Psoas and pectoralis muscle indices and brown adipose tissue activity may be prognostic indicators in older patients with multiple myeloma.

Changes in body composition, particularly sarcopenia and adipose tissue remodeling, have prognostic implications in multiple myeloma (MM). This retrospective study evaluated the prognostic value of PET/CT-derived muscle indices and brown adipose tissue (BAT) activity in 75 MM patients aged ≥ 60 years treated between January 2023 and March 2025. Autologous stem cell transplantation (ASCT) was performed in 41.3% of patients. Median progression-free survival was 6.06 months, with a median follow-up of 25.70 months. ASCT was independently associated with improved overall survival (OR: 0.249, p = 0.060) and a reduced risk of final disease progression (OR: 0.260, p = 0.019). Higher Charlson Comorbidity Index scores independently predicted increased mortality (OR: 1.677, p = 0.017). Reduced skeletal muscle mass, particularly a lower pectoralis major index, was independently associated with disease progression (OR: 0.003, p = 0.012). Among ASCT recipients, higher BAT activity (SUVmean) showed a strong negative correlation with post-transplant progression-free survival (rho = -0.717, p < 0.05). PET/CT-based body composition analysis may provide additional prognostic value in MM.