Symplastic Leiomyoma | Dermatopathology

Cutaneous leiomyomas are benign mostly solitary smooth muscle tumors occurring over a wide age range (33-92 years) in both men and women. The lesions can vary in size from 0.5 to >4 cm and appear as papules or plaques on the chest, back and extremities. They may infrequently display cytologic atypia similar to symplastic leiomyomas of the uterus. These atypical/symplastic leiomyomas feature increased cellularity, nuclear atypia, pleomorphism and rare or no mitoses. Reference: Cook et al. Atypical pilar leiomyomatosis: an unusual presentation of multiple atypical cutaneous leiomyomas. J Cutan Pathol 2013: 40: 564-568.

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Slide 1: 65 year-old woman with a tan firm papule on the thigh. R/O dermatofibroma.

Slide 2: A proliferation of spindled cells is noted within the dermis.

Slide 3: The cells assume a vesicular growth pattern whereby the fascicles do intersect in varying directions.

Slide 4: Overall, the cells lack significant atypia and mitotic activity.

Slide 5: However, there are randomly disposed atypical cells present throughout the lesion. The tumor is highlighted by SMA, desmin, caldesmon, and calponin; the proliferation index is low (i.e. <5%).