Investigations
1st investigations to order
pneumatic otoscopy
Test
Normal in patients with acute otitis externa (AOE) alone, but abnormal in patients with otitis media alone or in combination with AOE.
Result
normal
tympanometry
Test
Normal in patients with acute otitis externa (AOE) alone, but abnormal in patients with otitis media alone or in combination with AOE. May cause discomfort in patients with AOE.
Result
normal
Investigations to consider
ear culture
Test
Ear cultures are recommended in patients who fail to respond to conventional therapy, and results will direct the choice of systemic antibiotics.[3]
Result
growth of the causative pathogen
microscopy of exudate/debris from ear canal
Test
White filamentous hyphae are seen on microscopic examination of exudate/debris from the ear canal in fungal otitis externa (otomycosis).The presence of black spores indicates Aspergillus niger as the causative organism in fungal otitis externa (otomycosis).[1][3]
Result
white filamentous hyphae and/or black spores in otomycosis
CT scan of the temporal bone with intravenous contrast
Test
CT scans are recommended in patients who have persistent severe ear pain and fullness despite adequate medical therapy with topical and oral antibiotics. This is to rule out necrotising otitis externa. Clinical features that would suggest a need for a CT scan include pain that is disproportionate to the clinical findings and patients with granulation tissue along the floor of the external auditory canal, especially in patients with diabetes or those who are immunocompromised.[1]
Result
bony erosion and invasion of petrous apex or skull base
MRI of the brain and internal auditory canals (with and without gadolinium)
Test
Ordered in addition to CT scan when necrotising otitis externa is suspected, especially in patients with diabetes or those who are immunocompromised.
Result
soft tissue outside the confines of the external auditory canal
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