Multifocal pseudomyogenic hemangioendothelioma of soft tissue presenting as a painful skin papule: A case report.

Summary: Pseudomyogenic hemangioendothelioma (PMH) is a rare, intermediate soft tissue tumor that primarily affects the extremities. It is characterized by atypical epithelioid and spindled cell proliferation with vascular differentiation, often mimicking high-grade sarcomas. While PMH is typically slow-growing and prone to local recurrence, it rarely metastasizes. Here, we present a case of multifocal PMH in a 43-year-old female with a 9-month history of a painful skin lesion on her posterior thigh, unresponsive to antibiotics. Clinical examination revealed a 1 cm firm, tender pink papule. A shave biopsy demonstrated dermal proliferation of atypical histiocytoid, epithelioid, and spindled cells with eosinophilic cytoplasm and no clear vascular differentiation. Immunohistochemistry confirmed PMH, showing positivity for cytokeratins, ERG, and FosB. INI1 was retained, and desmin was negative, arguing against epithelioid sarcoma and rhabdomyosarcoma. The patient also reported diffuse leg pain, and MRI of the lower extremity revealed multiple homogeneously enhancing intramuscular nodules in the left vastus lateralis, measuring up to 2.9 cm. Further excision of these lesions confirmed multifocal PMH. This case underscores the importance of considering PMH in the differential diagnosis of painful skin lesions and highlights the utility of imaging studies for accurate diagnosis and treatment guidance.