Proliferative Neurocristic Hamartoma Arising From a Congenital Melanocytic Nevus: A Case Report

Proliferative neurocristic hamartoma (PNH), a rare variant of proliferative nodule, is a benign cutaneous proliferation with melanocytic, neurosustentacular, and mesenchymal differentiation that develops within a congenital or acquired melanocytic nevus. We report the case of a 38-year-old female who presented with a brownish-black plaque on the right medial sole that appeared during childhood and showed rapid nodular growth in the center over the past year. Histological examination revealed a well-demarcated dermal nodule characterized by spindle cell proliferation in a haphazard pattern in the center, with a congenital melanocytic nevus in the periphery. Immunohistochemical staining for S-100, SOX-10, HMB45, EMA, Glut-A, and CD34 demonstrated melanocytic, perineural, and fibrous differentiation in the central nodule, consistent with PNH. The mitotic activity was very low for the Ki-67 stain, and the PRAME stain was negative. Accurate pathological diagnosis is essential to reassure the patient of the nature of this changing mole and exclude the possibility of melanoma.