Bilateral psoas muscle lymphoma: an unusual presentation of EBV-positive diffuse large B-cell lymphoma of the elderly.

Abstract

diffuse large B-cell lymphoma (DLBCL) of the elderly. Systemic/nodal involvement, including bone marrow, was absent. The viral load of the EBV was not measured. Treatment was initiated with R-CHOP (rituximab, cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisone), and lumbago and right femoral pain were gradually relieved. Conversely, serum LDH was elevated before initiating the second course of R-CHOP. Mass lesions were enlarged on enhanced CT. The treatment regimen was changed to EPOCH-R (etoposide, prednisone, vincristine, cyclophosphamide, hydroxydaunorubicin, and rituximab), and has been continuing to the time of this writing. Skeletal muscle lymphoma (SML) is a very rare disorder, which accounts for 0.1–1.4 % of reported extranodal lymphomas [1, 2]. The most common histologic subtype of soft tissue lymphoma including SML is DLBCL, which accounts for more than 50 % [3]. Soft tissue DLBCL appears to be with aggressive features and dismal prognosis, while the best treatment strategy has not been established because of the rarity [3]. SML is prone to occur in the extremities, such as thigh, calf, and upper arm [3, 4]. Lymphoma in the bilateral psoas muscle mass only is quite rare. This case illustrates that psoas muscle lymphoma should be considered as an unusual cause of serious lumbago and enlarged psoas muscle. A 67-year-old Japanese man with no significant medical history experienced lumbago of about 6 months duration and presented with a 2-week history of right femoral pain and paralysis with serious back pain. He could not lie in the dorsal position due to pain, and rested on the right side in the chest–knee position. Laboratory tests showed markedly elevated serum lactate dehydrogenase (LDH, 1108 IU/L) and slightly elevated soluble interleukin-2 receptor (sIL2R, 632 U/mL). A transverse computerized tomography (CT) image showed size asymmetry of the psoas muscles (Fig. 1a). Enhanced CT detected bilateral masses with ring enhancement (Fig. 1b1, b2). T2 weighted magnetic resonance imaging (MRI) revealed a round, 44 × 22 mm, high-intensity mass in the right psoas muscle at the level of L2–4 (Fig. 1c). A CT-guided needle biopsy demonstrated sheets of roundto oval-shaped large lymphoid cells with large prominent nucleoli. Numerous atypical mitotic cells and foci of necrosis were present (Fig. 1d1). In immunohistochemical analysis, the atypical cells were positive for CD79a, CD20 (Fig. 1d2), bcl-2, MUM-1, and CD43 and negative for CD3, CD4, CD5, CD8, CD10, bcl-1, and bcl-6. In situ hybridization for Epstein-Barr virus (EBV) encoded RNA (EBER) revealed many positive cells (Fig. 1d3). On the basis of the morphological and immunophenotypic features, the patient was given the diagnosis of EBV-positive