Lichenoid solar keratosis--prevalence and immunologic findings.

Solar keratoses (SKs) may show basal cell liquefactive degeneration (BLD) and, when extensive, this can result in a superficial resemblance to lichen planus. The frequency of these phenomena and involvement of immune mechanisms in them have been investigated in this study. The prevalence of lichenoid keratosis (LK) was 6.1% in 212 SKs examined retrospectively and 10.7% in 28 examined prospectively. Histologic features were scored on analogue scales and their interrelationships examined. BLD could not be correlated with epidermal atypia, acanthosis, acantholysis, or inflammatory cellular infiltrate; a negative correlation occurred with parakeratosis. Immunoglobulins and/or fibrin and complement were found by immunofluorescence in 78.8% of the 28 specimens examined prospectively. Three LKs showed similar immunofluorescence findings to ordinary SKs. No circulating antibodies to epidermal structures were detected in patients with SKs. It is concluded that (1) no feature of SKs investigated predisposed to lichenoid change, (2) BLD was a frequent feature in SKs whereas full development of LK occurred much less frequently, and (3) immunoprotein deposits were not related to the development of BLD. Clinically, LKs could not be distinguished from ordinary SKs.