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ENT clinic - malignant otitis externa

ENT GPSI Dr Raj Singh looks at a common disease that is often misdiagnosed

 

Case

This 69-year-old woman presents with otalgia and left-sided hearing loss that had started three weeks previously.

She has no fever. Physical examination shows a slight swelling of the left auricle and of the temporomandibular region, and the left external auditory meatus shows an abundant purulent secretion. The patient was diagnosed with type 2 diabetes 10 years ago and was initially well controlled, but her HbA1c is currently 75mmol/mol – 9.5% – and she is taking metformin, gliclazide and pioglitazone.

She was treated by her GP with topical antibiotics, but 10 days later her symptoms have dramatically worsened, her lab tests show significant proteinuria and a raised ESR and there is some evidence of facial nerve palsy. The severe ear pain and headache prompt an admission where she is investigated for suspected malignant otitis externa. A CT scan of the left temporal bone shows opacification of the left middle ear and mastoid cavity, and a 5cm soft-tissue mass along the skull base consistent with bony destruction.

She is treated with IV antibiotics – vancomycin and meropenem – for two months, followed by oral ciprofloxacin. Insulin is used to quickly gain glycaemic control. Her condition improves and her inflammatory markers normalise. A repeat scan shows an improvement in the soft tissue along the skull base.

The problem

  • Malignant otitis externa is a rare but life-threatening extension of otitis externa into the mastoid and temporal bones, and can be fatal.
  • It is usually caused by Pseudomonas aeruginosa or Staphylococcus aureus and typically affects older patients with diabetes.
  • It is even rarer in younger patients where it is invariably associated with malnutrition or HIV infection.
  • The name is a poor one as it is not actually a malignant disease process, but an aggressive infection – an alternative term is necrotising external otitis.

Features

  • A hallmark feature is unrelenting pain that interferes with sleep and persists even after swelling of the external ear canal may have resolved with topical antibiotic treatment.
  • Typically presents with intermittent unilateral otorrhoea, progressive hearing loss and purulent otorrhoea.
  • There may be dysphagia, hoarseness and facial nerve dysfunction.
  • In later stages there can be soft-tissue swelling around the ear, even in the absence of significant canal swelling.

Diagnosis

  • ESR is invariably elevated, but leucocytes are usually normal or mildly elevated.
  • Granulation tissue in the floor of the osseocartilaginous junction is virtually pathognomonic of the disease and there may even be exposed bone on otoscopy.
  • Another key feature that distinguishes it from otitis externa is the pain, which often seems out of proportion to the physical findings.
  • Facial nerve palsy is a red-flag sign.

Management

  • If malignant otitis externa is suspected, urgent referral to ENT should be made.
  • CT or MRI scanning will determine the extent of the infection.
  • Bone scanning – with Technetium 99 – is often used to detect osteomyelitis.
  • Systemic antibiotic treatment is required for established disease – possibly for months if there is evidence of skull base osteomyelitis. Fluoroquinolones have dramatically improved the prognosis of this disease, though ciprofloxacin-resistant P. aeruginosa has been increasingly isolated in patients with malignant otitis externa.

 

Dr Raj Singh is an ENT GPSI in Manchester

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