A Novel Visual Clue for the Diagnosis of Hypertrophic Lichen Planus

Dermatology has an illustrious history of formulating visual clues to facilitate diagnosis of oft-confused conditions. From the opulent (“crown-of-jewels”) to the mundane (“apple jelly”), dermatologists have consistently drawn inspiration from the physical world when classifying disease. We intend to add to this literature by submitting a novel visual clue to aid in the diagnosis of hypertrophic lichen planus.

Given a causal linkage with the hepatitis C virus and recent case reports of malignant transformation, hypertrophic lichen planus requires astute and careful consideration.^{1 - 2} The condition is marked by firm, elevated, hyperkeratotic, red-brown to purple-gray plaques with chalky-white scale and follicular accentuation that imparts a geologic appearance to affected skin (Figure 1). Lesions thus bear a striking resemblance to the extrusive (or rapidly cooled) variants of igneous rock (Figure 2), characterized by a fine-grained (or aphanitic) texture with the occasional vesicular (pocked) surface and variable colors from dark pink to gray-black.^{3 - 4} The igneous rock sign has been a useful adjunct in several cases (Figure 3) to help differentiate hypertrophic lichen planus from other members of the papulosquamous differential, and we hope that it becomes a valued visual clue in the armamentarium against dermatologic disease.