Pitted keratolysis

What is pitted keratolysis?

Pitted keratolysis is a descriptive title for a superficial bacterial skin infection that affects the soles of the feet, and less often, the palms of the hands. It is one of the causes of smelly feet. It is characterised by whitish skin and clusters of punched-out pits.

Image provided by Dr S Janjua

What is the cause of pitted keratolysis?

Pitted keratolysis is caused by several bacterial species, including corynebacteria, Dermatophilus congolensis, Kytococcus sedentarius, actinomyces and streptomyces.

The bacteria proliferate in moist conditions. The pitting is due to destruction of the horny cells (stratum corneum) by protease enzymes produced by the bacteria.

The bad smell is due to sulfur compounds produced by the bacteria: thiols, sulfides and thioesters.

Who's at risk of pitted keratolysis? 

 Pitted keratolysis is much more common in males than in females. Occupations at risk include:

• Farmers
• Athletes
• Sailors or fishermen
• Industrial workers
• Military personnel  

Females offering pedicure and foot care in a spa salon may also be affected by pitted keratolysis. 

Factors that lead to the development of pitted keratolysis include:

• Hot, humid weather
• Occlusive footwear, such as rubber boots or vinyl shoes
• Excessive sweating of hands and feet (hyperhidrosis)
• Thickened skin of palms and soles (keratoderma)
• Diabetes mellitus
• Advanced age
• Immunodeficiency 

What are the signs and symptoms of pitted keratolysis?

Pitted keratolysis:

The result is very smelly feet, due to infection of the soles. Either the forefoot or the heel or both become white with clusters of punched-out pits. The appearance is more dramatic when the feet are wet. Very rarely, the fingers are similarly affected. There is a variant of pitted keratolysis where there are more diffuse red areas on the soles.

• Mostly affects the soles, forefoot, the heel or both. Palms are rarely infected.
• Results in a whitish skin surface with clusters of multiple, fine punched-out pits.
• Pits often join together (coalesce) to form larger, crater-like lesion.
• A variant of pitted keratolysis presents with diffuse red areas on the soles. 

The most commonly reported symptom is malodour. The pits themselves are usually asymptomatic but may cause soreness or itching when walking. 

Image provided by Dr S Janjua

How is the diagnosis of pitted keratolysis made?

Pitted keratolysis is usually diagnosed clinically. Swabs are rarely required. However, the causative organisms may be identified from the pitted lesions and cultured on brain heart infusion agar.

Skin scrapings are often taken to exclude fungal infection. Wood light examination displays a characteristic coral red fluorescence in some cases.  

The diagnosis is sometimes made by skin biopsy revealing characteristic histopathological features of pitted keratolysis.

Treatment of pitted keratolysis

Pitted keratolysis can be successfully treated with topical antibiotics and antiseptics including:

• Erythromycin
• Clindamycin
• Mupirocin
• Fusidic acid
• Benzoyl peroxide

Oral erythromycin is also helpful.   

How can pitted keratolysis be prevented?

Pitted keratolysis will quickly recur unless the feet are kept dry. The following precautions should be taken to prevent recurrences:

• Wear boots for as short a period as possible
• Wear socks which effectively absorb sweat, ie cotton and/or wool
• Wear open-toed sandals whenever possible
• Wash feet with soap or antiseptic cleanser twice daily
• Apply antiperspirant to the feet at least twice weekly
• Do not wear the same shoes two days in a row — dry them out
• Do not share footwear or towels with others. 

Wear boots for as short a period as possible

• Wear socks which effectively absorb sweat i.e. cotton and/or wool
• Wear open-toed sandals whenever possible
• Wash feet with soap or antiseptic cleanser twice daily
• Apply antiperspirant to the feet at least twice weekly
• Do not wear the same shoes two days in a row – dry them out
• Do not share footwear or towels with others.