Presentation
Longstanding swelling right thigh with weight loss. No preceding history of malignancy or trauma.
Patient Data
Soft tissue mass, located within the superficial and deep posterior compartments and extending to the lateral leg. The lesion is homogenous, demonstrating T1-weighted isointensity and T2-weighted hyperintensity.
There is no significant perilesional edema, internal calcification, hemorrhage, or joint space involvement. Neurovascular structures are encased but not infiltrated. Muscular involvement includes the adductor longus, adductor magnus, vastus intermedius, vastus medialis, short head of biceps, semitendinosus, semimembranosus, sartorius, and gracilis muscles.
A thin circumferential periosteal reaction with hyperintense signal on the PDFS sequence is noted along the femur, with overlying skin thickening on the medial aspect. The remaining imaged areas, including the abdomen, pelvis, and left limb, appear unremarkable.
Nuclear medicine study shows FDG uptake in the right thigh, consistent with muscle lymphoma ( biopsy-confirmed) and demonstrate interval improvement and treatment response compared with preceding MRI. There is an incidental left retrosternal lymph node, which may represent either reactive changes or additional involvement. The study aids in assessing treatment effectiveness and monitoring disease progression or remission.
PCR-based analysis of immunoglobulin heavy chain (IgH) gene rearrangements is widely used for diagnosing B-cell lymphomas but has a sensitivity of less than 80%, particularly in germinal center (GC) and post-GC B-cell lymphomas. To improve detection, PCR strategies targeting immunoglobulin light chain (IgL) genes (Igκ and Igλ). In the literature, B-cell clonality detection rates were 74% for IgH, 56.5% for Igκ, and 43.5% for Igλ, increasing to 93.5% when combined. Polyclonal patterns were observed in reactive tissues, highlighting that IgL analysis complements IgH methods, achieving high clonality detection even with poorly preserved DNA in routine histological specimens4.
Case Discussion
Skeletal muscle lymphoma is a rare form of diffuse large B cell lymphoma (DLBCL), most frequently affecting the thigh, upper extremities, calf, and pelvis 1.
MRI features include enlargement of muscular structures, with preservation of the architecture of the tissue and surrounding anatomical structures 2. Definitive diagnosis relies on histological and immunohistological analysis of a sample obtained through imaging-guided biopsy 3, which has confirmed the diagnosis in this case.
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