Oral hairy leukoplakia with ultrastructural evidence of Merkel-like cells in human tongue epithelium.

The purpose of this investigation was to examine cells in the stratum basale and subjacent lamina propria of oral hairy leukoplakia (OHL) specimens for previously unreported morphological changes. Tongue biopsy specimens were obtained from ten HIV-positive and five healthy male patients and examined by light (LM) and transmission electron microscopy (TEM). Observations made during the investigation revealed the following: (1) LM comparisons of control and OHL specimens indicated that clear cells in the stratum basale ranged from 3 to 7 per 100 basal epithelial cells in healthy tongue mucosa vs. 6 to 15 in OHL. (2) Merkel-like cells were noted in the stratum basale of control biopsies from the dorsal-lateral tongue surface. However, the frequency of observation was so rare as to imply that their presence was an exception rather than the norm. (3) In contrast, Merkel-like cells in OHL specimens were commonly encountered, indicating a possible unique relationship to the pathology. (4) Merkel-like cells associated with OHL lesions were morphologically similar, in all respects, to that of control specimens except for the presence of large, membrane bound, dense granules that ranged in size from 150-300 nm. (5) All biopsies of OHL exhibited evidence of Epstein Barr virus in the stratum corneum and superficial layers of the stratum spinosum. (6) A mild inflammatory infiltrate associated with OHL specimens revealed cytopathic changes in fibroblasts that appeared related to the presence of lymphoid cell types; indicating a possible cytolytic lymphocyte-mediated degradation of antigen altered host cells.