Case Report: Benign myoepithelioma presenting as fever of unknown origin: a rare clinical manifestation of an uncommon tumor.

The etiology of fever of unknown origin (FUO) is complex and diverse, with benign neoplasms remaining a rarely reported cause. This case report describes a young female patient who presented with FUO and persistently elevated inflammatory markers. A comprehensive diagnostic workup revealed no clear evidence of infectious, autoimmune, or malignant disease. However, during hospitalization, a previously stable, painless mass on her left foot, which presented for two years, exhibited increased local skin temperature. Imaging studies identified a metabolically active subcutaneous lesion at the site. The patient's condition improved rapidly following excision of the mass, and histopathological examination confirmed the diagnosis of soft tissue myoepithelioma. Soft tissue myoepithelioma, a rare neoplasm of uncertain differentiation, was identified as the underlying etiology of the patient's clinical presentation. Typically characterized by an indolent and subtle clinical course, this neoplasm most commonly manifests as a painless mass in the extremities or trunk. The disease exhibits a roughly equal sex distribution, with a peak incidence occurring between the ages of 30 and 40 years. Histologically, soft tissue myoepithelioma demonstrates a heterogeneous composition of myoepithelial cell types, predominantly epithelioid cells, and exhibits immunohistochemical expression of both epithelial and myogenic lineage markers. It is noteworthy that fever associated with myoepithelioma is extremely rare, with very few cases reported in the literature to date. This case highlights the rare presentation of soft tissue myoepithelioma as a hyperinflammatory fever, thereby expanding the recognized clinical spectrum of this tumor and deepening the understanding of this distinct entity.