Prediction of thigh skeletal muscle mass using dual energy x-ray absorptiometry compared to magnetic resonance imaging after spinal cord injury

Objectives: A rapid decline in lean mass (LM), fat-free mass (FFM) and increased intramuscular fat (IMF) predispose persons with spinal cord injury (SCI) to chronic medical conditions including dyslipidemia, insulin resistance, type 2 diabetes mellitus and cardiovascular disease. (1) To determine the relationship between dual energy x ray absorptiometry (DXA) and gold standard magnetic resonance imaging (MRI) LM values; (2) to develop predictive equations based on this relationship for assessing thigh LM in persons with chronic SCI. Study Design: Cross-sectional predicational design. Settings: Clinical research medical center. Participants: Thirty-two men with chronic (> 1 y post-injury) motor complete SCI. Methods: Participants completed total body DXA scans to determine thigh LM and were compared to measurements acquired from trans-axial MRI. Outcome measures: MRI was used to measure whole muscle mass (MMMRI-WM), absolute muscle mass (MMMRI-ABS) after excluding IMF, and knee extensor muscle mass (MMMRI-KE). DXA was used to measure thigh LM (LMDXA) and (FFMDXA). To predict MMMRI-KE, LMDXA was multiplied by 0.52 and yielded LMDXA-KE. Results: LMDXA predicted MMMRI-WM [r(2) = 0.90, standard error of the estimate (SEE) = 0.23kg, P<0.0001] and MMMRI-ABS (r(2) = 0.82, SEE = 0.28kg, P<0.0001). LMDXA-KE predicted MMMRI-KE (r(2) = 0.78, SEE = 0.16 kg, P<0.0001). Conclusion: DXA measurements revealed an acceptable agreement with the gold standard MRI and may be a viable alternative for assessing thigh skeletal muscle mass after SCI.