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 (MM_MRI-WM), absolute muscle mass (MM_MRI-ABS) after excluding IMF, and knee extensor muscle mass (MM_MRI-KE). DXA was used to measure thigh LM (LM_DXA) and (FFM_DXA). To predict MM_MRI-KE, LM_DXA was multiplied by 0.52 and yielded LM_DXA-KE.

Results: LM_DXA predicted MM_MRI-WM r²_?=?0.90, standard error of the estimate (SEE)?=?0.23?kg, P?<?0.0001] and MM_MRI-ABS (r²?=?0.82, SEE?=?0.28?kg, P?<?0.0001). LM_DXA-KE predicted MM_MRI-KE (r²?=?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.