Atypical pilar leiomyoma: cutaneous counterpart of uterine symplastic leiomyoma?

Four cases of cutaneous leiomyoma with cytologic atypia are reported. All four cases were adult men ranging in age from 33 to 92 years of age. Clinical diagnoses were diverse and included epidermal inclusion cyst, scar, nevus, dermatofibroma, squamous cell carcinoma, and basal cell carcinoma. Histological examination of all four lesions revealed a relatively circumscribed, mild to focally moderately cellular, dermal proliferation of large, irregularly shaped spindle cells in a fascicular arrangement. Some cells contained large irregular nuclei and abundant cytoplasm; others were multinucleate. Moderate to focal marked pleomorphism and rare mitotic figures were present, raising the possibility of leiomyosarcoma; however, the sparse mitotic activity and low cellularity did not warrant this diagnosis. This study suggests that cutaneous leiomyomas may exhibit bizarre or "symplastic" patterns analogous to their uterine counterparts.