Background
Pitted keratolysis is a skin disorder characterized by crateriform pitting that primarily affects the pressure-bearing aspects of the plantar surface of the feet and, occasionally, the palms of the hand as collarettes of scale. It is typically asymptomatic and associated with malodor. [1] Its manifestations are due to a superficial cutaneous bacterial infection. [2, 3]
Pitted keratolysis has gone through several name changes. It was initially described in the early 1900s as keratoma plantare sulcatum, a manifestation of yaws. The condition was then identified as a unique separate clinical entity in the 1930s, at which time it came to be referred to as keratolysis plantare sulcatum (or keratolysis sulcata). The current name, pitted keratolysis, describes the clinical presentation well and has become the preferred modern nomenclature.
Pathophysiology
Pitted keratolysis is caused by a cutaneous infection with Kytococcus sedentarius (formerly Micrococcus sedentarius), Dermatophilus congolensis, Bacillus thuringiensis, [4] or species of Corynebacterium,Actinomyces, or Streptomyces.
Under appropriate conditions (eg, prolonged occlusion, hyperhidrosis, and increased skin surface pH), these bacteria proliferate and produce proteinases that destroy the stratum corneum, creating pits. D congolensis liberates keratinases in appropriate substrates. [5, 6] K sedentarius has been found to produce two keratin-degrading enzymes: protease P1 (30 kd) and protease P2 (50 kd). [7] The malodor associated with pitted keratolysis is presumed to be the production of sulfur-compound by-products, such as thiols, sulfides, and thioesters. [8]
In 2006, foot odor without pitted skin changes was discovered to be from overgrowth of Bacillus subtilis and specifically from an isovaleric acid produced by overgrowth of Staphylococcus epidermidis, a normal skin organism. [9]
It is a common problem among athletes, as heat, sweat, and humidity cause changes in the skin microbiome. [10, 11, 12]
Epidemiology
US and international statistics
Pitted keratolysis occurs worldwide. It can be seen in both tropical and temperate environments, and it can be related to occupation or sport activity. [13, 14] A study of 142 homeless men in the Boston, MA, area revealed that 20.4% of 142 examined patients had pitted keratolysis. [15]
Internationally, the frequency with which pitted keratolysis is found has varied significantly, depending on environment and occupation. The prevalence of pitted keratolysis was reported to be 1.5% in 4325 Korean industrial workers [16] and 2.25% in 490 randomly evaluated subjects from New Zealand. [17] In another study, 2.6% of 378 Turkish male adolescent and postadolescent boarding school students had pitted keratolysis, [18] and a 2-year study from Belgium identified only 4.8 cases of pitted keratolysis per 1000 dermatology visits. [19]
In a study of 1012 patients with atopic dermatitis from Nigeria, only 19 (1.8%) had pitted keratolysis. [20] In other studies, however, 66 (23.3%) of 283 Korean coal miners [16] and 145 (42.5%) of 341 paddy field workers in coastal South India had pitted keratolysis due to persistent exposure to moist environments. [21] In a study of 230 paddy field workers in northern India who had skin lesions, 16.5% of the workers had pitted keratolysis. [22] In a study of 184 German athletes, 25 (13.5%) had pitted keratolysis. [10]
In tropical military settings, where heat, humidity, and boots combine to produce a microenvironment that predisposes to pitted keratolysis, the frequency is much higher. In a study evaluating 387 volunteer US soldiers in South Vietnam, 53% had pitted keratolysis. [23] However, the incidence of pitted keratolysis may not be so high in all soldiers. In a study of 842 Korean soldiers, only 108 (12.8%) were diagnosed with pitted keratolysis. [24]
Age-, sex-, and race-related demographics
Pitted keratolysis can affect patients of any age. Theoretically, both males and females should be affected by pitted keratolysis; however, most written case reports or studies have involved male patients. No race predilection is reported for pitted keratolysis.
Prognosis
Pitted keratolysis is easily cured and has an excellent prognosis. It is not associated with any mortality; however, the excessive foot odor from this disorder may be socially unacceptable. Pitted keratolysis may be symptomatic in some cases, producing secondary foot pain, which can limit function. [25]
In a 2005 study from Turkey (East region) that examined dermatologic manifestations in 88 hepatitis B surface antigen (HBsAg) carriers as compared with 84 control subjects, a significantly higher prevalence of oral lichen planus and pitted keratolysis was demonstrated in HBsAg carriers. [26] The mechanism was unknown, and further studies would be needed to confirm this association.
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Large plaquelike lesion of pitted keratolysis on great toe.
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Case of inflammatory pitted keratolysis.
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Pitted keratolysis with hyperkeratosis on heel.
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Classic pits of pitted keratolysis on plantar aspect of phalanges.
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Pitted keratolysis forming sulci on heel.
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Histopathology reveals crater limited to thick stratum corneum of epidermis.
