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Superficial acral fibromyxoma presenting as a haemorrhagic pigmented streak on the toenail

Superficial acral fibromyxoma (SAF) is a benign, slowgrowing, soft-tissue tumour that commonly affects the periungual and subungual regions of the fingers or toes. The tumour is painless, and can be dome-shaped, polypoid or verrucous in appearance. We describe a very unusual presentation of SAF. A 57-year old woman, with Fitzpatrick skin type VI, presented with a longstanding and asymptomatic pigmented streak of the right second toenail. She had originally been referred because of a burning sensation of the soles of her feet. She was otherwise well, with no relevant medical history. On physical examination, a pigmented streak, 5 mm in diameter, was seen, involving the lateral surface of the right second toenail (Fig. 1a,b). Hutchinson sign of the proximal nailbed was positive. There was evidence of haemorrhage at the distal end of the nail plate. An assessment of the toenail from the foot of the examination bed also revealed a thickened, verrucous subungual mass. Because of the clinical suspicion of melanoma, an urgent biopsy examination was performed. On histological examination, the nailbed was found to display basal hyperpigmentation and elongation of the rete ridges. A normal melanocytic population without atypia was seen. Unexpectedly, despite the clinical picture, no melanocytic lesion was identified. The underlying dermis contained a bland, spindle-cell lesion that had a poorly formed, mixed fascicular and storiform pattern with collagenous stroma (Fig. 2a). Scattered mast cells were present. Immunohistochemical studies showed the tumour to be positive for CD34 (Fig. 2b) and negative for S100, Melan A, desmin, smooth muscle actin and epithelial membrane antigen (EMA). There was no cytological atypia. The lesion was diagnosed as SAF. SAF was first described in a series of 37 cases by Fetsch et al. in 2001. Since then, < 50 cases have been reported in the literature, including lesions on the palm and sole. SAF is reported to be twice as common in male as in female patients. The mean age at presentation is 43 years, with a wide age range of 14–72 years. The size of the tumour varies from 6 to 50 mm, and typically extends throughout the entire dermis. Occasionally, the lesion may extend to involve the subcutis. Histologically, there is a moderately cellular proliferation of spindled fibroblast-like and stellate-shaped cells, embedded in a myxoid and ⁄ or collagenous matrix in the dermis. The epidermis may be hyperkeratotic. Mitotic figures are rare, and cytological atypia is usually mild. Mast cells are readily identified. Tumour cells stain positive for CD34, CD99 and vimentin. There is variable immunoreactivity to EMA and recently, expression of CD10 was found in three of four cases reported by Tardio et al. The myxoid matrix within SAF is highlighted using Alcian blue (pH 2.5) stain. We highlight the fact that SAF can present as a pigmented lesion, something we believe has not been previously described in the literature. Surgical excision is the treatment of choice in symptomatic patients. Reassuringly, there have been no reports of malignant transformation.