Pitted keratolysis is a skin disorder caused by certain Gram-positive bacteria such as Corynebacterium spp. Affected individuals typically present with foot odor and multiple small pits on weight-bearing parts of their soles. Treatment comprises a change of footwear as well as the topical application of antimicrobials. The condition is associated with an excellent prognosis.
Pitted keratolysis (PK) has been observed in patients of any age, in shod and unshod populations distributed throughout the world . Nevertheless, a thorough anamnesis often reveals that patients used to wear tight, poorly breathable shoes for prolonged periods of time. In this context, PK is more frequently diagnosed in soldiers, sailors and athletes . Furthermore, barefooted people in tropical areas are prone to develop PK. The afore-described conditions favor growth and replication of the causative agents of the disease. In more than 90% of cases, both feet are involved .
As its name implies, the disease is associated with progressive proteolysis in the stratum corneum, which results in the appearance of characteristic pits on the plantar surface. Circular lesions appear as if they have been punched out, and they may measure up to 7 mm in diameter . Coalescence of pits may result in larger, crateriform skin defects. Less profound lesions of distinct size may also be observed. Affected skin may take on a pale, whitish tone, or become erythematous. It may be traversed by fissures . Lesions are most commonly located on the heels and weight-bearing metatarsal parts of the feet, although the disease tends to spread over the forefoot and towards the toes. Many patients describe an apparent exacerbation when soaking their feet in water  while the accentuation of skin lesions does indeed result from a swelling of the infected, eroded stratum corneum.
PK patients usually seek medical attention because of profuse sweating, sliminess of affected feet and socially unacceptable foot odor  . Hyperhydrosis is, however, not a prerequisite for the diagnosis of PK. Some patients may claim an itching or burning sensation while walking, and the condition may also be associated with pain.
In rare cases, PK may also affect the palms of the hands  . Here, scaling may be more pronounced than in plantar PK.
PK is diagnosed clinically. The presence of multiple small pits on irritated, hyperhidrotic soles is considered pathognomonic of PK . The examination of affected skin with a Wood lamp typically reveals a pale yellowish or coral red fluorescence, but it has been pointed out that this is not an exclusion criterion  . Skin scrapings may be obtained for microscopic analysis. In the case of dermatomycosis like tinea pedis, treatment of specimens with potassium hydroxide should facilitate the observation of dermatophytes and spores. Of note, patients may suffer from PK and concomitant tinea pedis . If samples are taken for bacterial cultures, Gram-positive bacilli or coccobacilli (corresponding to Corynebacterium spp., Kytococcus sedentarius, or Dermatophilus congolensis) may be isolated  . Such procedures are rarely necessary, though. This also applies for the histopathological examination of biopsy specimens. If electron microscopy scanning is carried out for scientific purposes, hypokeratosis of the plantar skin and sweat gland ducts may be observed .