Subungual myxoid pleomorphic fibroma.

The authors report an example of pleomorphic fibroma in a unique site: the subungual space of the thumb. A 54-year-old man presented with paronychia and markedly thickened hyperkeratotic nail. The nail plate was removed, and an exophytic, red, friable, granulation tissue-like lesion was revealed subungually. The lesion was diagnosed clinically as pyogenic granuloma. Excisional biopsy was performed. Histologically, the lesion showed a hypocellular fibroma with myxoid areas and dilated blood vessels. Interspersed with ordinary appearing fibroblasts, there were bizarre, atypical fibroblasts with hyperchromatic and large, pleomorphic nuclei and multinucleated floret-like giant cells. These atypical cells showed strong immunoreactivity with antibodies against CD34 and vimentin. Occasional positivity was noted with factor XIIIa and alpha-1-antichymotrypsin, whereas no reactivity occurred with alpha-1-antitrypsin, actin, or S-100 protein. The entity of pleomorphic fibroma has been reported in many body sites; however, this is the first case to be reported in the subungual space.