An 18-year-old man is referred to dermatology for evaluation of bilateral “athlete’s foot” present for months despite the application of tolnaftate and clotrimazole creams. These both relieved itching, but the problem quickly returned, especially when the weather turned warm.

Besides objecting to his foot odor, the patient’s family also worries that his condition is contagious—even though the man’s father already has occasional athlete’s foot. Aside from mild seasonal allergies, the patient is reportedly in excellent health. He has never had any significant skin diseases and is not taking any medications regularly.

Inspection of the problem reveals marked maceration bilaterally between the fourth and fifth toes, under which is faint erythema. A KOH prep of the readily obtained material is examined microscopically under the usual 10x magnification, and numerous hyphal (fungal) elements are positively identified, in effect confirming the diagnosis of tinea pedis.

ANSWER
The one thing least likely to help is changing to white socks (choice “a”), since there is no reason to believe sock color has any effect, one way or the other, on the problem. There are numerous myths in society regarding athlete’s foot; these will be addressed in the discussion section.

When treatment appears to fail, it is usually a good idea to consider other diagnostic possibilities (choice “b”). In this case, these might have included bacterial or yeast infection, among others.

In stubborn or severe cases of tinea pedis, a 10- to 14-day course of terbinafine (choice “c”) is an acceptable treatment option, with only a modest risk of untoward effects. Continued topical application of terbinafine or other prescription-strength antifungal cream will probably be necessary to prevent flares.

Patient and family education (choice “d”) is arguably the single most important step to take in such cases, for reasons that will be delineated in the discussion.

DISCUSSION
This case illustrates several aspects of this diagnosis, which is estimated to affect up to 70% of the general population at one time or another in their lives. Our patient’s age, the presentation of the condition—very specifically affecting the webspace between the fourth and fifth toes (between the third and fourth toes far less commonly)—and the presence of chronic itching and maceration are all quite typical of this most common form of tinea pedis.

But just as typical is the persistent nature of the problem: Despite treatment, it often recurs, much to the patient’s distress. The two creams the patient had tried were among the least effective choices (massive advertising campaigns notwithstanding). Eventually, the patient’s immune system will likely fend off this infection; better bathing habits, less occlusive footwear, and less sweating can help. “Catching” this form of tinea pedis is related far more to these favorable conditions and to individual susceptibility than it is to the inevitable exposure to this ubiquitous dermatophyte.

Surprisingly, the first reports of this diagnosis in the United States were not made until the 1920s. The suspicion was that the organism, Trichophyton rubrum, had spread from very limited endemic areas to the rest of the world as a result of the massive movement of soldiers and civilian populations during and after WWI. The general increase in more occlusive forms of footwear was also thought to be a contributing factor.

Many myths sprang up over time regarding this condition. The “white sock” myth was so prevalent that it was probably responsible for two generations’ predominant choice of sock color. The use of white socks was also mistakenly thought to ward off foot odor, which in turn was thought to be caused by fungi.

Regarding the supposed contagious nature of the interdigital form of tinea pedis: Many a married couple has coexisted for decades without the husband “giving” it to the spouse, who is far less likely to represent a favorable host.

Three other forms of tinea pedis eventually evolved, including the hyperkeratotic type (also known as “moccasin variety” tinea pedis), which presents with a scaly, asymptomatic chronic rash around the rim of the feet; the inflammatory type, which presents with the acute appearance of vesicles and pustules on the soles of the feet, is highly pruritic, and almost always has a zoophilic source (cats being the most common); and the far less common ulcerative type, which presents with extensive vesicles, blisters, and erosions, is most often seen on the feet of patients with severe diabetes living in hot, humid conditions, and is usually from zoophilic sources as well.

When reasonable treatment fails, or KOH is negative, or the diagnosis is in doubt for any reason, consideration must be given to other potential explanations. For example, a similar condition can be caused by gram-negative organisms such as Proteus or Pseudomonas. A gram-positive organism called Corynebacterium minitissimum can eventuate in a chronic interdigital rash. Staph and strep can gain entry to the skin through preexisting, tinea pedis–caused breaks in the skin and eventuate in impressive cases of cellulitis, sometimes affecting the entire leg. Contact dermatitis, eczema, and psoriasis also belong in the differential.

Our patient was successfully treated with OTC terbinafine cream.