Background: Intramuscular manifestations of malignant immunoproliferative diseases (IMMID) are very rare.
Purpose: To determine the prevalence and the clinical features of IMMID in a large series of patients, and to analyze their radiological appearances.
Material and methods: Between 1997 and 2007, 20 patients with IMMID (non-Hodgkin lymphoma [NHL], n=14, and myeloma, n=6) were identified. All patients underwent computed tomography (CT). In five cases, magnetic resonance imaging (MRI) was additionally performed.
Results: Clinically, 16 patients presented with local pain and soft-tissue swelling. In four patients, IMMID was found incidentally. The most common site was the erector spinae muscle, followed by the iliopsoas and pelvic muscles. In 13 cases of IMMID, diffuse mass-forming muscle infiltration was found. Focal intramuscular masses were identified in seven cases.
Conclusion: NHL mostly manifests as diffuse muscle enlargement, whereas myelomas form focal intramuscular masses. Nevertheless, CT and MR appearances are nonspecific and can be misinterpreted as muscle sarcoma or inflammatory disease. Although rare, muscle involvement should be considered in the differential diagnosis of muscle disorders in patients with non-Hodgkin lymphoma and myeloma.