Diseases showing diffuse bone uptake on FDG-PET

Introduction: In FDG-PET imaging, it is necessary to localize the lesion and differentiate FDG uptake due to malignancy or inflammation from physiological or reactive FDG uptake with little pathological significance. In particular, in the diagnosis of bone marrow lesions in the spine, the differential diagnosis must include degeneration, fracture, reactive uptake in response to increased bone marrow hematopoietic function, bone metastasis, myeloproliferative diseases such as lymphoma, changes secondary to treatment, and recurrence. Bone marrow is a hematopoietic tissue with a physiologically high proliferative capacity. Usually, physiological FDG uptake is relatively low, and FDG uptake increases in cells with increased proliferative capacity. The increased FDG uptake is considered to adequately reflect an increased proliferative capacity of bone marrow cells. Therefore, an increase in white blood cells due to inflammation leads to an increased FDG uptake. However, increased FDG uptake in bone marrow also occurs due to inflammation associated with malignancy and administration of granulocyte-colony stimulating factor and during the recovery from chemotherapy-associated leukopenia. In addition, patients with long-standing severe anemia may also present with increased FDG uptake in bone marrow. The reactive FDG uptake in bone marrow is characterized by diffuse increased uptake in the area where normal hematopoietic bone marrow is distributed. However, diffuse increased uptake in bone is caused not only by a reactive increase in bone marrow hematopoietic function but also by bone metastasis of malignant tumors, malignant lymphoma, and myeloproliferative diseases such as leukemia. In addition, diffuse FDG uptake is seen in cases of myeloproliferative diseases, but it may not be uniform. Here, we present educational cases in which the differential diagnosis for diffuse or multiple increased FDG uptake in bone and bone marrow is required.