Australian X disease See Murray Valley encephalitis
C. Gillespie syndrome Congenital ataxia with partial aniridia, infantile spasms, choreoathetosis, and
perreflexia, posterior column sensory loss, and dementia are also reported. The syndrome is associated with at-rophic changes in the cerebellum, basal ganglia, and spinal cord.2236,5894This must be the same condition as that formerly called ADCA II: with pigmentary retinal de-generation/progressive macular degeneration.
ADCA Type III: “Pure” Cerebellar Ataxias with Late Onset (Adult-onset cerebellar ataxia, olivopontocerebellar atrophy, parenchymatous cerebellar cortical atrophy, cerebellopontine atrophy, late cortical cerebellar atrophy, Marie-Foix Alajoua-nine syndrome, Thomas atrophy) This group of ataxic disor-ders is of unknown etiology with onset usually after the age of 50 years.2438Corticospinal, extrapyramidal, and ocular fea-tures are not prominent and sensory loss is absent. The chief pathological change is cerebellar cortical atrophy with loss of the Purkinje cell layer.179,2605
SCA5 Located on 11q13 (11 cen). This form presents as a slowly developing cerebellar and pyramidal syndrome in the third decade, with global cerebellar atrophy.4589a SCA6 Located on 19p13. This dominantly inherited form
re-sembles SCA5 but is manifested in older adults and poste-rior column function is impaired. Life span is normal.
Downbeat nystagmus is an added feature but the brainstem is otherwise unaffected. The mutation is allelic with episodic ataxia type 21997,2079,5347and linked to familial hemiplegic migraine both clinically and through shared abnormalities of the CACNA1A P/Q type calcium channel ␣1subunit.
SCA8 Located on 13q21. This is a slowly progressive form with cerebellar, pyramidal, and cognitive signs.2897 SCA11 Life span is normal. This form is not yet mapped.
Others
SCA9 Located on a chromosomal site not yet determined.
SCA10 Located on 22q13. This pure cerebellar syndrome has seizures as an added feature, and is described from Mexico.4606 A similar phenotype has been mapped to 22q.13.3704
SCA13 Located on 19q. This recessive form manifests in childhood. Psychomotor failure is reported.
SCA14 Located on 19q
SCA 15 (Unknown locus) This pure ataxic syndrome is re-ported in a single Australian family.5371
SCA16 Autosomal dominant form on 8q 22.1–24.1. Head and hand tremors are reported.
SCA17 Not completely characterized.
Dentato-rubro-pallido-luysian atrophy (DRPLA) Lo-cated on 12 p
SCA types 1, 2, 3, 6 and 7, 12, and DRPLA stem from mu-tations consisting of expanded and unstable CAG trinucleotide repeats. SCA8 results from an expansion of a CTG trinu-cleotide repeat. The types of mutations responsible for SCA4 and 5 and for SCA9 through 11 are unknown.5403See also Ramsay Hunt syndrome; mitochondrial diseases.
ADCA Type IV
Cerebellar signs with myoclonus and deafness characterize ths group (see Chart C–10) which may not be a distinct entity.
See May-White syndrome below, and MERRF.
Chart C–10. The (Spino)Cerebellar Ataxias III. Congenital inherited ataxias
A. Congenital ataxia with mental retardation with or without spasticity (includes pontoneocerebellar and granule cell hypoplasia); which are autosomal reces-sive or dominant, or X-linked. The various syndromes identified include the following:
Angelman syndrome
Ataxia with photomyoclonus A dominantly inherited syndrome characterized by extreme sensitivity to light, and with myoclonus, cerebellar ataxia, ataxic gait, pes cavus, kyphosis, and dementia.1625 The condition may also manifest later in life. This con-dition and MERRF (Myoclonus Epilepsy with Ragged Red Fibers) are probably the same.
Cerebellar hemisphere hypoplasia (congenital granular cell hypoplasia) A syndrome of ataxia and mental retardation, each of variable severity.5957
Congenital ataxia with choroidal coloboma (Pfeiffer syndrome)
Congenital cerebellar atrophy A dominantly inherited syndrome in which ataxia complicates early mild motor delay.1994
Lhermitte-Duclos disease (granular cell hypertrophy) Neonatal cerebellar atrophy with retinal dystrophy A fatal syndrome of neonatal ataxia with retinal dys-trophy and limitation of joint movement compli-cated by diarrhea, vomiting, pericardial effusion, and hepatic fibrosis.
Olivopontocerebellar atrophy with hepatic cirrhosis and retinal dystrophy A congenital inherited ataxic syn-drome with cerebellar hemisphere hypoplasia, char-acterized by pericarditis, neonatal feeding problems, hypotonia, pigmentary retinopathy, abnormal en-larged liver, joint contractures, and mental and de-velopmental delay.337
Paine syndrome
Pontocerebellar hypoplasia
Progressive ataxia, retinal degeneration, peripheral neu-ropathy, myopathy, and mental subnormality A rare congenital syndrome in which the above manifesta-tions are accompanied by hypoparathyroidism, dwarfism, malabsorption and cholelithiasis.2181 NARP syndrome (Neuropathy, Ataxia and Retinitis Pigmentosa).
B. Joubert syndrome (congenital ataxia, recessively
Argininosuccinuria Arginase deficiency Hyperornithinemia Aminoacidurias
Hartnup disease
Pyruvate and lactic acid dysmetabolism PDH deficiency
B. Progressive ataxic syndromes Abetalipoproteinemia Adrenoleukodystrophy Celiac disease
Cerebrotendinous xanthomatosis GDH deficiency
Hexosaminidase deficiency (GM2gangliosidosis) Hypobetalipoproteinemia
Hypoxanthine-guanine phosphoribotransferase deficiency
Krabbe leukodystrophy Metachromatic leukodystrophy Mitochondrial encephalomyopathies Neuronal ceroid lipofuscinosis Sialidosis
Sphingomyelin storage disorders Vitamin E deficiency
Wilson disease
X-linked ataxia, ichthyosis, and tapetoretinal dys-trophy (arylsulfatase C deficiency); see metachro-matic leukodystrophy
C. Ataxic disorders associated with defective DNA repair Ataxia-telangiectasia
Xeroderma pigmentosum Cockayne syndrome
III. Early-onset ataxias of unknown cause (onset usually before 20 years)
Friedreich ataxia Among the spinocerebellar degenera-tions in this group, this is the form most commonly diagnosed, but such a statement (while true globally) is inappropriate in certain parts of the world, where variants may be far more fre-quent. Next most commonly reported is the syndrome of early-onset cerebellar ataxia with retained reflexes (next en-try). Most of these syndromes are recessively inherited and dif-fer from Friedreich ataxia in the absence (with certain excep-tions as below) of optic atrophy, diabetes, cardiac involvement, and severe skeletal deformity.
Early-onset cerebellar ataxia of unknown cause (Friedreich ataxia with retained reflexes) This syndrome resembles Friedreich ataxia but with retention of the muscle stretch reflexes and with a better prospect of continuing func-tion.3090
This group includes ataxic syndromes complicated by my-oclonus (see Ramsay Hunt syndrome) while occasional families have also been described in which the ataxia is as-sociated with deafness, tapetoretinal or pigmentary retinal degeneration, optic atrophy, macular degeneration, demen-tia, extrapyramidal disorders, peripheral neuropathy, etc., as follows:
Ataxia with isolated vitamin E deficiency Hypo- or hypergonadism
Ataxia with hypergonadotrophic hypogonadism (Skre syndrome) A recessively inherited syndrome of gait and limb ataxia, also characterized by cataract, pri-mary amenorrhea, streak ovaries, small testes,
oph-thalmoplegias, loss of pain sensation, and mental and developmental delay.3710
Ataxia with hypogonadotrophic hypergodadism (Holmes syndrome) A recessively inherited syndrome of gait and limb ataxia, with onset in youth or early adult life. The condition is also characterized by pigmen-tary retinopathy, small penis and testes, pes cavus, dementia, hypotonia, dysarthria, choreoathetosis, distal weakness and wasting, loss of pain and joint position senses, short stature, and mental and devel-opmental delay.2619
Myoclonus
Ramsay Hunt syndrome This represents more than one condition, including mitochondrial encephalo-myopathy, sialidosis, and Baltic myoclonus. See progressive myoclonus epilepsy.
Childhood ataxia with diffuse central nervous system demyelination A progressive neurological disorder, also classified as a leukodystrophy, characterized clin-ically by progressive ataxic diplegia with onset before the age of 5 and with MRI and pathological evidence of confluent white matter disease.4960See CACH.
Childhood deafness
Ataxia with sensory deafness and optic atrophy A dom-inantly inherited ataxic syndrome with onset in childhood, characterized by sensorineural deafness, optic atrophy, and neurogenic muscle atrophy.337 Congenital deafness
Ataxia with deaf-mutism and muscular wasting 1. (early onset) A congenital inherited ataxic syndrome char-acterized by sensorineural deafness, pyramidal signs, neurogenic muscle atrophy with fasciculations, and thick-fiber sensory neuropathy.17142. (late onset) An inherited ataxic syndrome characterized by sen-sorineural deafness, endocrinopathy, spasticity, ax-onal motor neuropathy, and thick-fiber sensory neu-ropathy.1714
Optic atrophy with or without mental retardation Behr syndrome
Richards-Rundle syndrome Cataract and mental retardation
Marinesco Sjögren syndrome A recessively inherited ataxic syndrome with onset in childhood, also charac-terized by cataract, proximal and distal myopathy, and mental and developmental delay.3623
Pigmentary retinopathy
Ataxia with retinal degeneration A dominantly inher-ited ataxic syndrome characterized variously by such additional features as macular degeneration, optic at-rophy, pigmentary retinopathy, nerve deafness, pe-ripheral neuropathy, mental retardation, external oph-thalmoplegia, pyramidal and extrapyramidal signs, myoclonus, myocardial sclerosis and skin lesions, and the presence of abnormal mitochondria.2440,2804 Kin-ships in which this syndrome is recessively inherited are also described.2440See also MERRF.
Other variant early-onset ataxias of unknown etiology in-clude the following:
Ataxia with albinism An inherited ataxic syndrome char-acterized by dysarthria, motor neuropathy, diffuse de-pigmentation of skin, and mental and developmental delay.337
CEREBELLAR ATAXIA 165
Ataxia with deaf-mutism and muscular wasting 1. (early onset) A congenital inherited ataxic syndrome charac-terized by sensorineural deafness, pyramidal signs, neu-rogenic muscle atrophy with fasciculations, and thick-fiber sensory neuropathy.2070 2. (late onset) An inherited ataxic syndrome with onset in adult life, char-acterized by sensorineural deafness, endocrinopathy, spasticity, axonal motor neuropathy, and thick-fiber sensory neuropathy.2070
Ataxia with ocular motor apraxia An inherited ataxic syn-drome with onset in infancy or childhood also charac-terized by chorea and athetosis.60This and ataxia-telangiectasia are possibly the same condition.
Ataxia with pallidonigroluysian atrophy and Lewy bodies3989 Ataxia with paroxysmal dystonia An inherited ataxic syn-drome with onset in infancy or childhood, also char-acterized by dysarthria, paroxysmal dystonia, and py-ramidal signs.2250
Ataxia with pupillary paralysis A static inherited ataxic syndrome with onset in early adult life in which these features accompany kyphoscoliosis, sixth nerve palsy, cataract, kyphoscoliosis and pes cavus.5425
Benign cerebellatr ataxia with extensive thermoanalgesia A dominantly inherited variant with associated demyelinat-ing neuropathy affectdemyelinat-ing especially the smaller fibers.4483 Early onset ataxia with cardiomyopathy and retained re-flexes A variant phenotype of Friedreich ataxia, also mapping to chromosome 9q.4304
Familial intermittent ataxia An X-linked recessive, parox-ysmal ataxic syndrome with onset in infancy or early childhood, also characterized by dysarthria, apraxias, neurodegenerative regression, and abnormal lactate and pyruvate metabolism.3444
Familial spinocerebellar degeneration with corneal dystro-phy An inherited ataxic syndrome with congenital or infantile onset, also characterized by cloudy corneas.337 Jeune syndrome
Myokymia and periodic ataxia An inherited ataxic syn-drome with onset in infancy and also characterized by paroxysmal dystonia and myokymia.4712
Progressive visual and hearing loss, progressive spastic para-plegia, cerebellar ataxia, and dementia A syndrome with these findings is inherited either as a dominant or as a recessive trait.
Spino-olivocerebellar degeneration with ophthalmoplegia A recessively inherited ataxic syndrome characterized by colobomas of the optic nerve, dementia, ophthalmople-gia, parapleophthalmople-gia, demyelination, and pancytopenia.1279 Wadia-Swami syndrome
X-linked cerebellar ataxias Rare syndromes characterized by various combinations of visual loss, mild spastic paraparesis, mental slowing, myoclonic seizures, ex-trapyramidal deficits, posterior column demyelination, peripheral motor neuropathy, and pes cavus with on-set in infancy.224,2440
Other rare variants occur (summarized by Baraitser335) in which cerebellar ataxia is combined with brachydactyly and nystagmus, erythrokeratodermia, glutathione deficiency, or skin hyperpigmentation.
IV. Late-onset ataxias
This group of dominantly inherited ataxic syndromes has an onset usually after 20 years of age, and is accompanied in most
cases by other neurological features such as dementia, optic atrophy, pigmentary retinopathy, or extrapyramidal signs.
Other variant forms include the following:
Cerebellar ataxia with myoclonus and deafness (May-White syndrome) A very slowly progressive, dominantly inher-ited syndrome characterized by the onset in late child-hood or adolescence of cerebellar ataxia and impaired vi-sion due to pigmentary retinopathy. Spasticity occurs in some cases, but mental deterioration is not found.3715 Idiopathic late-onset cerebellar ataxia A heterogeneous
group of familial or sporadic cerebellar syndromes with-out a known familial basis.2436
Adult-onset autosomal recessive ataxia with thalamic le-sions described once in a Finnish family.4589
Adult-onset cerebellar ataxia and sensory deafness (of Schimke) An inherited ataxic syndrome with onset in adult life, also manifesting sensorineural deafness and high arches of the feet.337
Familial periodic ataxia A syndrome characterized by the onset in childhood of attacks of ataxia, dysarthria, ver-tigo, and nystagmus lasting hours to days. Drowsiness, headache, fever, and vomiting may also occur. A response to acetazolamide has been reported. The signs usually re-mit completely between attacks.1490Similarities to basi-lar migraine are notable.
Ataxia and other neurological deficits with hyperuricemia An inherited ataxic syndrome with onset in youth or adult life, characterized by ophthalmoplegia, facial palsy, sen-sorineural deafness, dysarthria, cardiomyopathy, nephro-pathy, and hyperuricemia.337
Ataxia with cataracts, hemiballismus, and dementia An in-herited ataxic syndrome with onset in adult life, also char-acterized by cataract, tics, pyramidal and extrapyramidal signs, muscle cramp, and dementia.337
Ataxia with downbeat nystagmus A recessively inherited ataxic syndrome with onset in young adult life charac-terized also by dysarthria, dysphagia, vertical nystagmus, and pyramidal signs.337
Ataxia with fasciculations A dominantly inherited condition with onset in young adult life, described (once) in India.5184 Ataxia with ichthyosis and hepatosplenomegaly (of Harper) An inherited ataxic syndrome with onset in mature adult life, characterized by dysarthria, enlarged liver and spleen, de-mentia, ophthalmoplegia, hyperkeratosis, and ichthyosis.337 Benign hereditary cerebellar ataxia with extensive ther-moanalgesia A dominantly inherited variant in which a length-dependent axonal neuropathy results from the loss of primary sensory afferents subserving pain and temperature sensation.4483
Spinocerebellar degeneration with motor system involve-ment A rare variant with onset in adult life, character-ized by ataxia, amyotrophy, and ophthalmoplegia, re-sembling the spinocerebellar degenerative diseases.2486 Pyramidal signs and generalized neuropathic muscle at-rophy and weakness leading to respiratory difficulties have also been described in this cluster.
Ataxia with vitamin E deficiency4277 Ataxia-telangiectasia
Spinopontine degeneration
Ataxia with photomyoclonus and skeletal deformities An in-herited ataxic syndrome with onset in adult life and char-acterized by dysarthria kyphosis, high arches of feet, de-mentia, and myoclonus.337
166 CEREBELLAR ATAXIA
Autosomal recessive late-onset ataxia A rare, recessively in-herited syndrome with onset in adult life, characterized by ataxia, supranuclear ophthalmoplegias, facial impas-sivity, pseudobulbar and pyramidal signs, peripheral neu-ropathy, and pure cerebellar cortical atrophy.2443 Thala-mic lesions also may occur.4589
Familial cerebellar ataxia with cerebrovascular amyloid An inherited ataxic syndrome with onset in young adult life, characterized by dementia, pyramidal signs, and cere-brovascular disease.3482
Familial spastic ataxia A dominantly inherited ataxic syn-drome with onset at any age, characterized by spastic-ataxic dysarthria, dementia, vertical nystagmus, optic at-rophy, pyramidal signs, and variable sensory neuropathic signs.
Late-onset hereditary ataxia with global thermoanalgesia and absence of fungiform papillae on the tongue An ataxic syn-drome, probably dominantly inherited, with these fea-tures and sensorineural deafness, canal paresis, ageusia, and numerous signs of autonomic disease, thus resem-bling hereditary sensory and autonomic neuropathy types 2 or 3. The onset in the single Japanese report pub-lished was in mid-adult life.1986
IVa. Late-onset recessive ataxias
These are very rare; no diagnostic criteria are available.
Baraitser335summarized the reports of the adult-onset cere-bellar ataxias in group IV above (cerecere-bellar ataxia plus) and classified them as follows:
1. Syndromes with added ophthalmological signs and pyramidal or extrapyramidal signs
2. Syndromes with added retinitis pigmentosa 3. Syndromes with added peripheral neuropathy; in
which features of hereditary motor and sensory neu-ropathy are found in association with cerebellar ataxia. One such syndrome is Ziegler syndrome, in which ataxia, rigidity, fasciculations, parkinsonism, and signs of peripheral neuropathy are found.
4. Late-onset pure cerebellar ataxias without associated features. These comprise two groups of “pure” ataxic syndromes with onset in adult life:
A. Recessive inheritance Those ataxias inherited re-cessively are rarer than other recessive ataxias.
They may be variously associated with downbeat nystagmus, hypogonadism, deafness, pigmentary retinopathy, or optic atrophy.
B. Dominant inheritance These are rare syndromes in which affected family members also show other features apart from the ataxia and which thus are not completely pure.2436
Cerebellar ataxia is also a feature of the following syn-dromes, noted elsewhere:
Ataxia-telangiectasia Chediak-Higashi syndrome Flynn-Aird syndrome Hartnup disease
Ketotic hyperglycinemia Nonketotic hyperglycinemia Pyruvate decarboxylase Richards Rundle syndrome
deficiency
Intermittent branched-chain ketoaciduria
See also Biemond ataxia, Kuru, hypertrophia musculorum vera, periodic ataxias, idiopathic late-onset cerebellar atax-ias, Joseph disease, delayed-onset cerebellar syndrome.
V. Episodic ataxias (periodic ataxias, hereditary paroxysmal cerebellar ataxia)
These are channelopathies, of which two dominantly in-herited forms are decribed, one with brief attacks from child-hood, precipitated by exercise and startle and complicated by jouint contractures and myokymia, mapping to 12p and due to a mutation of the potassium channel gene KCNA1. The other is characterized by attacks lasting hours to days, precip-itated by stress, exercise, and fatigue, with a progressive cere-bellar syndrome and permanent gaze-evoked nystagmus; it maps to 19p. Both respond to acetazolamide.2407 See also pyruvate decarboxylase deficiency, pyruvate dehydrogenase deficiency, maple syrup urine disease, Hartnup disease, and defects of ammomia metabolism.
VI. Hereditary spastic parapareses/paraplegias
This final group again includes both pure and compli-cated forms. An historical review was provided by Konigs-mark and Weiner.3125See hereditary spastic paraparesis.
Adapted from Harding AE. Clinical features and classification of inher-ited ataxias. Advances in Neurology, Chapter 1. New York: Raven Press, 1993, and Baraitser M. The Genetics of Neurological Disorders. Oxford:
Oxford University Press, 1990. A further classification, relying upon ge-netic data, will surely be adopted in time.
cerebellar ataxia with celiac disease The concur-rence of these conditions; the patients do not have spe-cific or diagnostic neurological signs other than the ataxia.4394
cerebellar ataxia with crossed third nerve palsy (Claude syndrome) A lacunar syndrome presenting with dysarthria, cerebellar ataxia, and facial numb-ness.1853,1867
cerebellar ataxia with hypogonadotrophic hypogo-nadism See cerebellar ataxias.
cerebellar ataxia with myoclonus and deafness See cerebellar ataxias.
cerebellar ataxia with retained reflexes See cere-bellar ataxias.
cerebellar ataxia with retinal degeneration See cerebellar ataxias.
cerebellar catalepsy sign Oscillation of the trunk and legs of patients with cerebellar lesions when their legs, flexed at the hips and knees, are passively raised from the bed. The sign was described by Babin´ski in 1902, but has not found favor.285
cerebellar cataplexy (cerebellar catatonia) The abil-ity of certain patients with cerebellar disease to hold a static posture of the legs with statuesque immobility while they cannot walk or move the legs through space without gross ataxia. The phenomenon differentiates between sensory ataxias and those of cerebellar ori-gin.1350 This sign was first described by Babin´ski in 1902.
cerebellar catatonia See cerebellar cataplexy.
cerebellar cognitive affective syndrome Behavioral changes occurring in patients with lesions involving the posterior lobe of the cerebellum and the vermis, char-CEREBELLAR COGNITIVE AFFECTIVE SYNDROME 167
acterized by impairment of executive functions such as planning, set-shifting, verbal fluency, abstract reason-ing, and working memory; difficulties with spatial cog-nition including visual–spatial organization and mem-ory; personality change with blunting of affect or disinhibited and inappropriate behavior; and language deficits including agrammatism and dysprosodia. Le-sions of the anterior lobe of the cerebellum produce only minor changes in executive and visual–spatial functions.
The constellation of deficits is suggestive of disrup-tion of the cerebellar moduladisrup-tion of neural circuits that link prefrontal, posterior parietal, superior temporal, and limbic cortices with the cerebellum.4973
cerebellar cortical degeneration An autoimmune nonmetastatic paraneoplastic syndrome of the CNS manifesting evidence of widespread cerebellar atrophy with loss of Purkinje cells, occurring in patients with carcinoma of the bronchus or ovary or with lymphoma, and in which an immunologic response induced by the tumor causes a secondary immune reaction in specific brain areas because of shared antigens.711
cerebellar diaschisis A reduction in blood flow and oxygen utilization in the cerebellar hemisphere con-tralateral to a supratentorial infarct,369,370due to an in-terruption of afferent input along the corticoponto-cerebellar pathway.
cerebellar diplegia The term applied by Frederick Bat-ten in 1903 to what is now known as ataxic cerebral palsy.
cerebellar disorders Syndromes characterized by ataxia, nystagmus, alterations in muscle tone, and gait disorder resulting from disorders affecting the cere-bellum or its connections.
These are classified in this book as cerebellar atax-ias in which there is a known hereditary basis for the condition; as ataxic syndromes in which the ataxia is a major feature but no familial tendency is known; and randomly, where cerebellar signs occur as one feature of other syndromes.
cerebellar hemangioblastoma A malignant vascular tumor of the cerebellum, commonly occurring in pa-tients with Von Hippel–Lindau disease.
cerebellar hemisphere hypoplasia See cerebellar ataxias.
cerebellar imitation synkineses Similar movements occurring in the hand or foot 200 msec or so after the contralateral one is moved. This may occur in patients with cerebellar degenerative diseases.2891
cerebellar migraine A distinct form of late-onset au-tosomal dominant cerebellar ataxia in which the ataxia occurs during recovery from attacks of hemiplegic mi-graine, the patients ultimately suffering from persistent ataxia, with cerebellar atrophy shown radiologically.4665 See also familial hemiplegic migraine.
cerebellar mutism (mutism and subsequent dys-arthria) Loss of speech a day or two after an acute cere-bellar event such as removal of a chronic mid-cerebel-lar tumor, or with stroke or encephalitis. Speech returns usually within 6 months, but is marred by severe dysarthria. Consciousness is retained and there are no accompanying deficits on examination of the lower cra-nial nerves, but in children, neurobehavioral disorders and pyramidal signs may be manifest. The mechanism is not determined but the condition is associated with hydrocephalus at presentation, localization of the tu-mor adjacent to the IV ventricle, and postsurgical edema of the pontine tegmentum.1305,5724
cerebellar outflow tremor See rubral or midbrain tremor.
cerebellar posture A term introduced by Batten in 1903 for that position of the head in which “the occiput is turned to one side and the chin to the other and at the same time flexed to the side to which the occiput was directed.” The same posture occurs after labyrinthine extirpation and “is the result of interfer-ence with a tonic reflex in which the extensor muscles of the neck, under the influence of impulses from the labyrinths, are maintained in a state of tonus adequate to resist the effect of gravity on the head.”706
cerebellar seizures See diencephalic autonomic seizures.
cerebellar signs Postural hypotonia, pendular re-flexes, asthenia and fatigability, ataxia, decomposition of movement, asynergy, nystagmus, dysmetria, tremor, loss of associated movements, drooping of the shoulder, and abnormalities in the rate, regularity, and force of voluntary movements occurring as a result of dis-ease of the cerebellum or of its connections.2625See cere-bellar tremors. In patients with cerecere-bellar tumors, symp-toms and signs have been defined as vertigo, deafness, tinnitus, weakness in homolateral conjugate gaze, sixth nerve palsies, skew deviation, horizontal jerk nystagmus, involvment of the fifth and seventh cranial nerves, ho-molateral limb weakness with asthenia, paresis of homo-lateral trunk muscles, hypotonia of the homohomo-lateral limbs, ataxia with reeling gait, intention tremor, postural deficits, and variable muscle stretch reflex activity.5357 cerebellar tonic seizures See diencephalic auto-nomic seizures.
cerebellar tremors Various forms of involuntary al-ternating movement due to disease of the cerebellum or of its connections. Such tremors are proximal, oc-cur with movement, displace the limb at right angles to the intended direction of movement, and increase in amplitude when they approach the target. The fre-quency is usually 5 Hz.
The various forms of cerebellar tremor have been classified by Sabra and Hallet4864(see Chart C–11). See also titubation.
168 CEREBELLAR CORTICAL DEGENERATION