This man has pitted keratolysis (PK), characterized by multiple small pits on the soles of the feet. PK is often associated with hyperhidrosis and significant odor. The lesions usually have a punched-out appearance and are flesh-colored. The dark color of these lesions was due to the patient’s footwear.
PK is caused by bacterial overgrowth in the stratum corneum. Corynebacterium is the most common bacterial culprit, but Kytococcus, Actinomyces, and Dermatophilus have also been implicated. The bacterial infection is thought to be secondary to hyperhidrosis or as a result of hygiene, footwear, or other conditions that retain moisture and promote maceration of the soles of the feet. Therefore, treatment includes a 2-pronged approach: Resolve the bacterial infection and reduce excess moisture. Effective antibacterials include topical clindamycin, erythromycin, fusidic acid, and benzoyl peroxide. Oral antibiotics are not often required.
Hyperhidrosis can be treated with prescription strength 20% aluminum chloride antiperspirant applied to the feet in a tapering schedule, first daily and then 2 or 3 times weekly. Aluminum chloride is frequently not covered by insurance companies, but over-the-counter (OTC) 12% formulations (Certain DRI) usually suffice. Additionally, changing socks and using moisture-wicking shoes or socks are helpful measures to keep feet dry.
One study treated PK with topical erythromycin 3% gel twice daily, without the use of aluminum chloride antiperspirants, and found that the hyperhidrosis greatly improved. The authors theorized that the gram-positive bacterial infection upregulated eccrine sweat glands causing hyperhidrosis as a secondary, rather than the primary, cause of PK.
This patient was prescribed topical erythromycin gel twice daily for the soles of his feet. For his hyperhidrosis, he was advised to purchase OTC aluminum chloride antiperspirants to apply to his feet daily for the first week and to then decrease to 2 or 3 times per week. He was counseled to take an extra pair of socks for changing midway through his workday and to return for reevaluation if his skin did not improve.
Image courtesy of Sarah Friedberg, MD, and text courtesy of Daniel Stulberg, MD, FAAFP, and Sarah Friedberg, MD, Department of Family and Community Medicine, University of New Mexico School of Medicine, Albuquerque.