Melanocytic and pseudomelanocytic nests coexist in interface dermatitis from head-neck sun-exposed skin: A report of three cases.

Discrete junctional cellular aggregates ("nests"), partially staining with melanocytic markers, are described in lichenoid tissue reaction, mainly from chronically sun-exposed skin. The concomitant epidermal flattening and papillary dermal fibrosis with melanophages, may raise the differential diagnosis to that of a regressing melanoma. We describe three cases of interface dermatitis of the head/neck area with clinicopathological features of melanotic discoid lupus erythematosus. These cases showed junctional aggregates, a few composed of inflammatory cells and colloid bodies ("pseudomelanocytic nests"), while others composed of S100- but MART-1+, MITF+, and SOX-10+ cells ("true melanocytic nests"); negativity of the melanocytic component for PRAME was a clue to benignity. True junctional melanocytic nesting may be induced by lichenoid dermatoses on chronically sun-damaged skin. The presence of colloid bodies and of the double negativity for S100 (within nests) and PRAME (both within nests and single melanocytes), together with clinicopathological correlation, avoids misdiagnosis.