Track: Case Reports

Abstract:

Fibro-osseous pseudotumor of the digit (FOPD) is a rare, benign tumor that most commonly affects the soft tissues of the extremities, particularly the hands, and often develops following trauma. The classic clinical presentation is of a progressive painless exophytic mass, occasionally markedly expanding, prompting histopathologic analysis to rule out infection or malignancy. Histologically, they possess a characteristic zonal pattern with a core of fibro/myofibroblastic proliferation and rich vasculature, and peripheral osteoid calcification with mature bone formation. A USP6 gene rearrangement has been identified in many reported cases, though its absence does not exclude the diagnosis. We report a case of a 52-year-old male presenting with a painless, friable, pink subungual nodule on the right hallux, displacing the nail plate and associated with recurrent superimposed infection, inflammation, and drainage. Due to the clinical appearance, differential considerations included pyogenic granuloma, glomus tumor, amelanotic melanoma or other skin cancer, onychopapilloma, onychomatricoma, myositis ossificans, and subungual exostosis. Histologic evaluation revealed an ulcerated subcuticular mass composed of hypercellular fascicles of uniform spindle cells and interspersed woven bone without a cartilaginous cap. No USP6 gene rearrangement was found, distinguishing this case from most previously reported lesions. Furthermore, this case involved the toe, unlike most reported cases involving the finger. We discuss the diagnostic approach and review distinguishing clinical and histologic features from other subungual entities, including subungual exostosis, giant cell tumor, and extra-skeletal osteosarcoma. This case expands on the clinicopathologic spectrum of FOPD and underscores the importance of comprehensive histologic and molecular evaluation in atypical presentations.

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Paolo Vignali