Pitted keratolysis: causes, symptoms, diagnosis, and treatment

Pitted keratolysis, also known as keratolysis plantare sulcatum, keratoma plantare sulcatum, or ringed keratolysis, is a bacterial infection in the stratum corneum of the soles, more common in tropical and subtropical areas, mostly in persons in close and long term contact with soil and water, and is characterized by ringed or pitted erosion of the stratum corneum of the soles, without subjective symptoms.


Causes

The pathogenic bacteria of this disease cannot be completely determined to date. It has been reported that Actinomycetes, Nocardia, Trichophyton mentagrophytes, Streptomyces, and Mycobacterium can cause the disease. Corynebacterium has been found in the bacterial culture in patients. It is currently speculated to be a synergistic effect of Corynebacterium and Streptomyces. Warm and humid environments are necessary for the onset.


Signs and Symptoms

The clinical manifestations are the stratum corneum thickening of the soles, especially the anterior soles, heels, and lateral toes. Pale brown or dirty skin on the soles is usually present. Some pinhead sized, crateriform, shallow pits often irregularly and densely forms into a honeycomb, and sometimes fuses into patches or multiple rings, with moth-eaten edges. In severe cases, striped grooves on the heel edges may be present. Pitted, patchy, and striped depressions can be concurrent, and are limited to the hyperkeratotic stratum corneum, without inflammation and subjective symptoms. The skin lesions are skin colored, brown, black, and even green. Mild tenderness may be present in patients with severe skin lesions when walking for a long time. A small number of patients have keratin pits on the dorsal toes, dorsal feet, and even palms. Intertoe maceration and erosion may occur in patients with hyperhidrosis.


Histopathology

Localized defects in the upper stratum corneum, generally not more than 2/3 of the thickness of the stratum corneum, are visible. Homogenization of the stratum corneum around the defects is present. Gram-positive spherical and filamentous bacteria can be seen in the base and wall of the defects. Mild inflammatory reaction in the dermis can be seen.


Diagnosis

According to the typical clinical presentations, diagnosis is not difficult.


Treatment

After keeping the feet dry and leaving the hot and humid environment, the disease can gradually heal spontaneously.

The common treatment is erythromycin 0.25g orally 4 times a day for 1 week. Topical fusidic acid ointment, tetracycline ointment, azoles, 5% benzoyl peroxide cream, and 40% formalin ointment have obvious effects. If with excessive sweating, topical 20% - 40% formalin solution or 10% - 20% aluminum chloride solution can be used.