Ultrastructure of pitted keratolysis

A 20‐year‐old man presented with pitted keratolysis (PK), demonstrating the typical crateriform pits on the hallux ( Fig. 1), ball of the foot, and on the interdigital surface. The involved keratin specimen was obtained by a shaving technique and processed for transmission (TEM) and scanning (SEM) electron microscopy. The patient, who wore only sports shoes, had hyperhidrosis plantaris. He was treated with topical erythromycin with good results. Bacterial cultures from the lesions showed Corynebacterium sp. 1Crateriform pits on the hallux TEM demonstrated filamentous coccoid bacteria in the keratin ( Fig. 2), showing transversal septations. Tunnel‐like spaces were built inside the horny layer, where the bacteria showed a hairy surface ( Fig. 3). 2Bacteria inside the stratum corneum (TEM, × 25,000)3Hairy surface from the causative agent (TEM, × 106,000) Crateriform pits ( Fig. 4) and small incipient lesions ( Fig. 5) were easily identified on the plantar surface by SEM. On examination of the floor of these lesions, tunnel openings were found ( Fig. 6) in which bacteria could be observed. With higher magnification, the transversal septation, seen by TEM, was also shown with SEM ( Fig. 7). The normal appearing plantar skin was also examined, showing incipient bacterial colonies with tunnels without keratin loss ( Fig. 8). 4Pitted keratolysis with two incipient lesions on the right side (SEM, × 77.5)5Higher magnification of the incipient lesion from the right upper corner of Fig. 4 (SEM, × 310)6Tunnel openings in the floor of the pits (SEM, × 15,500)7Details of the bacteria; note the transversal septation (SEM, × 31,000)8The causative agent in tunnels in normal appearing skin (SEM, × 4650)