An otherwise healthy 10-year-old Caucasian male presented with a 2-year history of superficial circular erosions over the plantar feet associated with hyperhidrosis and malodour. There was no itch or pain. Family history was unremarkable. This had been treated as plantar warts and tinea pedis, with no improvement. Physical exam showed multiple discrete skin-coloured 1 to 5 mm crateriform erosions distributed on the heels and metatarsal pads (Figure 1). A diagnosis of pitted keratolysis was made.
Figure 1.
Multiple discrete skin-coloured 1 to 5 mm crateriform erosions over the base of the right plantar foot metatarsals.
Pitted keratolysis is a superficial bacterial infection affecting the feet caused by Gram-positive bacteria which digest the keratin and produce sulfur compounds, creating the characteristic pitting appearance and unpleasant odour (1,2). Risk factors include physical activity, hyperhidrosis, occlusive shoes, poor foot hygiene, obesity, and/or immunodeficiency (1,2). A warm, moist environment softens the stratum corneum leaving it ripe for the growth of Gram-positive bacteria such as Corynebacterium spp., Kytococcus sedentarius, Dermatophilus congolensis, and Streptomyces spp. (1–3).
Patients with pitted keratolysis typically have multiple discrete to coalescing circular erosions or pits measuring 1 to 7 mm on the weight-bearing parts of the feet. Lesions do not fluoresce on Wood’s lamp examination and dermoscopy may show black pits in a parallel pattern on the ridges of the stratum corneum (1,3).
The differential diagnosis of pitted keratolysis includes tinea pedis, verrucae (Figure 2), punctate palmoplantar keratoderma type 1, juvenile plantar dermatosis, and basal cell naevus syndrome (1).
Figure 2.
Multiple verrucous papules over the right plantar foot indicative of verruca vulgaris.
Treatments target hygiene, moisture management, and the bacterial infection. Hygiene and moisture management strategies include wearing clean breathable socks and footwear, as well as washing and drying feet daily (3). Treatments can also target any associated hyperhidrosis. The use of topical antibacterials such as benzoyl peroxide, fusidic acid, clindamycin, gentamycin, erythromycin, and muciprocin results in clinical cure within 3 weeks (1–3). There is no evidence oral antibiotics are effective at treating pitted keratolysis as they are unlikely to reach therapeutic levels in the plantar stratum corneum (2). Our patient was treated with a 5% benzoyl peroxide wash.
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Potential Conflicts of Interest: All authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
References
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