The Diagnosis: Superficial Acral Fibromyxoma
Figure 1. Plainradiographic evidenceof inferior corticallucency on the leftgreat toe.
Superficial acral fibromyxoma (SAF) was first described in 2001 by Fetsch et al.1 Subsequently, the term digital fibromyxoma was proposed in 2012 by Hollmann et al2 to describe a distinctive, slow-growing, soft-tissue tumor with a predilection for the periungual or subungual regions of the fingers and toes. The benign growth typically presents as a painless or tender nodule in middle-aged adults with a slight male predominance (1.3:1 ratio).1,2 In a case series (N=124) described by Hollmann et al,2 9 of 25 patients (36%) who had imaging studies showed bone involvement by an erosive or lytic lesion. Reports of SAF with bone involvement also have been described in the radiologic and orthopedic surgery literature.3,4 Radiographically, the soft-tissue invasion of the bone is demonstrated by scalloping on plain radiographs (Figure 1).3
Histologically, SAFs are moderately cellular with spindled or stellate fibroblastlike cells within a myxoid or collagenous matrix (Figure 2).1 The vasculature is mildly accentuated and an increase in mast cells usually is observed. The nuclei have a low degree of atypia with few mitotic figures, and the stellate cells exhibit positive immunohistochemical staining for CD34 (Figure 3), epithelial membrane antigen, and CD99.1 Hollmann et al2 found that 66 of 95 tumors (69.5%) infiltrated the dermal collagen, 26 (27.4%) infiltrated fat, and 3 (3.2%) invaded bone. Of the 47 cases that were evaluated on follow-up, 10 tumors (21.3%) recurred locally (all near the nail unit of the fingers or toes) after a mean interval of 27 months. Although invasion of underlying tissues and recurrence of the tumor has been demonstrated, this growth is considered benign. The histologic differential diagnosis includes neurofibroma, myxoma, fibroma, low-grade fibromyxoid sarcoma, dermatofibroma, superficial angiomyxoma, and dermatofibrosarcoma protuberans.2
The primary treatment of SAF is local excision. The incidence of local recurrence found in the case series by Hollmann et al2 was directly linked to positive margins after the first excision (10/47 [21.3%] recurrent lesions had positive margins). To date, there are no known reports of metastatic disease in SAF.2 Our case manifested with a late recurrence of the tumor and bone involvement requiring surgical excision, which illustrates the role of adjuvant imaging and close follow-up following excision of any soft-tissue tumors of the fingers and toes that have been histologically confirmed as SAF, particularly those of the periungual region.
 Figure 2. Benign epidermis with a low-grade myxoid dermis (H&E, original magnification ×4). Reference bar denotes 600 μm. |
 Figure 3. Higher magnification of the myxoid stroma and CD34 positivity (original magnification ×7.4). Reference bar denotes 300 μm. |