What is the better term for malignant otitis externa? Besides pseudomonas, what are the organism causing it? Justify your investigation.

Maligation otitis externa is a misnomer as it is not a neoplastic process.

The nomenclature of this condition is confusing as the term skull base osyeomyelitis and necrotizing external otitis are often interposed.

It has been suggested that necrotizing external otitis should be used for aggressive soft tissue infection in the absence of bony involvement and that the skull base osteomyelitis be used for the condition once bone infection is confirmed.

Beside pseudomonas the following organism causes it:

1. Pseudomonas aeruginosa 95% case
2. Aspergillus: usually in non-diabetic individuals
3. Gram positive and Gram negative bacteria e.g Staphylococcus. Epidermidis (Barrow and Levenson et al)

WORKUP OR INVESTIGATION IN MOE:

Otoscopy:

Reveals granulation tissue at the bony cartilagenous junction. The ear drum is usually normal. The external auditory canal skin is soggy and oedematous.
Cranial nerve palsies are common when the disease affects the skull base. The facial nerve is the most common nerve affected. As the disease progresses the lower three cranial nerves are affected close to the jugular foramen.
Intracranial complications like meningitis and brain abscess are also known to occur.

Role of imaging:

• Conventional radiology is of no use.
• CT scan is useful in assessing bone destruction.
• MRI is useful in assessing soft tissue involvement.
• Radionucleotide scans with Technetium 99 helps in assessing bone involvement

Imaging alogrithm in these patients are:
1. TC99 scan to seek evidence of bone involvement
2. If this is positive CT scan and MRI scan is a must to rule out bone and soft tissue involvement
3. Serial Ga 67 scans to assess the efficacy of treatment modality.

Levenson’s criteria for diagnosis of malignant otitis externa:

• Refractory otitis externa
• Severe nocturnal otalgia
• Purulent otorrhoea
• Granulation tissue in the external canal
• Growth of Pseudomonas aeruginosa from external canal
• Presence of diabetes and and other immuno-compromised state

 

 

Staging & classification:

 

 

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