Involucrin as a diagnostic marker in oral lichenoid lesions.

Thirty-eight biopsy specimens were examined for involucrin reactivity by an immunoperoxidase technique. The sampling consisted of specimens diagnosed as normal oral mucosa, reactive epithelial hyperplasia, lichen planus (LP), nonspecific lichenoid stomatitis (NLS), lichenoid dysplasia (LD), carcinoma in situ, and squamous cell carcinoma (SCCa) on routine hematoxylin and eosin examination. Findings were consistent with prior observations of involucrin reactivity in skin and cervical-vaginal mucosa. Specifically, conditions characterized by predominance of mature squamous epithelial cells (superficial layers of normal and hyperplastic oral epithelium, NLS, and LP) exhibited strong involucrin reactivity in such areas. In contrast, atypical or dysplastic lichenoid lesions (LD), as well as carcinoma in situ, despite squamoid differentiation, demonstrated irregular distribution of involucrin, suggesting disturbances in terminal differentiation. Invasive components of SCCa revealed markedly diminished involucrin expression. These findings support prior evidence that LP and LD are biologically distinct lesions. Clinically and microscopically, both may be morphologically similar. However, involucrin reactivity should be helpful in distinguishing difficult cases. Accordingly, we suggest that the use of involucrin immunoreactivity may prove to be a valuable adjunct in the separation of similar lichenoid oral conditions.