Cutaneous Extramedullary Hematopoiesis in Primary Myelofibrosis: A Case Report With Rapidly Fatal Outcome.

Extramedullary hematopoiesis (EMH) is the formation of hematopoietic cells outside the bone marrow, typically as a compensatory mechanism in the setting of marrow failure. Cutaneous EMH is an exceptionally rare manifestation, usually associated with chronic myeloproliferative disorders such as primary myelofibrosis. We report the case of a 54-year-old woman with Janus kinase 2 (JAK2)-positive primary myelofibrosis and long-standing transfusion-dependent cytopenias who presented with multiple firm, erythematous-to-violaceous nodular lesions on the trunk. Histological examination of a skin biopsy revealed a dermal infiltrate composed of myeloid precursors with diffuse myeloperoxidase expression, consistent with cutaneous EMH. Bone marrow evaluation confirmed advanced myelofibrosis without acute transformation. Despite supportive care, the patient's condition rapidly deteriorated, and she died two weeks after presentation. This case highlights the rarity of cutaneous EMH, its association with advanced marrow failure, and its poor prognostic significance. Recognition of this manifestation may provide insight into the severity of hematopoietic exhaustion and guide clinical management in patients with myeloproliferative disorders.