Foot Rash + Gnarly Toenails = Man in Need of a Diagnosis

ANSWER
The correct answer is to perform a KOH examination (choice “b”), which takes just five minutes and offers the chance to establish the fungal origin of the rash. Although the patient’s skin is quite dry, the use of a moisturizer (choice “a”) is unlikely to address the overall problem. A punch biopsy (choice “c”) would be a logical choice if the KOH failed to solve the mystery. The use of combination creams (choice “d”) that contain a steroid (triamcinolone) and an antifungal (nystatin) is essentially an admission of the lack of a definitive diagnosis. For reasons discussed below, this strategy has almost no chance of helping.

DISCUSSION
In this case, the KOH prep showed numerous hyphal elements, confirming suspicions of a fungal origin. One potential source of these organisms was the patient’s feet, where fungal infection had been present for years (“more than 30,” questioning revealed).

A common scenario is one in which the patient applies a steroid cream to a bit of dry skin just above the feet, which allows the fungi to gain a “foothold” from which to spread upward onto the leg; this progress is assisted through scratching and additional steroid application. If no firm diagnosis is ever established, definitive treatment cannot be undertaken and the problem never resolves.

In my opinion, there is never a reason to prescribe a product containing nystatin. In 1950, when it was discovered by researchers working in New York State laboratories (after which it was named), its efficacy against Candida species represented a notable advance, given the limited drug choices available for that purpose. But it has little, if any, activity against the dermatophytes causing our patient’s problems. And the steroid (triamcinolone) in this combination product, far from adding any therapeutic benefit, effectively diminishes any natural immune response.

The other reason to refrain from prescribing nystatin is that, since its discovery, at least three generations of products that treat both fungi and yeast (the azoles, such as clotrimazole, econazole, and fluconazole) have become available and have been found to be very effective.

The more important issue in this case, however, is finally having an accurate diagnosis: tinea corporis, probably caused by the most common dermatophyte, Trichophyton rubrum. The patient’s body is obviously a very happy home for this ubiquitous organism, to the extent that our chances of eliminating it are quite small. But we can at least make the patient more comfortable.

Treatment entailed ketoconazole foam (applied bid to his legs) and a two-month course of oral terbinafine (250 mg/d), which cleared up most of the skin problem. For his overgrown toenails, the patient was advised to establish care with a podiatrist for regular trimming.

In terms of a differential, this patient might have had psoriasis or eczema—and may still have one or both, since there’s no law against having more than one condition in the same location. In time, we may have to reconsider our solitary diagnosis.