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Abstract

Symplastic leiomyoma was first reported as a variant of uterine leiomyoma with nuclear pleomorphism, low mitotic figure count, and no tumoral necrosis. While originally classified as having intermediate malignant potential, further studies have described benign behavior. Symplastic variants of pilar leiomyomata have been described as a tumor of the skin. Herein we report a case of this rare cutaneous tumor. A 64-year-old male patient presented to the dermatology clinic with a 1 cm plaque on the right buttock. The plaque had grown slowly over several years and was tender to palpation. A punch biopsy was obtained, revealing a spindled fascicular neoplasm with prominent nuclear pleomorphism. There were no mitotic figures identified. The spindled cells exhibited positive staining for desmin and SMA. A diagnosis of symplastic leiomyoma was rendered. Symplastic variants of pilar leiomyomata are a rare cutaneous neoplasm with striking histopathology. Differentiation from malignant cutaneous neoplasm including atypical intradermal smooth muscle neoplasm (AISMN) is important due to prognostic implications. While symplastic leiomyoma may exhibit cytologic atypia, it lacks the high mitotic activity (< 2 mitoses) and necrosis commonly observed in AISMN.