Diffuse pulmonary extramedullary hematopoiesis in myelofibrosis diagnosed with technetium‐99m sulfur colloid bone marrow scintigraphy and single photon emission computerized tomography/ <scp>CT</scp>
Authors: Ming Yang, Michael Roarke
Journal: American Journal of Hematology (2016)

A 72-year-old man with advanced myelofibrosis presented acute onset of dyspnea. Physical examination revealed mild elevation of jugular venous pressure. The laboratory results showed pancytopenia. Chest X-ray is unremarkable. Two-dimension (2D) transthoracic echocardiogram demonstrated moderate degree right ventricular enlargement, mild tricuspid valve regurgitation, and elevated right ventricular systolic pressure, consistent with pulmonary hypertension (PTH). Technetium (Tc)−99m sulfur colloid (SC) bone marrow scintigraphy and SPECT/CT scan of chest demonstrated extramedullary hematopoiesis (EMH) in the liver and spleen, as well as diffuse bilateral pulmonary EMH (Figure 1). A lung biopsy was not performed due to hemorrhagic risk. Patient received whole lung palliative radiation therapy to a dose of 100 cGy in a single fraction, followed by significant improvement of dyspnea. Whole body planar images at anterior and posterior projections (A, B). There are decreased radiotracer uptake in the axial and appendicular skeleton, remarkably increased radiotracer uptake in liver and spleen, as well as splenomegaly, compatible with EMH. In addition, there are bilateral lung fields diffuse mild degree increased uptake (arrows). SPECT/CT images of chest (C-F). Low dose CT images show bilateral lung diffuse ground-glass opacity (representative axial and coronal planes, C, E). Fused SPECT and CT images at same plane (D, F) show bilateral lung diffuse increased radiotracer uptake. Findings indicate diffuse pulmonary EMH [Color figure can be viewed at wileyonlinelibrary.com] The EMH is a hematopoietic disorder occurring at reticulo-endothelial system outside the bone marrow compartment, usually seen in the liver and spleen. It is a common complication of multiple hematological diseases, including myelofibrosis, sickle cell anemia, and thalassemia, etc. Within the thorax, EMH has been found in paraspinal region, pleural space, lung, and more rarely, pulmonary artery.1 On chest CT, pulmonary EMH might manifest as atypical diffuse groundglass opacity, pulmonary nodules, and/or interstitial thickening.2 Under microscopy, there is accumulation of monocytes, megakaryocytes, and erythroblasts with associated obliteration of lymphatic flow.3 The microscopic findings are typical for myeloid metaplasia, which is an interchangeable term to describe histopathological process of pulmonary EMH. It is believed that hematopoietic infiltration of the pulmonary parenchyma may account in part for the development of PTH. Dyspnea is a frequent symptom in myelofibrosis, usually caused by hepatosplenomegaly and/or anemia. However, in patients with worsening respiratory symptom. PTH should be considered as a confounding etiology. Non-invasive 2D-echocardiography is the imaging modality to evaluate right heart function. Nuclear medicine Tc-99m SC bone marrow scintigraphy and SPECT/CT play a vital role in the detection of diffuse pulmonary EMH and monitoring therapy response.4, 5 Lung biopsy, the gold standard in diagnosis of pulmonary EMH, is not indicated in most clinical scenarios due to sample error likelihood and high risk of hemorrhage. As hematopoietic tissue is extremely radiosensitive, the palliative whole lung low dose radiation therapy is usually curative of this disorder. Our case has highlighted the unique role of Tc-99m SC bone marrow scintigraphy and SPECT/CT in the diagnosis of diffuse pulmonary EMH. Prompt diagnosis of this rare etiology should initiate whole lung low dose radiation therapy to achieve favorable clinical response without side effects of radiation.