Chapter 118. Pitted Keratolysis

A 34-year-old man comes to the office with a terrible foot odor problem. He is wearing cowboy boots and he says that his feet are always sweaty. He is embarrassed to remove his boots, but when the physician convinces him to do so the odor is overwhelming. While breathing through the mouth, the physician sees the typical pits of pitted keratolysis. His socks are moist and the skin is somewhat macerated from the hyperhidrosis. His foot has many crateriform pits on the heel (Figure 118-1). He is prescribed topical erythromycin solution for the pitted keratolysis and topical aluminum chloride for the hyperhidrosis. It is suggested that he wear a lighter and more breathable shoe until this problem improves.

Pitted keratolysis is a superficial foot infection caused by Gram-positive bacteria. These bacteria degrade the keratin of the stratum corneum leaving visible pits on the soles of the feet.

• Seen more commonly in men.
• Often a complication of hyperhidrosis.
• Seen more often in hot and humid climates.
• Prevalence can be as high as 42.5% among paddy field workers.1
• May be common in athletes with moist, sweaty feet.2

• Kytococcus sedentarius (formerly Micrococcus spp.), Corynebacterium species, and Dermatophilus congolensis have all been shown to cause pitted keratolysis.3
• Proteases produced by the bacteria degrade keratins to give the clinical appearance.4
• The associated malodor is likely secondary to the production of sulfur byproducts.3

Clinical Features

Pitted keratolysis usually presents as painless, malodorous, crateriform pits coalescing into larger superficial erosions of the stratum corneum (Figures 118-1, 118-2, 118-3, 118-4). It may be associated with itching and a burning sensation in some patients (Figure 118-3).

Typical Distribution

Pitted keratolysis usually involves the callused pressure-bearing areas of the foot, such as the heel, ball of the foot, and plantar great toe. It can also be found in friction areas between the toes.5

Laboratory Studies

Typically a clinical diagnosis but biopsy will reveal keratin pits lined by bacteria.

• Characteristic clinical features make the diagnosis easy, but it is possible to have other diseases causing plantar pits, which can be included in the differential. These other diseases include plantar warts, basal cell nevus syndrome, and arsenic toxicity.
• Plantar warts are typically not as numerous. They have a firm callus ring around a soft core with small black dots from thrombosed capillaries (see Chapter 134, Plantar Warts).
• Basal cell nevus syndrome typically has pits involving the palms and soles, bone abnormalities, a history of many basal cell carcinomas, and a characteristic facies with frontal bossing, hypoplastic maxilla, and hypertelorism (wide-set eyes) (see Chapter 170, Basal Cell Carcinoma).
• Arsenic toxicity can result in pits on the palms and soles, but it can also have hyperpigmentation, many skin cancers, Mees lines (white lines on the fingernails), or other nail disorders.

• Treatment is based on bacterial elimination and reducing the moist environment in which the bacteria thrive. Various topical antibiotics are effective for pitted keratolysis.
• Topical erythromycin or clindamycin solution or gel can be applied twice daily until the condition resolves. SOR C Generic 2% erythromycin solution with an applicator top is a very inexpensive and effective preparation. It may take 3 to 4 weeks to clear the odor and skin lesions.
• Topical mupirocin is more expensive but also effective. SOR C
• Oral erythromycin is effective and may be considered if topical therapy fails. SOR C
• Treating underlying hyperhidrosis is also important to prevent recurrence. This can be done with topical aluminum chloride of varying concentrations. SOR C Drysol is 20% aluminum chloride solution and can be prescribed with an applicator top.
• Botulinum toxin injection is an expensive and effective treatment for hyperhidrosis.6 SOR C It should be reserved for treatment failures because of the cost, the discomfort of the multiple injections, and the need to repeat the treatment every 3 to 4 months.

Follow-up is needed for treatment failures, recurrences, and the treatment of underlying hyperhidrosis if present. Follow-up can be performed annually for prescription aluminum chloride or approximately every 4 months for botulinum toxin injections.

Patients should be taught about the etiology of this disorder to help avoid recurrence. Helpful preventive strategies include avoiding occlusive footwear and using moisture-wicking socks or changing sweaty socks frequently.

Patient Resources

• International Hyperhidrosis Society—http://www.sweathelp.org.

Provider Resources

• Medscape. Pitted Keratolysis—http://emedicine.medscape.com/article/1053078-overview.