Superficial Acral Fibromyxoma and Other Slow-Growing Tumors in Acral Areas

First described by Fetsch et al¹ in 2001, superficial acral fibromyxoma (SAFM) is a rare fibromyxoid mesenchymal tumor that typically affects the fingers and toes with frequent involvement of the nail unit. It is not widely recognized and remains poorly understood. We describe a series of 3 cases of SAFM encountered at our institution and provide a review of the literature on this unique tumor.

Case Reports

Patient 1

A 35-year-old man presented for treatment of a “wart” on the right fifth toe that had increased in size over the last year. He reported that the lesion was mildly painful and occasionally bled or drained clear fluid. He also noted cracking of the nail plate on the same toe. Physical examination revealed a firm, flesh-colored, 3-mm dermal papule on the proximal nail fold of the right fifth toe with subtle flattening of the underlying nail plate (Figure 1). The patient underwent biopsy of the involved proximal nail fold. Histopathology revealed a proliferation of small oval and spindle cells arranged in fascicles and bundles in the dermis (Figure 2). There was extensive mucin deposition associated with the spindle cell proliferation. Additionally, spindle cells and mucin surrounded and entrapped collagen bundles on the periphery of the lesion. Lesional cells were diffusely positive for CD34 and extended to the deep surgical margin (Figure 3). S-100 and factor XIIIa stains were negative. The diagnosis of SAFM was made based on the acral location, histopathologic appearance, and immunohistochemical profile of the tumor.

Figure 1. Firm dermal papule on the proximal nail fold of the right fifth toe with associated nail plate dystrophy. Figure 2. Small oval and spindle cells arranged in fascicles and bundles in the dermis, with extensive mucin deposition and collagen trapping (H&E, original magnification ×100). Figure 3. Tumor cells were positive on CD34 staining (original magnification ×40). Figure 4. Dermal stellate spindle cells arranged in a loose fascicular pattern with marked mucin deposition (H&E, original magnification ×400).

Patient 2

A 47-year-old man presented with an asymptomatic growth on the left fourth toe that had increased in size over the last year. Physical examination revealed an 8-mm, firm, fleshy, flesh-colored, smooth and slightly pedunculated papule on the distal aspect of the left fourth toe. The nail plate and periungual region were not involved. A shave biopsy of the papule was obtained. Histopathology demonstrated dermal stellate spindle cells arranged in a loose fascicular pattern with marked mucin deposition throughout the dermis (Figure 4). Lesional cells were positive for CD34. An S-100 stain highlighted dermal dendritic cells, but lesional cells were negative. No further excision was undertaken, and there was no evidence of recurrence at 1-year follow-up. The diagnosis of SAFM was made based on the acral location, histopathologic appearance, and immunohistochemical profile of the tumor.

Patient 3

A 45-year-old woman presented with asymptomatic distal onycholysis of the right thumbnail of 1 year’s duration. She denied any history of trauma, and no bleeding or pigmentary changes were noted. Physical examination revealed a 5-mm flesh-colored papule on the hyponychium of the right thumb with focal onycholysis (Figure 5). A wedge biopsy of the lesion was performed. Histopathology showed an intradermal nodular proliferation of bland spindle cells arranged in loose fascicles and bundles and embedded in a myxoid stroma (Figure 6). CD34 staining strongly highlighted lesional cells. S-100 and neurofilament stains were negative. The diagnosis of SAFM was made based on the acral location, histopathologic appearance, and immunohistochemical profile of the tumor.

Comment

Clinically, SAFM typically presents as a slow-growing solitary nodule on the distal fingers or toes. The great toe is the most commonly affected digit, and the tumor may be subungual in up to two-thirds of cases.¹ Unusual locations, such as the heel, also have been reported.² Onset typically occurs in the fifth or sixth decade, and there is an approximately 2-fold higher incidence in men than women.^1-3

Histopathologically, SAFM is a characteristically well-circumscribed but unencapsulated dermal tumor composed of spindle and stellate cells in a loose storiform or fascicular arrangement embedded in a myxoid, myxocollagenous, or collagenous stroma.⁴ The tumor often occupies the entire dermis and may extend into the subcutis or occasionally the underlying fascia and bone.^4,5 Mast cells often are prominent, and microvascular accentuation also may be seen. Inflammatory infiltrates and multinucleated giant cells typically are not seen.⁶ Although 2 cases of atypical SAFM have been described,² cellular atypia is not a characteristic feature of SAFM.

The immunohistochemical profile of SAFM is characterized by diffuse or focal expression of CD34, focal expression of epithelial membrane antigen (EMA), CD99 expression, and varying numbers of factor XIIIa–positive histiocytes.^2,3 Positive staining for vimentin also is common. Staining typically is negative for S-100, human melanoma black 45, keratin, smooth muscle actin, and desmin.