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Malignant Otitis Media (Malignant Otitis Externa / Necrotizing Otitis Externa)

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INTRODUCTION AND TERMINOLOGY

Note on Nomenclature: The term "malignant" does not imply a neoplastic process. It was coined by Chandler in 1968 to reflect the aggressive, often fatal course. The condition was first described by Meltzer and Kelemen in 1959. The term "Necrotizing Otitis Externa" or "Skull Base Osteomyelitis" better describes its pathophysiology.

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EPIDEMIOLOGY

• Predominantly affects elderly diabetic patients - glucose intolerance may be present in up to 90% of cases
• Also seen in other immunocompromised states: HIV/AIDS, myeloid malignancies, pharmacological immunosuppression, organ transplant recipients
• Rarely reported in immunocompetent individuals
• Mortality: 5-20% even in the antibiotic era; higher with intracranial extension

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ETIOLOGY AND PATHOGENESIS

Why Diabetics Are Affected

1. Microangiopathy of the ear canal vessels - impairs local blood supply
2. Increased pH of cerumen in diabetics - promotes bacterial growth
3. Impaired polymorphonuclear leukocyte function - reduces ability to fight infection
4. Diabetic microangiopathy causes vascular thrombosis → coagulative necrosis of surrounding tissue

Causative Organism

• Pseudomonas aeruginosa accounts for >90% of cases
• Other organisms (rare): Staphylococcus aureus, S. epidermidis, Proteus mirabilis, Klebsiella oxytoca, fungal species
• Fungal MOE (rare): most commonly Aspergillus fumigatus, associated with HIV-positive patients; 84% of fungal MOE cases occur in immunocompromised individuals
• Fluoroquinolone-resistant Pseudomonas is an increasing and concerning problem

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SPREAD AND PATHOLOGY

1. Starts in soft tissues of the EAC (skin and subcutaneous tissue of the cartilaginous canal)
2. Spreads to the tympanic bone via:
   • Fissures of Santorini (gaps in the cartilaginous floor of the EAC)
   • Tympanomastoid suture → stylomastoid foramen → jugular foramen
3. Hallmark: Does NOT spread through pneumatized tracts like typical temporal bone infections; the middle ear is rarely involved until late
4. Spreads via Haversian system of compact bone, forming multiple abscesses and bony sequestra
5. Extension pathways:
   • Petrotympanic fissure → temporomandibular joint (TMJ) and infratemporal fossa
   • Inferiorly → soft tissue spaces below skull base (periparotid, cervical)
   • Medially → carotid canal, jugular foramen
   • Intracranially → via venous channels and facial planes → dural sinuses

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CLINICAL FEATURES

Symptoms

• Severe, deep-seated otalgia - typically worse at night, out of proportion to examination findings
• Otorrhoea (ear discharge)
• Aural fullness
• Fever (may be absent even in active disease)

Signs

Key point: Multiple cranial neuropathies indicate a worse prognosis. The facial nerve is most commonly involved due to proximity of the stylomastoid foramen to the floor of the EAC.

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INVESTIGATIONS

1. Biopsy of Granulation Tissue

• Mandatory - both to rule out malignancy and for culture purposes
• Bacterial and fungal cultures must be sent simultaneously

2. Laboratory Tests

• ESR (Erythrocyte Sedimentation Rate): typically elevated; nonspecific but useful to follow treatment response and detect possible recurrence
• White blood cell count: may be normal even in active disease
• Blood glucose

3. Imaging

A. Nuclear Medicine (Most Important)

Memory tip: Tc-99 = Diagnosis; Ga-67 = Follow-up/treatment monitoring

B. CT Scan (High-Resolution Temporal Bone CT)

• Demonstrates bony erosion and soft tissue abnormalities around EAC
• Cannot distinguish infection from malignancy
• Significant bony erosion must occur before findings appear - early changes may be missed
• Not useful for following treatment response
• Early sign: subtle soft tissue thickening in EAC; later: cortical bone erosions

C. MRI

• Better than CT for detecting soft tissue changes and dural/intracranial involvement
• Imaging of choice when infection spreads beyond temporal bone (facial nerve or intracranially)
• MR Angiography can evaluate patency of dural sinuses

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DIAGNOSIS - COHEN AND FRIEDMAN CRITERIA

• Refractory otitis externa
• Severe nocturnal otalgia
• Purulent otorrhoea
• Granulation tissue in the EAC
• Positive Tc-99 bone scan
• Immunocompromised state (especially diabetes)

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TREATMENT

A. General / Supportive Measures

1. Aggressive blood glucose control in diabetic patients - essential and cannot be overemphasized
2. Correct other causes of immunodeficiency where possible (e.g., adjust immunosuppressive medications, treat HIV)
3. Pain management - analgesics (NSAIDs, opioids as needed)
4. Aural toilet / EAC debridement - regular cleaning of the ear canal (daily debridement)

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B. Antibiotic Therapy (Cornerstone of Treatment)

First-Line: Oral Fluoroquinolone

• Ciprofloxacin 750 mg orally twice daily is the antibiotic of choice for MOE
• Fluoroquinolones are the only oral antibiotics with reliable antipseudomonal activity
• Monotherapy with oral ciprofloxacin is effective in patients without intracranial complications or cranial neuropathies
• Dose recommended by Scott-Brown's: 1.5 g/day over 6-12 weeks

Duration of Treatment

• Minimum 6-8 weeks (Cummings, Scott-Brown's)
• Treatment should continue until clinical examination normalizes
• Can treat until Gallium-67 scan normalizes (most reliable endpoint, though may prolong treatment)

When to Escalate to IV/Parenteral Antibiotics

• Advanced cases (intracranial extension, cranial neuropathy)
• Failure of outpatient oral therapy (failure rate up to 33% in some series)
• When the patient cannot take oral medications
• In these cases: IV fluoroquinolone via PICC line, or parenteral antipseudomonal aminopenicillins
• Patients stable on IV can be discharged home with frequent outpatient debridement

Fluoroquinolone-Resistant Pseudomonas

• An increasing problem; may require:
  • 3rd or 4th generation cephalosporins (e.g., ceftazidime, cefepime) ± aminoglycoside
  • Culture-directed therapy is strongly preferred whenever cultures are available

Double Coverage

• Empiric double coverage directed against Pseudomonas is begun after cultures are obtained in advanced cases (Shambaugh)

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C. Antifungal Therapy (for Fungal MOE)

• Parenteral antifungal therapy for culture-positive fungal MOE
• Amphotericin B: traditionally used, but has significant side effects (nephrotoxicity, etc.)
• Voriconazole: now the preferred first-line therapy for invasive Aspergillosis; more favourable side-effect profile than Amphotericin B
• Other azoles (fluconazole, itraconazole) used depending on species and sensitivity

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D. Surgical Treatment

Important: Surgical intervention is NOT indicated for facial nerve paralysis in MOE - decompression of the facial nerve fails to address the extratemporal location of nerve involvement (Shambaugh). Heroic surgical measures are reserved for recalcitrant disease only.

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E. Hyperbaric Oxygen Therapy (HBO)

• The role of HBO in MOE is unproven (KJ Lee's)
• Theoretically benefits anaerobic wound healing and enhances neutrophil killing
• Used as an adjunct in refractory cases in some centers
• Not part of routine standard management

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MONITORING RESPONSE TO TREATMENT

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COMPLICATIONS

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PROGNOSIS

• Mortality: 5-20% in the antibiotic era
• Extension to skull base, cranial nerve involvement, and intracranial extension at presentation all correlate with higher mortality
• Good prognostic factors: early diagnosis, good diabetic control, culture-directed antibiotic therapy
• Relapse can occur; Gallium-67 monitoring helps detect recurrence

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CLINICAL IMAGES

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RECENT UPDATES IN TREATMENT (2021-2026)

1. Fluoroquinolone resistance in Pseudomonas is a growing challenge - culture-directed therapy is increasingly important
2. Fungal MOE is now well-recognized, especially in HIV patients (PMID 39534824 - Sideris et al., 2024 systematic review); voriconazole has largely replaced amphotericin B for Aspergillus
3. Diagnostic conundrum: NOE can be difficult to distinguish from other skull base pathologies - biopsy + imaging + nuclear medicine remain the diagnostic triad (PMID 38560038 - Ahmed et al., 2024)
4. Mortality data: A 2025 meta-analysis (PMID 40765727) confirms significant mortality, particularly with intracranial extension
5. Oral ciprofloxacin remains effective for uncomplicated MOE; intravenous options are needed for resistant or complicated disease

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SUMMARY TABLE

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