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Case Reports

Abstract

Background: Fibromyxoid spindle cell neoplasms of the skin present diagnostic challenges, particularly when focal cytologic atypia is present.

Case: A 42-year-old female presented for evaluation of a pruritic growth on the left posterior forearm. This had been previously biopsied approximately two years prior for the same concern, which had demonstrated focal mucinosis. Upon repeat biopsy, the specimen demonstrated fibromyxoid spindle cell neoplasm with focal atypia, lymphohistiocytic inflammatory infiltrate, and scattered giant cells. Immunohistochemistry (IHC) was negative for AE1/AE3, Melan-A, p40, desmin, MUC4, smooth muscle actin (SMA). The S100 staining was positive for scant dermal dendritic cells. The CD34 had focal stromal positivity. The final diagnosis was fibromyxoid spindled cell neoplasm with focal atypia, for which a low-grade fibromyxoid sarcoma (LGFMS) could not be ruled out. The patient was referred for surgical treatment.

Discussion: The differential diagnosis for an atypical fibromyxoid spindled cell neoplasm includes LGFMS, myxoid solitary fibrous tumor (SFT), superficial angiomyxoma, and other rare myxoid spindle cell tumors. The patient's history of focal mucinosis in the same region raises the possibility of a recurrent process, but the presence of focal atypia and giant cells necessitates exclusion of a low-grade sarcoma.

Conclusion: This case underscores the diagnostic challenge posed by fibromyxoid spindle cell neoplasms with atypical features and non-specific IHC. as malignancy cannot be entirely excluded. To our knowledge, recurrence of focal mucinosis with atypia has not been reported. Complete excision is warranted, given the potential for local recurrence and rare risk of late metastasis in some low-grade sarcomas.