18F-FDG-PET/CT is effective in distinguishing myelofibrosis due to bone marrow infiltration of diffuse large B-cell lymphoma from triple-negative primary myelofibrosis.

Although myelofibrosis is mainly associated with myeloproliferative neoplasms (MPN), especially primary myelofibrosis (PMF), a variety of hematological malignancies, including acute myeloid leukemia, multiple myeloma and malignant lymphoma, also cause myelofibrosis with markedly varying degrees of severity. Thus, it is extremely important to accurately diagnose the underlying diseases that cause fibrosis in bone marrow. Analyses of JAK2, MPL and calreticulin gene mutations are useful for distinguishing MPN from other diseases, since 90% of MPN patients have a mutation in one of these genes. However, 10% of PMF patients do not have mutations in any of these genes, and these patients have a disease known as triple negative PMF. It is sometimes difficult to accurately distinguish triple negative PMF from secondary myelofibrosis caused by other diseases. Herein, we present a case of diffuse large B cell lymphoma (DLBCL) with bone marrow involvement, mimicking triple negative primary myelofibrosis. 18F-FDG-PET was useful for correctly diagnosing DLBCL.