Distal appendicular skeletal involvement of diffuse large B-cell lymphoma on technetium-99m methylenediphosphonate bone scintigraphy and ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography: a case report

A 73-year-old Asian man who had gingival swelling of the labial area of the left maxillary lateral incisor presented to our institution. Initially, it was suspected of being a radicular cyst in the left maxillary sinus incisor. No other symptoms, including fever, cough, or dyspnea, were present. The patient had no family history of cancer. Laboratory data, including tumor markers and peripheral blood appearance, were all within the normal limits. The patient underwent excision of the swelling. A pathological examination revealed a highly pleomorphic large-cell proliferation. Immunohistochemistry was diffusely positive for cluster of differentiation (CD) 20 and B-cell lymphoma 6 proteins. The patient’s Ki-67 index was approximately 80%. His tumor cells were negative for CD3, CD10, and creatine kinase. We diagnosed the tumor as DLBL with an immunohistological staining pattern consistent with germinal center B-cell derivation. PET/CT was performed to determine the stage. Increased FDG uptake in multiple masses and nodular lesions was evident, with maximum standardized uptake values of 12.15 in the left testis, 1.92 in the skin of the right chest, and 2.88 in the left ulna and the third metatarsal bone (Fig. 1a and b). A bone scan performed to diagnose the bone lesions revealed multiple uptakes in the left ulna, hand, both tibiae, and the left foot (Fig. 2a). On the basis of the PET/CT result, left orchiectomy was performed for accurate histological diagnosis. The lesion was confirmed as DLBL. Axial and sagittal T2-weighted magnetic resonance imaging (MRI) showed enhanced signaling of lesions with soft tissue edema in the olecranon of the left ulna (Fig. 3a), the third metacarpal bone of the left hand (Fig. 3b), and the third metatarsal bone of the left foot (Fig. 3c). MRI findings prompted a diagnosis of lymphoma. Eight cycles chemotherapy were given according to the rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone protocol plus external radiotherapy targeted to the involved bone sites for 5 months. Follow-up PET/CT (Fig. 1c) and bone scan (Fig. 2b) revealed the disappearance of hypermetabolism and decreased uptake in lesions compared with the previous images. Laboratory data were also all within the normal limits after chemotherapy.