Malignant Otitis Externa

2 Otology

3. Tympanomastoidectomy with canal wall down (CWD): indicated for large cholesteatomas, cholesteatomas with significant preoperative

2.3 Otitis Externa

2.3.2 Malignant Otitis Externa

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Evaluation

History

The history should focus on elucidation of predisposing factors, such as diabetes, immunosuppression, leukemia, alcoholism, and swimming. If the patient is diabetic, information regarding recent glucose levels and hemoglobin A1c (HbA1c) is useful.

Physical Exam

Include a microscopic ear exam with thorough cleaning of the ear canal and placement of a myringotomy tube if necessary. This may require general anesthetic if pain is severe. A complete head and neck exam with atten- tion to cranial nerves is also required. Parotid palpation and TMJ mobility is noted. See Table 2.7 for a consideration of diagnostic tests.

Imaging

CT of the temporal bone is often the initial study. Fluid is often seen in the mastoid and middle ear. More importantly, soft tissue edema can be seen in the ear canal and periauricular tissues, as well as the parapharyngeal, infratemporal, and subtemporal spaces. Bone erosion may or may not be detectable depending on its extent. CT is not especially helpful in determining the endpoint of treatment.

MRI of the skull base is helpful in detecting the progression of disease.

Gadolinium-enhanced studies with fat suppression will demonstrate involvement of the dura and other skull-base soft tissues.

Technetium-99m (^99mTc) nuclear scanning highlights areas of osteoblastic activity seen in osteomyelitis. Increased uptake indicative of skull-base Table 2.7 A Consideration of Key Diagnostic Tests for

Malignant Otitis Externa Labs

CBC with differential (follow ANC level if neutropenic), blood glucose level (serially), HbA1c, ESR (serially)

Pathology

Histopathologic exam of granulation tissue to exclude neoplasm Microbiology

Bacterial and fungal culture and sensitivities of ear canal debris Imaging

Temporal bone CT to assess for extent of disease, bone erosion

MRI with gadolinium may be helpful to assess dura, soft tissue involvement.

Nuclear scanning: Technetium-99m scan to assess for skull base osteomyelitis;

gallium-67 citrate nuclear scanning preferred for follow-up and assessment of disease resolution

Abbreviations: HbA1c, hemoglobin A1c; ANC, absolute neutrophil count; CBC, complete blood count;

CT, computed tomography; ESR, erythrocyte sedimentation rate; MRI, magnetic resonance imaging.

osteomyelitis is seen between 4 and 24 hours after ^99mTc administration.

This modality may be positive prior to bony changes seen on CT, but cannot be used to determine the endpoint of treatment, as it may remain positive for months to years as a sign of bony repair. It is very helpful in confirming an early diagnosis.

Gallium-67 (⁶⁷Ga) citrate nuclear scanning highlights areas of inflam- mation by binding to leukocytes. It also reverses back to normal once the inflammatory response has resolved, so it is helpful in determining the treatment endpoint. It may be repeated several times throughout the treatment course to monitor response.

Labs

Routine laboratory testing will display an increased WBC count, an increased ESR, and elevated blood glucose. Serial ESR levels can be used to monitor treatment response.

Other Tests

The ear canal should be swabbed for culture and sensitivity. Granulation tissue needs to be sent for permanent pathology sectioning. An audiogram is good as a baseline measure.

Pathology

Most often Pseudomonas aeruginosa is the causative bacteria. This should be confirmed with a culture. Infection begins at the skin of the EAC and spreads via venous channels and fascial planes. Infection can also spread to the skull base via fissures of Santorini and tympanomastoid suture line.

Cranial nerves become involved in the soft tissue inflammatory response at the stylomastoid foramen and the jugular foramen.

Patients are immunocompromised, most commonly secondary to diabetes mellitus. Their cerumen is neutral pH, not acidic, and many have had their ear canals irrigated with nonsterile tap water 2 to 3 weeks prior to symptom onset. Patients with human immunodeficiency virus (HIV) or hematologic malignancies are prone to fungal OE, mainly secondary to Aspergillus.

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Treatment Options

Medical

Medical therapy is the mainstay once the ear canal is cleaned and all granulation débrided. A myringotomy tube may be required if middle ear fluid is present. Once cultures and sensitivities return, long-term culture-directed antibiotics can be used (Table 2.8). Traditional therapy has been an IV anti- pseudomonal antibiotic and an aminoglycoside. Nephrotoxicity in diabetics given aminoglycosides is a concern, so ceftazidime has been given as monotherapy. Drug resistance, however, is a concern with monotherapy.

Fluoroquinolones, primarily ciprofloxacin, can be given orally with excel- lent cure rates, but again, concerns of drug resistance have arisen. As long as resistance does not emerge, oral fluoroquinolones can be used, and average

treatment durations are 4 to 6 weeks. A peripherally inserted central catheter (PICC) line or central venous catheter is typically required. If resistance emerges, then long-term IV management is required. The endpoint of therapy is individualized with gallium scanning, and treatment courses have been documented to run several months.

Surgical

Surgical management is limited to initial canal débridement and myringotomy tube placement if needed.

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Complications

Progressive MOE becomes osteomyelitis of the skull base. With spreading infection, CNs VII, IX, X, and XI may become involved. Consequences include aspiration with difficulties in speech and swallowing. CNs III, V, and VI may also be involved. Meningitis, lateral sinus thrombosis, cerebral abscess, and death may all occur.

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Outcome and Follow-Up

With proper diagnosis and treatment, cure rates are over 80%. Patient follow-up is dictated by symptoms. Treatment is complete when the TM and ear canal return to a normal appearance, pain resolves, ESR returns to normal, and the gallium scan returns to normal.

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ICD-9 Code

380.14 Malignant otitis externa