Rare Palisading Variant of Dermatofibroma

Dermatofibromas (DFs) are benign lesions that typically present as firm papules or nodules on the legs of young- to middle-aged adults. DFs are histologically characterized by a dermal proliferation of spindled fibrohistiocytic cells forming intersecting fascicles and showing collagen entrapment. The palisading variant of DF was first described in 1986 and often presents as a dome-shaped nodule on the digits. Histologically, palisading DFs demonstrate central areas of nuclear palisading in parallel rows resembling Verocay bodies, with more typical areas of DF located peripherally. We report a case of a 33-year-old Hispanic woman who presented with a history of an asymptomatic, slow-growing lesion on her left arm present since her teenage years. Physical examination revealed a solitary, firm brown-to-white 5-mm papule on the left upper arm. A biopsy was performed and revealed a proliferation of spindle cells palisading around areas of hyalinized collagen. The many histologic variants of DF can sometimes create diagnostic confusion. Previously described cases of palisading DFs in the literature showed palisading resembling Verocay bodies and thus raising concern for a schwannoma or other neoplasm that display a "rippled" pattern. Our case is unique in that the architecture of the palisading areas instead resembled a necrobiotic granulomatous process such as granuloma annulare or a rheumatoid nodule at low power.