Pitted Keratolysis

Pitted keratolysis is a superficial bacterial infection of the plantar stratum corneum, caused by Kytococcus sedentarius, Corynebacterium species and Dermatophilus congolensis, which digest keratin and produce sulfur compounds. It is common in people with sweaty feet, occlusive footwear, agricultural or military occupations, and those living in hot humid climates.

• Risk factors: hyperhidrosis, prolonged wet footwear, barefoot walking in muddy conditions, diabetes, obesity.

Multiple 1 to 3 mm punched out pits in the thickened plantar skin, particularly at pressure points (heel, ball of foot, toes), sometimes coalescing into erosions.

• Foul odour, moist macerated skin, mild tenderness; often asymptomatic apart from smell.
• Differential diagnosis: plantar warts, tinea pedis, palmoplantar keratoderma, basal cell naevus syndrome, arsenical keratosis, erythrasma, punctate porokeratosis, secondary syphilis.
• Complications: secondary infection, chronic odour and social embarrassment, spread to hands (rare), recurrence.

Clinical; smell and pits are characteristic.

• Gram stain or culture only for resistant cases.
• Wood lamp may exclude erythrasma (coral red).
• Glucose if recurrent or diabetes suspected.

Reduce moisture and apply a topical antibacterial.

• Supportive: change socks twice daily (cotton or moisture wicking), rotate and air footwear, wash feet daily with antibacterial soap and dry thoroughly, avoid occlusive shoes and prolonged wet boots.
• Pharmacological: clindamycin 1 percent lotion or gel twice daily for 4 weeks; erythromycin 2 percent gel twice daily for 4 weeks; mupirocin 2 percent ointment three times daily for 2 weeks; fusidic acid 2 percent cream three times daily for 2 weeks; benzoyl peroxide 5 percent wash daily. For hyperhidrosis: aluminium chloride hexahydrate 20 percent solution at night. Extensive or recurrent disease: erythromycin 500 mg four times daily for 2 weeks, or doxycycline 100 mg twice daily for 2 weeks.
• Procedures: iontophoresis or botulinum toxin for refractory plantar hyperhidrosis.
• Special groups: pregnancy, topical clindamycin or mupirocin only; children, topical erythromycin or clindamycin and drying; diabetes, careful foot care; doxycycline contraindicated under 8 years and in pregnancy.
• Red flags: spreading cellulitis, ulceration, fever, severe pain, diabetic foot involvement.
• Follow-up: review at 4 weeks; advise ongoing foot hygiene and footwear change.