A diabetic patient with left ear pain and green foul-smelling discharge has an edematous ear canal and purulent discharge with an obscured tympanic membrane. The most likely diagnosis is which of the following?

• A. Auricular cellulitis
• B. Acute mastoiditis
• C. Chronic otitis externa
• D. Malignant otitis externa

Answer: (D)

Malignant otitis externa is an infection that starts in the external auditory canal but invades the surrounding bone, most often the skull base and temporal bone, especially in diabetics or other immunocompromised patients. The diabetes here sets up a higher risk for invasive infection. The presentation fits because the patient has severe ear pain, a foul, green purulent discharge, and edema of the canal with the tympanic membrane obscured by swelling. In malignant otitis externa, the infection is deep and destructive rather than just a superficial canal infection, so the drum may not be visible and symptoms can be disproportionally severe.

This contrasts with a simple auricular cellulitis, which would mainly involve the outer ear itself (pinna) rather than the canal and would not typically present with an obscured tympanic membrane or the same depth of infection. Acute mastoiditis usually follows an acute otitis media with postauricular tenderness and swelling behind the ear, not just canal edema and canal discharge. Chronic otitis externa is a longer-standing condition and would not typically present acutely in a diabetic patient with this depth of infection.

In practice, suspecting malignant otitis externa prompts imaging (usually CT or MRI of the temporal bone) to assess bone involvement and skull base spread, and initiation of intravenous anti-pseudomonal antibiotics with careful monitoring, often for an extended course.