External Ear Conditions (Malignant Otitis Externa (MOE))

What is Malignant Otitis Externa?

The organism involved in MOE is invariably Pseudomonas aeruginosa. It is a condition that occurs primarily in diabetics who are generally elderly. The Pseudomonas subtype involved produces an exotoxin which in an immunocompromised environment allows the external ear infection to extend beyond the soft tissue confines of the external ear. Hence, the bony external ear becomes infected (osteomyelitis). If left unchecked, the infection spreads into the skull base and its soft tissues. At thia stage, the condition will progress rapidly towards the midline and involve the lower cranial nerves, brainstem, and ultimately result in death.

Clinical Features

The most notable feature is excessive pain in the presence of mild to moderate signs. The pain can interfere with sleep and the ability to function. The patients can look unwell or even toxic. Otorrhoea is usually scant and hearing is at mostly mildly affected. On examination, there is granulation tissue, usually at the bony-cartilaginous junction, scant discharge and an intact eardrum. The lower cranial nerves can be affected. The most common is the facial nerve. Hence, an external ear infection with an ipsilateral facial palsy implies malignant otitis externa.

Investigations

Investigation for MOE are aimed at confirming the diagnosis and determining the extent of disease. Culture and sensitivity and biopsy of granulations are taken. A CT scan of the temporal bone is performed to determined the extend of bony destructon. An MRI scan is crucial in revealing the extent of soft tissue involvement and helpful in differentiating between inflammaton and tumour, e.g. nasopharyngeal cancer. Serial MRIs are done to assess the efficacy of treatment. Occasionally, a bone scan (Gallium) is done. This will reveal hyperintensity of the infected area if osteomyelitis is present.

Management

All patients with suspectedof confirmed MOE are admitted. The aim is to start intensive pharmacological therapy, monitor progression (or resolution) and control predisposing conditions (e.g. diabetes). An anti-pseudomonal antibiotic (Ciprofloxacin, Ceftazidine) is started intravenously for a minimum of eight weeks. Whether combination therapy improves outcome is still a subject of debate. Pain relief and control of diabetes mellitus is also important. The external ear canal is cleared regularly using microsuction. Surgical intervention is limited to clearance of sequestra within the external ear canal and facial nerve decompression when indicated.
*Note: The importance of early diagnosis in patients with MOE cannot be over-emphasised. The early institution of treatment leads to reduced morbidity and mortality. When in doubt, refer patients

*ALL THE INFORMATION REGARDING THE EAR CONDITIONS ARE PROVIDED BY DR GERARD CHEE HSIEN. copyright reserved.