peterlin, MD, PhD
Neurologist; Consultant Clinical Geneticist; Director
Division of Medical Genetics University Medical Center Lubiana, Slovenia
Toni I. Pollin, MS, CGC
Research Analyst
Division of Endocrinology, Diabetes, and Nutrition University of Maryland School of
Medicine Baltimore, MD
J. Ricker Polsdorfer, MD
Medical Writer
Phoenix, AZ
Scott J. Polzin, MS, CGC
Robert Ramirez, DO
Medical Student
University of Medicine and Dentistry of New Jersey Stratford, NJ
Richard Robinson
Medical Writer
Tucson, AZ
Jennifer Ann Roggenbuck, MS, CGC
Genetic Counselor
Hennepin County Medical Center Minneapolis, MN
Nancy Ross-Flanigan
Science Writer
Belleville, MI
Stephanie Dionne Sherk
Freelance Medical Writer
University of Michigan Ann Arbor, MI
Lee Alan Shratter, MD
Consulting Radiologist
Kentfield, CA
Genevieve T. Slomski, PhD
Medical Writer
New Britain, CT
Amie Stanley, MS
Genetic Counselor
Medical Genetics The Cleveland Clinic Cleveland, OH
Constance K. Stein, PhD
Director of Cytogenetics, Assistant Director of Molecular
Diagnostics
SUNY Upstate Medical University Syracuse, NY
Roger E. Stevenson, MD
Senior Clinical Geneticist, Senior Clinical Laboratory Geneticist
Greenwood Genetic Center Greenwood, SC
Roy Sucholeiki, MD
Professor, Director of the Comprehensive Epilepsy Program
Department of Neurology Loyola University Health System Chicago, IL
Kevin M. Sweet, MS, CGC
Cancer Genetic Counselor
James Cancer Hospital, Ohio State University
Columbus, OH
David Tulloch
Science Writer
Wellington, New Zealand
Carol A. Turkington
Medical Writer
Lancaster, PA
Samuel D. Uretsky, PharmD
Medical Writer
Wantagh, NY
Chitra Venkatasubramanian, MBBS, MD (internal medicine)
Resident in Neurology
Department of Neurology and Neurosciences
Stanford University Stanford, CA.
Bruno Marcos Verbeno
Espirito Santo University Vitória, Brazil
Beatriz Alves Vianna
Espirito Santo University Vitória, Brazil
A
M
❙
Machado-Joseph disease
Definition
Machado-Joseph disease (MJD), also known as spin-ocerebellar ataxiaType 3 (SCA 3), is a rare hereditary disorder affecting thecentral nervous system, especially the areas responsible for movement coordination of limbs, facial muscles, and eyes. The disease involves the slow and progressive degeneration of brain areas involved in motor coordination, such as the cerebellar, extrapyramidal, py-ramidal, and motor areas. Ultimately, MJD leads to paral-ysis or a crippling condition, although intellectual functions usually remain normal. Other names of MJD are Portuguese-Azorean disease, Joseph disease, Azorean disease.
Description
Machado-Joseph disease was first described in 1972 among the descendants of Portuguese-Azorean immi-grants to the United States, including the family of William Machado. In spite of differences in symptoms and degrees of neurological degeneration and movement im-pairment among the affected individuals, it was suggested by investigators that in at least four studied families the same gene mutation was present. In early 1976, investi-gators went to the Azores Archipelago to study an existing neurodegenerative disease in the islands of Flores and São Miguel. In a group of 15 families, they found 40 people with neurological disorders with a variety of different symptoms among the affected individuals.
Another research team in 1976 reported an inherited neurological disorder of the motor system in Portuguese families, which they named Joseph disease. During the same year, the two groups of scientists both published in-dependent evidence suggesting that the same disease was the primary cause for the variety of symptoms observed. When additional reports from other countries and ethnic groups were associated with the same inherited disorder, it was initially thought that Portuguese-Azorean sailors
had been the probable disseminators of MJD to other pop-ulations around the world during the sixteenth century pe-riod of Portuguese colonial explorations and commerce. Presently, MJD is found in Brazil, United States, Portugal, Macau, Finland, Canada, Mexico, Israel, Syria, Turkey, Angola, India, United Kingdom, Australia, Japan, and China. Because MJD continues to be diagnosed in a vari-ety of countries and ethnic groups, there are current doubts about its exclusive Portuguese-Azorean origin.
Causes and symptoms
The gene responsible for MJD appears at chromo-some 14, and the first symptoms usually appear in early adolescence. Dystonia (spasticity or involuntary and repetitive movements) or gait ataxiais usually the initial symptoms in children. Gait ataxia is characterized by un-stable walk and standing, which slowly progresses with the appearance of some of the other symptoms, such as hand dysmetria, involuntary eye movements, loss of hand and superior limbs coordination, and facial dystonia (ab-normal muscle tone). Another characteristic of MJD is clinical anticipation, which means that in most families the onset of the disease occurs progressively earlier from one generation to the next. Among members of the same fam-ily, some patients may show a predominance of muscle tone disorders, others may present loss of coordination, some may have bulging eyes, and yet another sibling may be free of symptoms during his/her entire life. In the late stages of MJD, some people may experience deliriumor
dementia.
Mac
hado-J
oseph disease
Key Terms
Autosomal Relating to any chromosome besides
the X and Y sex chromosomes. Human cells con-tain 22 pairs of autosomes and one pair of sex chro-mosomes.
Cerebellar Involving the part of the brain (cere-bellum) that controls walking, balance, and coor-dination.
Dysarthria Slurred speech.
Dystonia Painful involuntary muscle cramps or spasms.
Extrapyramidal Refers to brain structures located outside the pyramidal tracts of the central nervous system.
Genotype The genetic makeup of an organism or a set of organisms.
Mutation A permanent change in the genetic ma-terial that may alter a trait or characteristic of an in-dividual, or manifest as disease. This change can be transmitted to offspring.
Penetrance The degree to which individuals pos-sessing a particular genetic mutation express the trait that this mutation causes. One hundred per-cent penetrance is expected to be observed in truly dominant traits.
Phenotype The physical expression of an individ-ual’s genes.
Spasticity Increased mucle tone, or stiffness, which leads to uncontrolled, awkward move-ments.
Trinucleotide A sequence of three nucleotides.
the opposite area of the brain to the arms and legs. Pyra-midal tract nerves regulate both voluntary and reflex mus-cle movements. However, as the disease progresses, both motor systems tracks will eventually suffer degeneration.
Diagnosis
Diagnosis depends mainly on the clinical history of the family. Genetic screening for the specific mutation that causes MJD can be useful in cases of persons at risk or when the family history is not known or a person has symptoms that raise suspicion of MJD. Initial diagnosis may be difficult, as people present symptoms easily mis-taken for other neurological disorders such as Parkinson
and Huntington diseases, or even multiple sclerosis.
Treatment
Although there is no cure for Machado-Joseph dis-ease, some symptoms can be relieved, The medication Levodopa or L-dopa often succeeds in lessening muscle rigidity and tremors, and is often given in conjunction with the drug Carbidopa. However, as the disease pro-gresses and the number of neurons decreases, this pallia-tive (given for comfort) treatment becomes less effecpallia-tive. Antispasmodic drugs such as baclofen are also prescribed to reduce spasticity. Dysarthria, or difficulty to speak, and dysphagia, difficulty to swallow, can be treated with proper medication and speech therapy. Physical therapy can help patients with unsteady gait, and walkers and wheelchairs may be needed as the disease progresses. Other symptoms also require palliative treatment, such as muscle cramps, urinary disorders, and sleep problems.
Clinical Trials
Further basic research is needed before clinical trials
become a possibility for MJD. Ongoing genetic and mo-lecular research on the mechanisms involved in the genetic mutations responsible for the disease will eventually yield enough data to provide for future development and design of experimental gene therapies and drugs specific to treat those with MJD.
Prognosis
The frequency with which such genetic mutations trigger the clinical onset of disease is known as trance. Machado-Joseph disease presents a 94.5% pene-trance, which means that 94.5% of the mutation carriers will develop the symptoms during their lives, and less than 5% will remain free of symptoms. Because the intensity and range of symptoms are highly variable among the af-fected individuals, it is difficult to determine the progno-sis for a given individual. As MJD progresses slowly, most patients survive until middle age or older.
Resources BOOKS
Fenichel, Gerald M. Clinical Pediatric Neurology: A Signs and Symptoms Approach,4th ed. Philadelphia: W. B. Saunders Company, 2001.
OTHER
National Institute of Neurological Disorders and Stroke.
Machado-Joseph Disease Fact Sheet.May 5, 2003 (June 7, 2004). <http://www.ninds.nih.gov/ health_and_medical/pubs/machado-joseph.htm>.
ORGANIZATIONS
Magnetic r
esonance imaging (MRI)
Technician conducting an MRI. (Will & Deni McIntyre/Photo Researchers, Inc. Reproduced by permission.)
International Machado-Joseph Disease Foundation, Inc. P.O. Box 994268, Redding, CA 96099-4268. (530) 246-4722. MJD@ijdf.net. <http://www.ijdf.net>.
National Ataxia Foundation (NAF). 2600 Fernbrook Lane, Suite 119, Minneapolis, MN 55447-4752. (763) 553-0020; Fax: (763) 553-0167. naf@ataxia.org. <http://www.ataxia.org>.
National Organization for Rare Disorders (NORD). P.O. Box 1968 (55 Kenosia Avenue), Danbury, CT 06813-1968. (203) 744-0100 or (800) 999-NORD (6673); Fax: (203) 798-2291. orphan@rarediseases.org. <http://www. rarediseases.org>.
Worldwide Education & Awareness for Movement Disorders (WE MOVE). 204 West 84th Street, New York, NY 10024. (212) 875-8312 or (800) 437-MOV2 (6682); Fax: (212) 875-8389. wemove@wemove.org. <http://www.wemove.org>.
Sandra Galeotti
Macrencephaly
see
Megalencephaly
Mad cow disease
see
Creutzfeldt-Jakob
disease
❙
Magnetic resonance imaging
(MRI)
Definition
Magnetic resonance imaging (MRI) scanners rely on the principles of atomic nuclear-spin resonance. Using strong magnetic fields and radio waves, MRI collects and correlates deflections caused by atoms into images. MRIs (magnetic resonance imaging tests) offer relatively sharp pictures and allow physicians to see internal bodily struc-tures with great detail. Using MRI technology, physicians are increasingly able to make diagnosis of serious pathol-ogy (e.g., tumors) earlier, and earlier diagnosis often trans-lates to a more favorable outcome for the patient.
Description
A varying (gradient) magnetic field exists in tissues in the body that can be used to produce an image of the tis-sue. The development of MRI was one of several powerful diagnostic imaging techniques that revolutionized medi-cine by allowing physicians to explore bodily structures and functions with a minimum of invasion to the patient. In the last half of the twentieth century, dramatic ad-vances in computer technologies, especially the develop-ment of mathematical algorithms powerful enough to allow difficult equations to be solved quickly, allowed
MRI to develop into an important diagnostic clinical tool. In particular, the ability of computer programs to eliminate “noise” (unwanted data) from sensitive measurements en-hanced the development of accurate, accessible and rela-tively inexpensive noninvasive technologies.
Nuclear medicine is based upon the physics of excited atomic nuclei. Nuclear magnetic resonance (NMR) was one such early form of nuclear spectroscopy that eventu-ally found widespread use in clinical laboratory and med-ical imaging. Because a proton in a magnetic field has two quantized spin states, NMR allowed the determination of the complex structure of organic molecules and, ulti-mately, the generation of pictures representing the larger structures of molecules and compounds (such as neural tissue, muscles, organs, bones, etc.). These pictures were obtained as a result of measuring differences between the expected and actual numbers of photons absorbed by a tar-get tissue.
Megalencephal
y
Key Terms
Magnetic resonance imaging MRI An imaging
technique used in evaluation and diagnoses of the brain and other parts of the body.
Resonance A condition in which the applied
force (e.g., forced vibrations, forced magnetic field, etc.) becomes the same as the natural fre-quency of the target (e.g., tissue, cell structure, etc.).
became the physical and chemical basis of the powerful diagnostic technique of MRI.
The resolution of MRI scanning is so high that they can be used to observe the individual plaques inmultiple sclerosis. In a clinical setting, a patient is exposed to short bursts of powerful magnetic fields and radio waves from electromagnets. MRI images do not utilize potentially harmful ionizing radiation generated by three-dimensional x-ray computed tomography (CT) scans, and there are no known harmful side effects. The magnetic and radio wave bursts stimulate signals from hydrogen atoms in the pa-tient’s tissues that, when subjected to computer analysis, create a cross-sectional image of internal structures and organs.
Healthy and diseased tissues produce different signal patterns and thus allow physicians to identify diseases and disorders.
American chemist and physicist Paul Lauterbur and British physicist Sir Peter Mansfield shared the 2003 Nobel Prize in Physiology or Medicine for their discover-ies concerning the use of magnetic resonance to visualize different structures.
MRI tests, brain scans, and potential security issues
Studies of the potential of new brain wave scanners explore the possibility that MRI tests could be part of a more accurate form of polygraph (lie detector). Current polygraphs are of debatable accuracy (usually they are not admissible in court as evidence) and measure observable fluctuations in heart rate, breathing, perspiration, etc.
In a 2001 University of Pennsylvania experiment using MRI, 18 subjects were given objects to hide in their pockets, then shown a series of pictures and asked to deny that the object depicted was in their pockets. Included was a picture of the object they had pocketed and so subjects were “lying” (making a deliberate false statement) if they claimed that the object was not in their pocket. An MRI recorded an increase of activity in the anterior cinglate, a portion of the brain associated with inhibition of responses and monitoring of errors, as well as the right superior frontal gyrus, which is involved in the process of paying attention to particular stimuli.
After the September 11, 2001, terrorist attacks, a number of government agencies in the United States began to take a new look at brain scanning technology as a po-tential means of security screening. Such activity, along with an increase of interest in potential brain-wave scan-ning by the Federal Bureau of Investigation (FBI), has raised concerns among civil-liberties groups, which view brain-wave scanning as a particularly objectionable inva-sion of privacy.
Resources PERIODICALS
Young, Emma. “Brain Scans Can Reveal Liars.”New Scientist
(November 12, 2001).
WEBSITES
Hornak, J. P. The Basics of MRI.May 9, 2004 (June 2, 2004). <http://www.cis.rit.edu/htbooks/mri/>.
Johnson, K. A., and J. A. Becker. The Whole Brain Atlas.May 9, 2004 (June 2, 2004). <http://www.med.harvard.edu/ AANLIB/home.html>.
Paul Arthur
❙
Megalencephaly
Definition
Megalencephaly (also called macrencephaly) de-scribes an enlarged brain whose weight exceeds the mean (the average weight for that age and sex) by at least 2.5 standard deviations (a statistical measure of variation). Megalencephaly may also be defined in terms of volume rather than weight. Hemimegalencephaly (or unilateral megalencephaly) is a related condition in which brain en-largement occurs in one hemisphere (half) of the brain.
Description
A person with megalencephaly has a large, heavy brain. In general, a brain that weighs more than 1600 grams (about 3.5 pounds) is considered megalencephalic. The heaviest brain on record weighed 2850 grams (about 6.3 pounds). Macrocephaly, a related condition, refers to an abnormally large head. Macrocephaly may be due to megalencephaly or other causes such as hydrocephalus
Megalencephal
y
Key Terms
Autosomal dominant A pattern of inheritance in which only one of the two copies of an autosomal gene must be abnormal for a genetic condition or disease to occur. An autosomal gene is a gene that is located on one of the autosomes or non-sex chro-mosomes. A person with an autosomal dominant dis-order has a 50% chance of passing it to each of their offspring.
Autosomal recessive A pattern of inheritance in which both copies of an autosomal gene must be ab-normal for a genetic condition or disease to occur. An autosomal gene is a gene that is located on one of the autosomes or non-sex chromosomes. When both parents have one abnormal copy of the same gene, they have a 25% chance with each pregnancy that their offspring will have the disorder.
Chromosome A microscopic thread-like structure found within each cell of the human body and
con-sisting of a complex of proteins and DNA. Humans have 46 chromosomes arranged into 23 pairs. Chro-mosomes contain the genetic information necessary to direct the development and functioning of all cells and systems in the body. They pass on hereditary traits from parents to child (like eye color) and de-termine whether the child will be male or female. Gene A building block of inheritance, which con-tains the instructions for the production of a particu-lar protein, and is made up of a molecuparticu-lar sequence found on a section of DNA. Each gene is found on a precise location on a chromosome.
Inborn error of metabolism One of a group of rare conditions characterized by an inherited defect in an enzyme or other protein. Inborn errors of metabolism can cause brain damage and mental retardation if left untreated. Phenylketonuria, Tay-Sachs disease, and galactosemia are inborn errors of metabolism.
problems or birth defects of the body). Dysmorphic facial features (abnormal shape, position or size of facial fea-tures) may also be observed in an affected individual.
According to the National Institute of Neurological Disorders and Stroke (NINDS), megalencephaly is one of the cephalic disorders, congenital conditions due to dam-age to or abnormal development of the nervous system. There have been various attempts to classify megalen-cephaly into subcategories based on etiology (cause) and/or pathology (the condition of the brain tissue and cells). Dekaban and Sakurgawa (1977) proposed three main categories: primary megalencephaly, secondary megalencephaly, and hemimegalencephaly. DeMyer (1986) proposed two main categories: anatomic and meta-bolic. Gooskens and others (1988) modified these classi-fications and added a third category: dynamic megalencephaly. The existence of different classification systems highlights the inherent difficulty in categorizing a condition that has a wide range of causes and associated pathology.
Demographics
The incidence of megalencephaly is estimated at be-tween 2% and 6%. There is a preponderance of affected males; megalencephaly affects males three to four times more often than it does females. Among individuals with macrocephaly, estimates of megalencephaly are between 10 and 30%. Hemimegalencephaly is a rare condition and occurs less frequently than megalencephaly.
Causes and symptoms
Both genetic and non-genetic factors may produce megalencephaly. Most often, megalencephaly is a familial trait that occurs without extraneural (outside the brain) findings. Familial megalencephaly may occur as an auto-somal dominant (more common) or autoauto-somal recessive condition. The autosomal recessive form is more likely than the autosomal dominant form to result in mental re-tardation. Other genetic causes for megalencephaly in-clude single gene disorders such as Sotos syndrome(an overgrowth syndrome),neurofibromatosis(a neurocuta-neous syndrome), and Alexander disease(a leukodys-trophy); or a chromosome abnormality such as Klinefelter syndrome. Non-genetic factors such as a transient disorder of cerebral spinal fluid may also contribute to the devel-opment of megalencephaly. Finally, megalencephaly can be idiopathic (due to unknown causes).
The cells that make up the brain (neurons and other supporting cells) form during the second to fourth months of pregnancy. Though the precise mechanisms behind megalencephaly at the cellular level are not fully under-stood, it is thought that the condition results from an in-creased number of cells, an inin-creased size of cells, or accumulation of a metabolic byproduct or abnormal sub-stance due to an inborn error of metabolism. It is possible that more than one of these processes may explain mega-lencephaly in a given individual.
Megalencephal
y disorder typically presents as a large head circumference
(distance around the head) either prenatally (before birth), at birth, or within the first few years of life. The head circumference may increase rapidly in the span of a few months or may progress slowly over a longer period of time. Head shape may be abnormal and skull abnor-malities such as widened or split sutures (fibrous joints be-tween the bones of the head) may occur. There may also be increased cranial pressure and bulging fontanels (the membrane covered spaces at the juncture of an infant’s cranial bones which later harden).
From a neurological standpoint, the clinical picture of megalencephaly varies widely. Manifestations may range from normal intellect, as with case of benign familial megalencephaly, to severe mental retardation and seizures, as with Alexander disease, an inherited leukodystrophy (disease of the brain’s white matter). Neurological symp-toms that may be present or develop in a person with megalencephaly include:
• delay of motor milestones such as holding up head, rolling over, or sitting
• mental retardation • speech delay • poor muscle tone • body asymmetry
• paralysis of one or both sides of the body • poor coordination
• involuntary movements • visual disturbances
Brain abnormalities that may be seen in individuals with megalencephaly include:
• gyral abnormalities • neuronal heterotopias • corpus callosum dysgenesis • myelum dysplasia
• abnormal or an excess amount of neurons • abnormal or an excess amount of glia cells
Diagnosis
A diagnosis of megalencephaly is based on clinical findings and results of brain imaging studies. Since mega-lencephaly can be a benign condition, there may well be many individuals who never come to medical attention. Though no longer used as a primary means of diagnosing megalencephaly, an autopsy may provide additional evi-dence to support this diagnosis. The evaluation of a patient with suspected megalencephaly will usually consist of questions about medical history and family history, a
physical exam that includes head measurements, and a de-velopmental and/or neurological exam. It may be neces-sary to obtain head circumference measurements for first-degree relatives (parents, siblings, children). De-pending upon the history and clinical findings, a physician may recommend imaging studies such as CT (computed tomography) scan or MRI (magnetic resonance imag-ing). Findings on CT scanor MRI consistent with a diag-nosis of megalencephaly are an enlarged brain with normal-sized ventricles and subarachnoid spaces. The vol-ume (size) of the brain may be calculated or estimated using measurements from the CT or MRI. A patient with megalencephaly may be referred to specialists in neurol-ogy or genetics for further evaluation. Laboratory testing for a genetic condition or chromosome abnormality may also be performed.
Treatment
There is no specific cure for megalencephaly. Man-agement of this condition largely depends upon the pres-ence and severity of associated neurological and physical problems. In cases of benign familial megalencephaly, ad-ditional management beyond routine health care mainte-nance may consist of periodic head measurements and patient education about the inheritance and benign nature of the condition. For patients with neurological and/or physical problems, management may include anti-epilep-tic drugs for seizures, treatment of medical complications related to the underlying syndrome, and rehabilitation for neurological problems such as speech delay, poor muscle tone, and poor coordination. Placement in a residential care facility may be necessary for those cases in which megalencephaly is accompanied by severe mental retar-dation or uncontrollable seizures.
Treatment team
The types of professionals involved in the care of pa-tients is highly individualized because the severity of symptoms varies widely from patient to patient. For pa-tients with associated neurological and/or physical prob-lems, the treatment team may include specialists in neonatology, neurology, radiology, orthopedics, rehabili-tation, and genetics. Genetic counseling may be helpful to the patient and family, especially at the time of diagnosis. Participation in a support group may also be beneficial to those families adversely affected by megalencephaly.
Recovery and rehabilitation
Melodic intonation ther
ap
y
may be indicated for individuals with megalencephaly. Early intervention services for young children and special education or other means of educational support for school-aged children may be recommended if develop-mental delays, learning disabilities, or other barriers to learning are present. The goal of these therapies is to max-imize the patient’s success in school, work, and life in gen-eral. A child with megalencephaly may be eligible to have an Individual Education Plan (IEP). An IEP provides a framework from which administrators, teachers, and par-ents can meet the educational needs of a child with learn-ing disabilities. Dependlearn-ing upon severity of symptoms and the degree of learning difficulties, some children with megalencephaly may be best served by special education classes or a private educational setting.
Clinical trials
As of 2004, there were no active clinical trials
specifically designed to study megalencephaly. Patients with underlying syndromes that produce megalencephaly may be candidates for clinical trials that relate to that par-ticular syndrome. For more information, interested indi-viduals may search for that specific condition (for example, neurofibromatosis) at www.clinicaltrails.gov.
Prognosis
The prognosis for megalencephaly varies according to the presence and severity of associated problems such as intractable seizures, paralysis, and mental retardation. Hemimegalencephaly is often associated with severe seizures, hemiparesis (paralysis of one side of the body), and mental retardation and as such, it carries a poor prog-nosis. In the case of a fetus diagnosed with megalen-cephaly, prediction of outcome remains imprecise.
Resources BOOKS
Greer, Melvin. “Structural Malformations,” Chapter 78. In
Merritt’s Textbook of Neurology, 10th edition, edited by L. P. Rowland. Baltimore, MD: Williams and Wilkins, 2000. Graham, D. I., and P. L. Lantos, eds. Greenfield’s
Neuropathology,volume I, 7th edition. London: Arnold, 2002.
Parker, James N., and Philip M. Parker, eds. The Official Parent’s Sourcebook on Alexander Disease: A Revised and Updated Directory for the Internet Age.San Diego, CA: ICON Health Publications, 2003.
PERIODICALS
Bodensteiner, J. B. and E. O. Chung. “Macrocrania and mega-lencephaly in the neonate.”Seminars on Neurology13 (March 1993): 84–91.
Cutting, L. E., K. L. Cooper, C. W. Koth, S. H. Mostofsky, W.R. Kates, M. B. Denckla, and W. E. Kaufmann. “Megalencephaly in NF1: predominantly white matter
contribution and mitigation by ADHD.”Neurology59 (November 2002): 1388–94.
DeMyer, W. “Megalencephaly: types, clinical syndromes and management.”Pediatric Neurology2 (1986): 321–28. Gooskens, R. H. J. M., J. Willemse, J. B. Bijlsma, and P.
Hanlo. “Megalencephaly: Definition and classification.”
Brain and Development10 (1988): 1–7.
Johnson, A. B., and M. Brenner. “Alexander’s disease: clinical, pathologic, and genetic features.”Journal of Child Neurology18 (September 2003): 625–32.
Singhal, B. S., J. R. Gorospe, and S. Naidu. “Megalencephalic leukoencephalopathy with subcortical cysts.”Journal of Child Neurology18 (September 2003): 646–52.
WEBSITES
The National Institute of Neurological Disorders and Stroke (NINDS). Megalencephaly Information Page.
<http://www.ninds.nih.gov/health_and_medical/ disorders/megalencephaly.htm>.
The National Institute of Neurological Disorders and Stroke (NINDS). Cephalic Disorders Fact Sheet.<http:// www.ninds.nih.gov/health_and_medical/pubs/ cephalic_disorders.htm>.
Online Mendelian Inheritance In Man (OMIM).
Megalencephaly.<http://www.ncbi.nlm.nih.gov/ entrez/dispomim.cgi?id=155350>.
ORGANIZATIONS
National Institute of Child Health and Human Development (NICHD) Information Resource Center. P. O. Box 3006, Rockville, MD 20847. (301) 496-7101 or (800) 370-2943. NICHDInformationResourceCenter@mail.nih.gov. <http://www.nichd.nih.gov>.
National Institute of Neurological Disorders and Stroke (NINDS, Brain Resources and Information Network (BRAIN). P. O. Box 5801, Bethesda, MD. (800) 352-9424. <http://www.ninds.nih.gov>.
National Organization for Rare Disorders (NORD). PO Box 1968, 55 Kensonia Avenue, Danbury, CT 06813. (203) 744-0100 or 800-999-NORD (6673); Fax: (203) 798-2291. orphan@rarediseases.org. <http://www.rare diseases.org>.
Dawn J. Cardeiro, MS, CGC
Meige syndrome
see
Hemifacial spasm
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Melodic intonation therapy
Definition
Melodic intonation ther
ap
y Purpose
Although MIT was first described in the 1970s, it is considered a relatively new and experimental therapy. Few research studies have been performed to analyze the ef-fectiveness of treatment with large numbers of patients. Despite this, some speech therapists use the method for children and adults with aphasia as well as for children with developmental apraxiaof speech.
The effectiveness of MIT derives from its use of the musical components melody and rhythm in the production of speech. A group of researchers from the University of Texas have discovered that music stimulates several dif-ferent areas in the brain, rather than just one isolated area. They also found a strong correlation between the right side of the brain that comprehends music components and the left side of the brain that comprehends language compo-nents. Because music and language structures are similar, it is suspected that by stimulating the right side of the brain, the left side will begin to make connections as well. For this reason, patients are encouraged to sing words rather than speak them in conversational tones in the early phases of MIT. Studies usingpositron emission tomography
(PET) scans have shown Broca’s area (a region in the left frontal brain controlling speech and language comprehen-sion) to be reactivated through repetition of sung words.
Precautions
Patients and caregivers should be aware that there is little research to support consistent success with MIT. The-oretically, this form of therapy has the potential to improve speech communication to a limited extent.
Description
Melodic intonation therapy was originally developed as a treatment method for speech improvements in adults with aphasia. The initial method has had several modifi-cations, mostly adaptations for use by children with apraxia. The primary structure of this therapy remains rel-atively consistent however.
There are four steps, or levels, generally outlining the path of therapy.
• Level I: The speech therapist hums short phrases in a rhythmic, singsong tone. The patient attempts to follow the rhythm and stress patterns of phrases by tapping it out. With children, the therapist uses signing while hum-ming and the child is not initially expected to participate. After a series of steps, the child gradually increases par-ticipation until they sign and hum with the therapist. • Level II: The patient begins to repeat the hummed phrases
with the assistance of the speech therapist. Children at this level are gradually weaned from therapist participation.
• Level III: For adults, this is the point where therapist par-ticipation is minimized and the patient begins to respond to questions still using rhythmic speech patterns. In chil-dren, this is the final level and the transition to normal speech begins. Sprechgesang is the technique used to transition the constant melodic pitch used up to this point with the variable pitch in normal conversational speech. • Level IV: The adult method incorporates sprechgesangat this level. More complex phrases and longer sentences are attempted.
Preparation
Preparation for MIT involves some additional re-search into the therapy and discussions with a neurologist
and a speech pathologist. It is important to have an un-derstanding of the affected brain areas. MIT is most likely to be successful for patients who meet certain criteria such as non-bilateral brain damage, good auditory aptitude, non-fluent verbal communication, and poor word repeti-tion. The speech pathologist should be familiar with the different MIT methodologies as they relate to either adults or children.
Aftercare
There is no required aftercare for MIT.
Risks
There are no physical risks associated with the use of melodic intonation therapy.
Normal results
The expected outcome after completion of the MIT sequence is increased communication through production of intelligible word groups. Patients are typically able to form short sentences of 3–5 words, but more complex communication may also be possible depending on the ini-tial cause of speech impairment.
Resources BOOKS
Aldridge, David. Music Therapy in Dementia Care. Jessica Kingsley Publishing, 2000.
PERIODICALS
Baker, Felicity A. “Modifying the Melodic Intonation Therapy Program for Adults with Severe Non-fluent Aphasia.”
Music Therapy Perspectives18, no. 2 (2000): 110–14. Belin, P., et al. “Recovery from Nonfluent Aphasia After
Melodic Intonation Therapy: A PET Study.”Neurology
47, no. 6 (December 1996): 1504–11.
Ménièr
e’
s disease
Key Terms
Aphasia Loss of the ability to use or understand language, usually as a result of brain injury or dis-ease.
Apraxia Loss of the ability to carry out a voluntary movement despite being able to demonstrate nor-mal muscle function.
Pitch The property of sound that is determined by the frequency of sound wave vibrations reaching the ear.
Patients.”Iranian Journal of Medical Sciences25 (2000): 156–60.
Helfrich-Miller, Kathleen. “A Clinical Perspective: Melodic Intonation Therapy for Developmental Apraxia.”Clinics in Communication Disorders4, no. 3 (1994): 175–82. Roper, Nicole. “Melodic Intonation Therapy with Young
Children with Apraxia.”Bridges1, no. 8 (May 2003). Sparks R, Holland A. “Method: melodic intonation therapy for
aphasia.”Journal of Speech and Hearing Disorders.
1976;41:287–297.
ORGANIZATIONS
American Speech-Language-Hearing Association. 10801 Rockville Pike, Rockville, MD 20852. (301) 897-5700 or (800) 638-8255; Fax: (301) 571-0457. action
center@asha.org. <http://www.nsastutter.org>.
Music Therapy Association of British Columbia. 2055 Purcell Way, North Vancouver, British Columbia V7J 3H5, Canada. (604) 924-0046; Fax: (604) 983-7559. info@mtabc.com. <http://www.mtabc.com>.
The Center For Music Therapy. 404-A Baylor Street, Austin, TX 78703. (512) 472-5016; Fax: (512) 472-5017. info@centerformusictherapy.com. <http://www.centerfor musictherapy.com>.
Stacey L. Chamberlin
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Ménière’s disease
Definition
Ménière’s disease is a disorder characterized by re-current vertigo, sensory hearing loss, tinnitus, and a feel-ing of fullness in the ear. It is named for the French physician, Prosper Ménière, who first described the illness in 1861. Ménière’s disease is also known as idiopathic en-dolymphatic hydrops; “idiopathic” refers to the unknown or spontaneous origin of the disorder, while “endolym-phatic hydrops” refers to the increased fluid pressure in the inner ear that causes the symptoms of Ménière’s disease.
Description
Patients with Ménière’s disease have periodic attacks characterized by four major symptoms:
• Vertigo. This is a spinning or whirling sensation that af-fects the patient’s sense of balance; it is sometimes vio-lent. The vertigo is often accompanied by nausea and vomiting.
• Fluctuating loss of hearing.
• Tinnitus. This is a sensation of ringing, buzzing, or roar-ing noises in the ear. The most common type of tinnitus associated with Ménière’s is a low-pitched roaring. • A sensation of fullness, pressure, or discomfort in the ear.
Some patients also experience headaches, diarrhea, and painin the abdomen during an attack.
Attacks usually come on suddenly and last from two or three to 24 hours, although some patients experience an aching sensation in the affected ear just before an attack. The attacks typically subside gradually. In most cases, only one ear is affected; however, 10–15% of patients with Ménière’s disease are affected in both ears. After a severe attack, the patient often feels exhausted and sleeps for sev-eral hours.
The spacing and intensity of Ménière’s attacks vary from patient to patient. Some people have several acute episodes relatively close together, while others may have one or two milder attacks per year or even several years apart. In some patients, attacks occur at regular intervals, while in others, the attacks are completely random. In some patients, acute attacks are triggered by psychologi-cal stress, menstrual cycles, or certain foods. Patients usu-ally feel normal between episodes; however, they may find that their hearing and sense of balance get slightly worse after each attack.
Demographics
The National Institute on Deafness and Other Com-munication Disorders (NIDCD) estimates that, as of 2003, there are about 620,000 persons in the United States di-agnosed with Ménière’s disease. Another expert gives a figure of 1,000 cases per 100,000 people. About 46,000 new cases are diagnosed each year; some neurologists, however, think that the disorder is underdiagnosed.
Ménière’s disease has been diagnosed in patients of all ages, although the average age at onset is 35–40 years of age. The age of patients in several controlled studies of the disorder ranged from 49 to 67 years.
Ménièr
e’
s disease
more likely than men to develop Ménière’s; various stud-ies report female-to-male ratios between 1.1:1 and 3:2. There is no evidence as of 2003 that Ménière’s dis-ease occurs more frequently in some racial or ethnic groups than in others.
Causes and symptoms
The underlying causes of Ménière’s disease are poorly understood as of late 2003. Some geneticists pro-posed in 2002 that Ménière’s disease might be caused by a mutation in the COCH gene, which is the only human gene known to be associated with inherited hearing loss related to inner ear dysfunction. In 2003, however, two groups of researchers in Japan and the United Kingdom reported that mutations in the COCH gene are not re-sponsible for Ménière’s. Other theories about the under-lying causes of Ménière’s disease that are being investigated include virus infections and environmental noise pollution.
One area of research that shows promise is the possi-ble relationship between Ménière’s disease and migraine headache. Dr. Ménière himself suggested the possibility of a link, but early studies yielded conflicting results. A rig-orous German study published in late 2002 reported that the lifetime prevalence of migraine was 56% in patients di-agnosed with Ménière’s disease as compared to 25% for controls. The researchers noted that further work is nec-essary to determine the exact nature of the relationship be-tween the two disorders.
The immediate cause of acute attacks is fluctuating pressure in a fluid inside the inner ear known as en-dolymph. The endolymph is separated from another fluid called perilymph by thin membranes containing nerves that govern hearing and balance. When the endolymph pressure increases, there is a sudden change in the rate of nerve cells firing, which leads to vertigo and a sense of fullness or discomfort inside the ear. In addition, increased endolymph pressure irritates another structure in the inner ear known as the organ of Corti, which lies inside a shell-shaped structure called the cochlea. The organ of Corti de-tects pressure impulses, which it converts to electrical impulses that travel along the auditory nerve to the brain. The organ of Corti contains four rows of hair cells that govern a person’s perception of the pitch and loudness of a sound. Increased pressure from the endolymph affects the hair cells, causing loss of hearing (particularly the abil-ity to hear low-pitched sounds) and tinnitus.
Diagnosis
Diagnosis of Ménière’s disease is a complex process requiring a number of different procedures:
• Patient history, including family history. A primary care physician will ask the patient to describe the symptoms
experienced during the attacks, their severity, the dates of recent attacks, and possible triggers.
• Physical examination. Patients often come to the doctor’s office with signs of recent vomiting; they may be pale and sweaty, with a fast pulse and higher than normal blood pressure. There may be no unusual findings during the physical examination, however, if the patient is be-tween episodes. If the doctor suspects Ménière’s disease on the basis of the patient’s personal or family history, he or she will examine the patient’s eyes for nystagmus, or rapid and involuntary movements of the eyeball. At this point, a primary care physician may refer the patient to an audiologist or other specialist for further testing. • Hearing tests. There are several different types of
hear-ing tests used to diagnose Ménière’s. The Rinne and Weber tests use a tuning fork to detect hearing loss. In Rinne’s test, the examiner holds the stem of a vibrating tuning fork first against the mastoid bone and then out-side the ear canal. A person with normal hearing or Ménière’s disease will hear the sound as louder when it is held near the outer ear; a person with conductive hear-ing loss will hear the tone as louder when the fork is touching the bone. In Weber’s test, the vibrating tuning fork is held on the midline of the forehead and the patient is asked to indicate the ear in which the sound seems louder. A person with conductive hearing loss on one side will hear the sound louder in the affected ear, while a person with Ménière’s disease will hear the sound louder in the unaffected ear. Other hearing tests measure the person’s ability to hear sounds of different pitches and volumes. These may be repeated in order to detect periodic variations in the patient’s hearing.
• Balance tests. The most common balance tests used to diagnose Ménière’s disease are the Romberg test, in which the patient is asked to stand upright and steady with eyes closed; the Fukuda test, in which the patient is asked to march in place with eyes closed; and the Dix-Hallpike test, in which the doctor moves the patient from a sitting position to lying down while holding the pa-tient’s head tilted at a 45-degree angle. Patients with Ménière’s disease tend to lose their balance or move from side to side during the first two tests. The Dix-Hallpike test is done to rule out benign paroxysmal po-sitional vertigo (BPPV), a condition caused by small crystals of calcium carbonate that have collected within a part of the inner ear called the utricle. Some patients with Ménière’s disease may have a positive score on the Dix-Hallpike test, indicating that they also have BPPV. • Blood tests. These are ordered to rule out metabolic dis-orders, autoimmune disdis-orders, anemia, leukemia, or in-fectious diseases (Lyme diseaseand neurosyphilis). • Transtympanic electrocochleography (ECoG). This test
Ménièr
e’
s disease
Key Terms
Audiologist A healthcare professional who spe-cializes in diagnostic testing of hearing impairments and rehabilitation of patients with hearing problems.
Cochlea A spiral-shaped tubular structure resem-bling a snail’s shell that forms part of the inner ear.
Conductive hearing loss A type of medically treat-able hearing loss in which the inner ear is usually normal, but there are specific problems in the mid-dle or outer ears that prevent sound from getting to the inner ear in a normal way.
Endolymph The fluid contained inside the
mem-branous labyrinth of the inner ear.
Endolymphatic hydrops Another term for Ménière’s disease. It defines the disorder in terms of increased fluid pressure in the inner ear.
Idiopathic Of unknown cause or spontaneous ori-gin. Ménière’s disease is considered an idiopathic disorder.
Labyrinth The inner ear. It consists of the membra-nous labyrinth, which is a system of sacs and ducts made of soft tissue; and the osseous or bony labyrinth, which surrounds and contains the membranous labyrinth.
Labyrinthectomy Surgical removal of the labyrinth of the ear. It is done to treat Ménière’s disease only when the patient has already suffered severe hearing loss. Mastoid bone The bony area behind and below the ear.
Nystagmus Rapid and involuntary movements of
the eyeball. Measuring and recording episodes of nystagmus is part of the differential diagnosis of Ménière’s disease.
Otolaryngology The branch of medicine that treats disorders of the ear, nose, and throat.
Otology The branch of medicine that specializes in medical or surgical treatment of ear disorders. Perilymph The fluid that lies between the membra-nous labyrinth of the inner ear and the bony labyrinth. Prophylaxis A measure taken to prevent disease or an acute attack of a chronic disorder.
Tinnitus A sensation of ringing, buzzing, roaring, or clicking noises in the ear.
Vertigo An illusory feeling that either one’s self or the environment is revolving. It is usually caused ei-ther by diseases of the inner ear or disturbances of the central nervous system.
the cochlea of the patient’s ear; it is done to detect dis-tortion of the membranes in the inner ear. ECoG is most accurate when performed during an attack of Ménière’s. • Electronystagmography (ENG). This test is done to eval-uate the functioning of the patient’s vestibular and ocu-lomotor (eye movement) systems. It takes about 60–90 minutes to complete and includes stimulating the inner ear with air or water of different temperatures as well as measuring and recording the patient’s eye movements in response to lights and similar stimuli. ENG can cause
dizzinessand nausea; patients are told to discontinue all medications for two weeks before the test and to take the test on an empty stomach.
• Imaging studies. MRIsand CT scansare done to detect abnormalities in the shape or structure of the cochlea and other parts of the inner ear, to rule out tumors, and to de-tect signs of multiple sclerosis.
Treatment team
A family care practitioner may suspect the diagnosis of Ménière’s disease on the basis of the patient’s history and physical examination, but the tests required to rule out
other diseases or disorders may require specialists in en-docrinology, neurology, cardiology, otolaryngology, and internal medicine. Diagnostic hearing tests may be ad-ministered by an audiologist. Surgical treatment of Ménière’s is usually performed by an otolaryngologist or otologist. A nutritionist or dietitian should be consulted to plan a low-salt diet for the patient.
Patients whose attacks are triggered by emotional stress may be helped by therapists who teach biofeedback, meditation, or other techniques of stress reduction.
Treatment
Medical treatment
