Malignant otitis externa

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Malignant otitis externa (MOE) is a severe variant of acute otitis externa (AOE) in which necrotizing inflammation of the external auditory canal (EAC) develops. MOE is usually caused by Pseudomonas aeruginosa and most frequently affects older adults and individuals with diabetes and/or immunosuppression. Clinical features of MOE include severe pain, an erythematous and edematous EAC, and otorrhea; granulation tissue is visible on otoscopy. Because of the rapid spread of infection, patients may have signs of complications (e.g., cranial nerve palsies secondary to osteomyelitis of the skull base) on initial presentation. Imaging and laboratory studies are recommended to confirm the diagnosis. Treatment is with IV antibiotics; surgery may be required for debridement or abscess drainage. The prognosis with treatment is good, with overall mortality < 10%.

• Pathogens ^[2][3][4]
  • Similar to acute otitis externa (see “Etiology of OE”)
  • P. aeruginosa is the most common cause, particularly in patients with diabetes. ^[4][5]
• Risk factors for MOE ^[3][4]
  • Older adults (> 60 years of age)
  • Diabetes mellitus
  • Immunosuppression

• Severe, persistent ear pain and/or jaw pain ^[3]
• Symptoms of extension of infection, e.g.:
  • Headache ^[3]
  • Facial nerve palsy in osteomyelitis of the skull base ^[2]
• Conductive hearing loss
• Red and swollen; EAC and periauricular soft tissue ^[6]
• Otorrhea
• Otoscopic findings: granulation tissue at the cartilage-bone junction of the EAC ^[2]

All patients require laboratory studies and imaging.

Laboratory studies ^[2][3]

• CBC: for WBC ^[3]
• BMP: for serum glucose and creatinine
• ESR and CRP ^[3]
• Culture of ear canal : Obtain a sample prior to initiating empiric antibiotics.

Imaging ^[3]

More than one imaging modality is often required.

• Modalities ^[7]
  • CT head with IV contrast: preferred initial study
  • MRI head: best modality for detecting soft tissue extension and intracranial abnormalities
  • Radionuclide scans: may be useful for early detection ^[7][8]
  • PET/CT scan: helpful for diagnosis and monitoring treatment response
• Findings
  • Bone erosion
  • Soft tissue involvement
  • Intracranial extension
  • Abscess

A negative CT scan does not exclude early MOE, as changes may not be evident until one-third of bone mineral is eroded. ^[9]

Surgical biopsy ^[3]

Consider if there is diagnostic uncertainty or insufficient response to treatment.

Treatment involves early empiric antibiotic therapy and the control of risk factors for MOE (e.g., diabetes or immunosuppression), in consultation with an otolaryngologist. ^[2][3]

Antibiotic therapy ^[3][4][9]

• Systemic antibiotic therapy: typically lasting for 6–8 weeks ; ^[3][4]
  • Initial empiric therapy: Use two antipseudomonal agents from different classes for ≥ 2 weeks, e.g., ciprofloxacin PLUS one of the following:
    • Ceftazidime ^[3][9]
    • Piperacillin/tazobactam ^[3][9]
    • Cefepime ^[3][9]
  • Once culture results are available, tailor antibiotics to sensitivities and continue for an additional 4–6 weeks.
• Local treatment ^[9]
  • Clean and remove debris from the EAC.
  • Consider topical antimicrobial therapy for AOE. ^[6]
    • Obtain a culture first.
    • Use an antipseudomonal agent plus a glucocorticoid. ^[10]

Surgery ^[2][3]

• May be required in select cases, e.g., abscess drainage or debridement of bony sequestra
• Send any surgical specimens for pathology and microbiological testing.

Patients unresponsive to antibiotic therapy may require a surgical biopsy to rule out fungal etiology or malignancy. ^[3]

Disposition ^[11]

• Urgent otolaryngology consult
• Patients typically require initial hospitalization followed by outpatient care for prolonged IV antibiotics.

Monitoring of treatment response ^[2][3]

• Repeat ESR every few weeks.
• Consider PET/CT scan. ^[7][8]

• Osteomyelitis of the skull base manifesting with: ^[6]
  • Facial nerve palsy and, less commonly, other cranial neuropathies (e.g., of IX, X, XI, and XII) ^[3]
  • Meningitis
  • Cerebral abscess
  • Septic cerebral venous thrombosis
• Relapse in up to 20% of patients ^[3]

We list the most important complications. The selection is not exhaustive.

• Overall mortality: < 10% ^[3]
• Rates may be higher in patients aged over 80 years or with significant comorbidities. ^[3]

MOE is a severe infection that can be lethal without prompt treatment. Death is most commonly caused by intracranial complications. ^[9]