Answers

Short answers

1 The diagnosis is acute diffuse otitis externa with cellulitis of the pinna.

2 Pseudomonas aeruginosa and Staphylococcus aureus are the two most likely causative agents.

3 Patients with acute diffuse otitis externa with cellulitis should be treated with oral flucloxacillin, antimicrobial eardrops (such as hydrocortisone and gentamicin drops), and oral analgesics.

4 Referral to secondary care is advised when swelling or debris in the ear canal prevents the admission of eardrops.

Long answers
1 Diagnosis
The figure shows an erythematous pinna with yellowish discharge appearing to originate from the external auditory meatus. The fact that the patient initially presented with an itchy ear that became painful suggests strongly that the diagnosis is otitis externa. The hearing loss is owing to swelling of the ear canal, which decreases sound conduction. The cellulitis of the pinna is caused by the spread of infection from the ear canal.

2 Causative agents
The inflammation seen in otitis externa is often caused by microbial infection. In a prospective survey of 121 consecutive patients with otitis externa seen in secondary care, most cases were caused by bacteria (66%) and some were owing to fungal infection (15%).¹ Microbial culture revealed no growth in 20% of cases. The most common bacterial organisms identified were Pseudomonas aeruginosa and Staphylococcus aureus, whereas the most common fungal organisms were Candida and Aspergillus species.

In recurrent cases of otitis externa, there may be underlying dermatitis contributing to the pathogenesis.

3 Treatment
Most cases of simple diffuse otitis externa seen in primary care are successfully managed with topical therapy.² A systematic review concluded that topical antimicrobial therapy is highly effective for acute otitis externa, with clinical cure rates of 65-80% within 10 days.³ Interestingly, the choice of topical antimicrobial has minimal impact on cure rates: comparative clinical outcomes are seen with antiseptic, antibiotic, steroid only, and antimicrobial plus steroid preparations.³

When the infection has spread outside the ear canal (that is, in cases of cellulitis or perichondritis), guidelines published by the American Academy of Otolaryngology recommend the additional use of systemic antibiotics.⁴ Keeping the ear dry and avoiding cotton bud use will help to reduce exacerbation of the present condition and recurrence.

4 Referral
The majority of patients with otitis externa do not need to be referred for secondary care. Analysis of all cases of otitis externa occurring in 1997 in practices contributing to the General Practice Research Database revealed that of 30 412 patients, 807 patients (3%) were referred to secondary care.²

Referral to secondary care is advised when swelling or debris in the ear canal prevents the admission of eardrops. When the ear canal lumen is obliterated owing to oedema, insertion of a wick may be required to splint the canal and provide a route for topical therapy. Debris in the canal should also be cleared, possibly by microsuction, to allow access for topical therapy.

Referral should also be considered when there is extensive cellulitis or extreme pain.⁵ Further guidance on when to refer patients with acute diffuse otitis externa can be found at NHS Clinical Knowledge Summaries.⁵

Patient outcome
In this patient, the pinna was considerably less erythematous 48 hours after initiation of treatment and the external auditory canal was less inflamed. Aural toilet was performed and the patient was advised to complete the course of treatment. By the third follow-up visit the episode had resolved.

Cite this as: BMJ 2009;339:b3632