Unusual Skeletal Muscle Recurrence of Mantle Cell Lymphoma After Rituximab Maintenance Therapy Detected on 18F-FDG PET/CT

Mantle cell lymphoma (MCL) is a rare and aggressive subtype of non-Hodgkin lymphoma that typically presents with lymphadenopathy and extranodal involvement, most commonly affecting the spleen and gastrointestinal tract. Skeletal muscle infiltration is exceedingly rare, particularly in MCL. We report the case of a 64-year-old woman with MCL who initially achieved complete metabolic remission following R-CHOP chemotherapy and rituximab maintenance. However, restaging with 18F-FDG PET/CT revealed extensive skeletal muscle recurrence. This case underscores the critical role of 18F-FDG PET/CT in identifying atypical relapse patterns in MCL and highlights the need for vigilant, long-term surveillance following therapy.