Pitted Keratolysis: New Ultrastructural Insight in Keratohyalin Granule and Corneodesmosome Alterations

Background: Pitted keratolysis (PK) is a superficial cutaneous infection caused by different species of bacteria. It is characterized by discrete crateriform and malodorous pits and erosions coalescing to form bizarre figures on the soles. Objective: To investigate the process of corneocyte shedding in PK. Method: Biopsies from typical lesions of 3 patients were investigated by transmission electron microscopy. Results: Microorganisms were found both inter- and intracellularly in corneocytes and keratinocytes of the upper layers of the stratum spinosum. Bacteria exhibited different morphologic aspects related to their localization in the epidermis. Keratohyalin granules were strikingly abnormal, showing sharp segregation between rounded dense areas and more electron-translucent areas. Some keratohyalin granules exhibited only alveolar dense areas. These altered keratohyalin granules were still present inside corneocytes. The corneodesmosomes at the bottom of the pits were in part cleaved leading to partial corneocyte dissociation. Conclusion: It is suggested that proteases secreted by the bacteria alter the structure of both the corneodesmosomes and the keratohyalin granules. The latter appeared more resistant to the normal processing of profilaggrin inside the corneocytes.