Based on the pattern of the rash and the patient’s history, the family physician (FP) considered tinea corporis and cruris, but the history of failing treatment seemed unusual. The FP also considered a diagnosis of pityriasis rubra pilaris because he observed a “skip” area on the left thigh.
The FP performed a potassium hydroxide (KOH) preparation using a fungal stain and found branching septate hyphae. (See video on how to perform a KOH preparation here.) He also wondered if the failed treatment was secondary to inadequate dosing or duration of the oral medicines previously used, given that the patient was 6 feet, 5 inches tall and weighed more than 250 pounds. The patient didn’t have liver disease and rarely drank alcohol. Baseline liver function tests (LFTs) were within normal limits.
The FP told the patient to use oral terbinafine for one month rather than the recommended 2 weeks. One month later, there was less erythema and scaling, but the rash had not completely resolved. At that time, the FP and patient decided together to do a punch biopsy to make sure the diagnosis was correct. The punch biopsy supported the diagnosis of tinea with a positive periodic acid–Schiff stain for fungal elements; no other pathology was noted.
Since the LFTs were still normal, the FP and patient discussed a second month of treatment. The FP also performed a fungal culture and requested that the lab test the fungus for identification and sensitivities. Two weeks later, the results showed Trichophyton rubrum that was sensitive to all oral antifungal medications tested, including terbinafine.
At this point, the FP became concerned about the patient’s immune system, so he ordered a complete blood count (CBC) and human immunodeficiency virus (HIV) test. The CBC came back normal and the HIV test was negative. At the end of the second month, the fungal infection was still present clinically and the KOH preparation was still positive.
The FP offered oral itraconazole 100 mg/d and the patient was happy to try another therapy. The LFTs remained normal and after one month of itraconazole, the tinea was still present. At this point, the patient decided that he could live with the condition and would use a topical antifungal when the rash was itchy.
This case demonstrates a situation in which the patient’s immune system is “blind” to the foreign fungus. This has been known to happen with human papillomavirus, when patients have warts that do not resolve even with the most aggressive therapies.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Usatine R, Smith M. Tinea cruris. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013:795-798.
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