Common and plantar warts with trichilemmal keratinization-like keratinizing process: a possible existence of pseudo-trichilemmal keratinization.

Thirty-one common and five plantar warts were investigated histopathologically and electron microscopically in order to reveal whether or not these warts keratinize in a fashion similar or identical to trichilemmal keratinization (TK). Histopathologically, parts of 12 of 31 common, and 3 of 5 plantar warts, exhibited varying keratinization similarities to TK. The most similar case showed changes almost identical to intrinsic TK. Electron microscopy revealed uneven and somewhat interdigitating borders between the keratinized and the keratinizing cells, with a few ladder-like membrane coating granules. It is postulated that there may be TK or TK-like keratinization without any relationship to the outer root-sheath of the hair follicle. We propose the concept of pseudo-TK to distinguish this type of keratinization from intrinsic TK.