malignant otitis externa

**Definition:** Also called necrotizing otitis externa. It is not a neoplasm; "malignant" refers to its aggressive, potentially fatal course. It is osteomyelitis of the temporal bone/skull base arising from external ear canal infection.

**Etiology / risk factors:** - Pseudomonas aeruginosa causes ~90% of cases. Fungi (Aspergillus) and MRSA are less common, and fungal cause is more likely in AIDS or in patients who fail antibacterial therapy. - Elderly patients with diabetes mellitus are the classic population (microangiopathy, impaired neutrophil function, and possibly altered cerumen pH). - Other risk factors: HIV/AIDS, chemotherapy, other immunosuppression, and aggressive ear irrigation or instrumentation.

**Pathophysiology:** Infection breaks through the Fissures of Santorini (cartilaginous canal) and the bony-cartilaginous junction. It then spreads to the soft tissue, temporomandibular joint, mastoid, and skull base (osteomyelitis). It may involve the jugular foramen, carotid canal, and cranial nerves, and may cause sigmoid/venous sinus thrombosis, meningitis, or intracranial abscess.

**Clinical features:** - Severe, deep otalgia, often worse at night, out of proportion to exam findings - Persistent purulent otorrhea that is unresponsive to topical therapy - Granulation tissue on the floor of the external auditory canal at the bony-cartilaginous junction (pathognomonic finding) - Trismus or TMJ pain, headache - Cranial nerve palsies: CN VII is the most common (facial palsy), followed by CN IX, X, and XI (jugular foramen) and, less commonly, CN VI and XII. Cranial neuropathy indicates advanced disease. - Fever is often absent. Leukocytosis is often minimal.

**Diagnosis:** - Clinical suspicion is critical: a diabetic or immunocompromised patient with otitis externa that does not respond to topical therapy. - ESR and CRP are elevated (useful for monitoring response to treatment). - Culture of the drainage or granulation tissue. Biopsy is needed to exclude malignancy (squamous cell carcinoma) and to identify fungi. - CT shows bony erosion of the skull base. MRI shows soft-tissue and marrow involvement. Technetium-99m bone scan is sensitive but not specific. Gallium-67 scan is used for monitoring response because it normalizes as the infection resolves.

**Management:** - Prolonged (usually 6–8+ weeks) systemic antipseudomonal therapy: oral/IV ciprofloxacin (or another fluoroquinolone), or an IV antipseudomonal beta-lactam (e.g., ceftazidime, cefepime, piperacillin-tazobactam) when the isolate is resistant to fluoroquinolones or in more severe cases. - Strict glycemic control and correction of immunosuppression where possible - Aural toilet and limited surgical debridement of necrotic tissue or abscess (surgery is not routine) - Antifungal therapy (e.g., voriconazole) if fungal - Hyperbaric oxygen is of unproven benefit. - Topical therapy alone is inadequate.

**Complications / prognosis:** Cranial neuropathy, meningitis, sigmoid sinus thrombosis, brain abscess, and death. Historically mortality was 50% or higher, but it has fallen with fluoroquinolones. Relapse is common.

**High-yield board pearls:** - Elderly diabetic with severe ear pain, otorrhea, and granulation tissue in the ear canal → think malignant otitis externa → Pseudomonas. - Facial nerve palsy is the most common cranial neuropathy. - Simple otitis externa ("swimmer's ear") is treated with topical agents. Malignant otitis externa requires systemic antibiotics. - The gallium scan is used to follow response to treatment, and CT is used to identify bony erosion. - Differential diagnosis includes SCC of the ear canal, so biopsy is needed in refractory cases.