Answer: Oral hairy leukoplakia

Histology: The squamous epithelium is characterized by irregular zones of parakeratosis. The corrugated surface is colonized by bacterial organisms. The upper spinous layer underlying the patches of parakeratosis shows “balloon cell” change. At high magnification, some of the balloon cells exhibit peripheral marginization of chromatin, sometimes referred to as “nuclear beading”. An in-situ hybridization assay (i.e. EBER) for the Epstein-Barr virus (EBV) demonstrates a strong hybridization signal in the nuclei of the balloon cells.

Discussion: Oral hairy leukoplakia (OHL) is an EBV-related lesion of the oral cavity that is usually encountered in immunosuppressed individuals, particularly in individuals with HIV/AIDS. It is usually noted along the lateral border of the tongue as a thickened leukoplakia with a shaggy surface. The histopathologic findings including parakeratosis, balloon cell change and nuclear beading are quite characteristic of OHL, but they are not entirely specific. The diagnosis can be confirmed by demonstrating the presence of EBV. OHL is a benign process, and lesions resolve with EBV therapy such as acyclovir. Lesions also regress with HIV therapy. The diagnosis of OHL in a “normal” patient necessitates a medical evaluation of immunologic status including HIV status.

Hairy black tongue is confused with OHL more in name than by histologic features. Hairy black tongue does show zones of profound hyperkeratosis, but it lacks the balloon cell change and other morphologic features of OHL. Unlike OHL, hairy tongue is not caused by EBV.