USMLE Step 3: What’s causing patient’s ear pain, irritation?

If you are preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer.Also check out all posts in this series.  

This month’s stumper

A generally healthy 32-year-old man comes to see you because of pain in the right ear for the last few days. A discharge is coming from his ear. It is visible on his shirt as it drips out. He explains that his ear is very itchy, making him very uncomfortable.

The patient is upset because he cleans his ears vigorously with cotton swabs and frequently submerges his whole head in the bath, and he just does "not understand how someone as clean as me gets an infection like this." On physical examination he is afebrile. The external auditory canal is edematous and a discharge is visible. The tragus is painful with traction of the ear.

What is the next best step in the management of this patient?

A. Culture of the external auditory canal.

B. Intravenous piperacillin/tazobactam.

C. MRI of the bone surrounding the ear canal.

D. Topical polymyxin/neomycin/hydrocortisone.

E. X-ray of the skull bones.









The correct answer is D.

Kaplan Medical explains why

The patient has otitis externa, a cellulitis of the external auditory canal. Otitis externa can be managed with any number of topical antibiotics and steroids. Because the antibiotics are applied topically into the external auditory canal, an agent that would otherwise be too toxic can be used. In addition to polymyxin and neomycin, the following antibiotics are acceptable for use:

  • Ciprofloxacin, ofloxacin, norfloxacin.
  • Gentamicin, tobramycin.
  • Sulfisoxazole.

Hydrocortisone is used as a topical steroid because it is essential for decreasing inflammation and cleaning out the ear canal of debris.

Why the other answers are wrong

This person does not have "malignant (or necrotizing) otitis externa," a difficult term because it is actually an osteomyelitis of the cranial bones near the ear canal. As such, it is an infection and not a malignancy. "Malignant" is used in this disease name because of the severe infection and high mortality it causes.

It is an osteomyelitis—not an otitis. It is not "external" at all since it results from Pseudomonas rapidly eating through the cranial bones. The patient here does not have malignant otitis externa because he does not have a fever, diabetes, signs of severe systemic infection, or uncontrolled diabetes.

Choice A: Otitis externa is a mild, superficial infection that should resolve in the two or three days it would take for a culture to grow. There is no point in doing a culture.

Choices B, C and E: Intravenous piperacillin/tazobactam, MRI of the skull, and x-ray also are unnecessary.

Tips to remember

  • Otitis externa is treated empirically with topical antibiotics such as polymyxin, neomycin, colistin, and aminoglycosides combined with topical steroids to decrease inflammation.
  • This is more important than culture for specific microbiologic diagnosis.

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For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series..