Smelly, Macerated Feet
Diagnosis: Pitted keratolysis (PK)

Patient Presentation A 24-year-old medical student presented with multiple, whitish papules and pits on the sole of his right foot. These papules, which had been there for about 6 months, first appeared while he was training for a triathlon. He indicated that the lesions were more noticeable during periods of intense exercise. His left foot was also affected. Four weeks earlier, he’d noticed the appearance of similar lesions on that foot. At this point, both soles of his feet were afflicted with macerated, whitish plaques. He also reported a slight malodor and hyperhidrosis of the feet with a decrease in sensation over the larger plaques on both soles. He denied pain or pruritus. On examination, we observed multiple 3-mm to 5-mm papules and pits involving most of the plantar surface of the patient’s feet. In addition, we noted several distinguished, whitish, macerated plaques with erosions and irregular borders. These lesions were mainly located over the area underlying the metatarsophalangeal joints (see above photo). The patient self-treated the lesions with topical benzoyl peroxide 4% gel once a day for 1 week. This resulted in mild improvement, but as soon as he stopped using the topical treatment he experienced a flare-up of the lesions. n What’s your diagnosis? (Turn to page 87 for an answer and details about the condition, including treatment options.) About this Condition Pitted keratolysis, also known as keratolysis plantare sulcatum, is a skin disorder characterized by pits and collarettes of the skin as a result of skin infection with bacterial species. Responsible agents include Micrococcus sedentarius, a Gram-positive Staphylococcus-related bacterium, Dermatophilus congolensis, a Gram-positive facultative anaerobic Actinomyces species, as well as some Corynebacterium species. All these bacteria share common features, which enable them to produce proteinases that destroy the stratum corneum and open small tunnels and pits. The localized absence of the stratum corneum leads to a punched-out appearance of the skin. The most commonly affected areas of the body include the plantar skin, especially pressure-bearing areas such as the ventral aspect of the toes and the ball of the foot. Some patients have lesions on the interdigital surfaces, but our patient wasn’t affected in these areas. PK is typically triggered when the feet are occluded by shoes for a prolonged time and when patients experiences hyperhidrosis and increased skin surface pH. PK is usually asymptomatic, although cases with severe tenderness and limitation of function have been reported. In recent reports, the use of transmission electron microscopy and scanning electron microscopy showed bacteria in the stratum corneum with typical transversal septations. Tunnel-like spaces were built inside the horny layer, where the bacteria exhibited a hairy surface.1 Malodor is common, and is presumed to be the production of sulfur-compound byproducts such as thiols, sulfides and thioesters. Cutaneous biopsy is rarely performed on a typical case of PK, and empiric treatment is often initiated by dermatologists. Candidal infections, basal cell nevus syndrome, and keratolysis exfoliativa may be considered in the differential diagnosis. Treatment Our patient was treated with topical clindamycin phosphate (Cleocin T solution) for 10 days with complete healing (see above photo). When managing patients with PK, your aim should be to reduce moisture by instructing patients to wear properly fitting shoes with absorbent cotton socks. Patients should frequently change their socks and avoid occluding their feet for long periods of time. In addition, applying antiperspirants such as aluminum chloride 20% solution is helpful in reducing hyperhidrosis. Inert antiseptic foot powders may also be used. Antimicrobial therapy with topical erythromycin or clindamycin applied to the entire plantar surfaces of the feet is effective. Topical mupirocin (Bactroban), benzoyl peroxide wash or gel, clotrimazole (Lotrimin, Mycelex), miconazole (Lotrimin AF, Micatin), and Whitfield’s ointment are also effective. Successful treatment with topical antiseptics, such as glutaraldehyde and formaldehyde, has also been reported. Oral erythromycin is another option, especially for resistant cases. This usually clears both the lesions and odor in 3 to 4 weeks.