Pilomatricoma With Melanocytic Hyperplasia: An Uncommon Occurrence and a Diagnostic Pitfall

To the Editor.—  Pilomatricoma is a benign neoplasm with differentiation toward hair matrix cells.¹ It manifests as a firm, deep-seated nodule on the face and upper extremities of individuals in the first two decades of life. Histologically, pilomatricoma is sharply circumscribed and displays basophilic, mitotically active, matrix cells and eosinophilic shadow cells. There is a gradual transition from matrix cells to shadow cells. Secondary features² include hemorrhage, dystrophic calcifications, ossification, and foreign body granulomatous reaction. Pigmentation due to melanin was observed in 8% of all cases in a large reported series.³ Dendritic melanocytes have also been observed in pigmented pilomatricomas.⁴

Report of a Case.—  A pilomatricoma with a unique, previously unreported overt melanocytic hyperplasia was observed. The lesion demonstrated areas with the aforementioned features of pilomatricoma (Fig 1). Other areas in the same lesion (Fig 2) showed an almost complete replacement of the matrix cells by