Incidental Detection of Acute Lymphoblastic Leukemia on [18F]Fluorodeoxyglucose Positron Emission Tomography

Abstract

A 32-year-old woman was referred to our hospital because of diffuse bone pain and a high fever lasting 2 weeks. She had a normal physical examination with no sign of hepatosplenomegaly or adenopathy. The hematological examination revealed no abnormalities; the WBC count was 7,410.0/mm (neutrophils, 84.9%; eosinophils, 0.8%; basophils, 0.4%; monocytes, 1.8%; lymphocytes, 12.2%), hemoglobin was 12.1 g/dL, and platelet count was 221,000/mm. Laboratory tests showed an increased lactate dehydrogenase (409 IU/L; reference range, 120 to 240 IU/L) and C-reactive protein (22.10 mg/dL; reference range, 0.00 to 0.30 mg/dL). Computed tomography (CT) and magnetic resonance imaging found no evidence of abnormalities, while positron emission tomography (PET)/CT with [F]fluorodeoxyglucose (FDG) showed diffuse increased bone marrow uptake (Fig 1). Based on the PET/CT result, we examined a bone marrow aspirate, which revealed 98% lymphoblasts (Fig 2). The leukemic cells in the bone marrow expressed CD19, CD10, CD34, and CD13 antigens. A multiplex real-time quantitative polymerase chain reaction assay showed that the copy number of minor BCR/ABL transcripts was elevated at 1.7 10 copies. She was diagnosed with acute lymphoblastic leukemia with the Philadelphia chromosome, was treated immediately with chemotherapy including imatinib, and achieved molecular complete remission. Routinely, PET/CT is used to find a wide variety of tumors with detection sensitivities and specificities usually exceeding 90%, particularly in cancers of the lung, colon, head and neck, and melanoma. In hematological malignancies, its value for diagnosis and response assessment has been confirmed in lymphoma, myeloid sarcoma, and multiple myeloma. Previous report assessed the response of acute myeloblastic leukemia using PET/CT with [F]fluorodeoxythymidine, although the diagnostic value of PET/CT has not been evaluated thoroughly in leukemia. In several published case reports, PET detected focal bone localization of leukemia, while bone marrow aspiration detected no abnormalities. In our case, leukemic cells were localized in the bone marrow only, while hematological examination of the peripheral blood revealed no abnormalities. PET/CT might be useful for detecting leukemia in cases that are difficult to diagnose, allowing treatment initiation without delay.