Case of polycythemia vera with unusual organizing pneumonia mimicking the clinical features of military tuberculosis and possibly caused by the involvement of neoplastic megakaryocytes.

Polycythemia vera (PV) is a clonal myeloproliferative neoplasm (MPN) of hematopoietic stem cells. Although the management of MPN patients generally focuses on the prevention of thromboembolic events caused by hypercoagulability, it is true that the patients with hematological malignancy often suffer from pulmonary diseases with atypical radiological patterns. We present here a 56-year-old woman with PV harboring a JAK2(V617F) mutation that had a diffuse reticulonodular pattern on chest radiography and was initially suspected of having military tuberculosis. Pathological assessment of a video-assisted thoracoscopic surgery lung biopsy revealed that the lesions were in fact organizing pneumonia (OP). Interestingly, pulmonary extramedullary hematopoiesis with a diffuse plugging of the alveolar blood capillaries by numerous atypical megakaryocytes was also observed around the granulation components. The histological findings of our case of unusual OP suggest that local activated neoplastic megakaryocytes and platelets played an important role in the development of spreading fibrotic lesions. JAK2 mutation or the preleukemic phase of MPN may accelerate the activation of megakaryocytes and result in the proliferative process of fibrosis.