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 [r2   = 0.90, standard error of the estimate (SEE) = 0.23 kg, P < 0.0001] and MMMRI-ABS (r2  = 0.82, SEE = 0.28 kg, P < 0.0001). LMDXA-KE predicted MMMRI-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.