Otitis externa usually results from bacteria (such as Pseudomonas aeruginosa, Staphylococcus aureus, group A streptococci), fungi (Aspergillus), yeast (Candida), or dermatologic conditions (seborrhea or psoriasis). Trauma to the middle ear, such as cleaning too vigorously with cotton-tipped swabs, can also cause otitis externa.

Without effective treatment, otitis externa can lead to otitis media and hearing loss. In patients with severe otitis externa, cellulitis, abscesses, discoloration, disfigurement of the pinna, lymphadenopathy, osteitis, septicemia, and stenosis may develop. Malignant otitis externa, most common in patients with type 1 diabetes mellitus and among the elderly, may develop as a result of a fulminant Pseudomonas infection.

Acute otitis externa characteristically produces moderate to severe pain that’s exacerbated by manipulating the auricle or tragus, clenching the teeth, opening the mouth, or chewing. Its other clinical effects may include fever, foul-smelling discharge, crusting in the external ear, regional cellulitis, partial hearing loss, and itching. It’s usually difficult to view the tympanic membrane because of pain in the external canal. Hearing acuity is normal unless complete occlusion has occurred.

Fungal otitis externa may be asymptomatic, although Aspergillus niger produces a black or gray, blotting, paperlike growth in the ear canal. In chronic otitis externa, pruritus replaces pain, and scratching may lead to scaling and skin thickening. Aural discharge may also be seen.

Otoscopy reveals a swollen external ear canal (sometimes to the point of complete closure), periauricular lymphadenopathy (tender nodes anterior to the tragus, posterior to the ear, or in the upper neck) and, occasionally, regional cellulitis. In fungal otitis externa, removal of the growth reveals thick, red epithelium. Pain on palpation of the tragus or auricle distinguishes acute otitis externa from acute otitis media. In chronic otitis externa, physical examination reveals thick, red epithelium in the ear canal. Severe chronic otitis externa may reflect underlying diabetes mellitus, hypothyroidism, or nephritis.