A Massive Haemothorax Due to Pleural Extramedullary Haematopoiesis in a Patient With Myelodysplastic Syndrome/Myeloproliferative Neoplasm.

Extramedullary haematopoiesis (EMH) refers to blood cell production outside the bone marrow, typically in reticuloendothelial organs such as spleen, liver, and lymph nodes, as a compensatory response to haematopoietic stress. We describe a rare case of recurrent haemothorax caused by pleural EMH in a female patient in her 60s with myelodysplastic/myeloproliferative neoplasm (MDS/MPN) not otherwise specified (NOS). She had recurrent presentations with transfusion-dependent anaemia, fevers, splenomegaly, and bone marrow morphology consistent with MDS/MPN. Over the course of her disease, she developed recurrent left-sided pleural effusions and haemothorax, initially managed with repeated drainage. Video-assisted thoracoscopic surgery (VATS) with pleural biopsy confirmed EMH with infiltration by myeloid precursors and megakaryocytes. Despite azacitidine therapy and supportive management, her condition progressed to multi-organ failure and death. The case highlights an unusual site of EMH and emphasises the need to consider EMH in the differential diagnosis of haemorrhagic pleural effusions in patients with malignant haematological disorders.