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.