A 45-year-old woman is referred to dermatology for a “fungal infection” that has failed to respond to the following treatments: topical clotrimazole cream, topical miconazole cream, a 30-day course of oral terbinafine (250 mg/d), and a 2-month course of oral griseofulvin (unknown dose).The lesions are completely asymptomatic but quite worrisome to the patient since they manifested 6 months ago.
She has consulted at least 6 different providers—none of whom was a dermatologist but all of whom were certain of the diagnosis and thus felt no need to refer the patient. However, the passage of time and trail of ineffective treatments finally prompts the (albeit reluctant) decision to send the patient to dermatology.
On questioning, she denies any serious health problems, such as diabetes or immunosuppression. She has had no contact with any animals or children.
The lesions in question total 6; all are uniformly purplish brown, round, and macular, and they range from 5 mm to more than 3 cm. Most are located on the bilateral popliteal areas. The lesions have sharp, well-defined margins. Several have faintly raised papular margins that give the centers a slightly concave appearance.
Palpation reveals the complete absence of any surface disturbance, such as scaling or erosion. Thus, no KOH prep can be performed to check for fungal elements. Instead, a shave biopsy is performed, the results of which show a sawtooth-patterned lymphocytic infiltrate obliterating the normally smooth undulating dermoepidermal junction.
What’s the diagnosis?