Soft tissue body composition differences in monozygotic twins discordant for spinal cord injury

To determine the effect of paralysis on body composition, eight pairs of ma le monozygotic twins, one twin in each pair with paraplegia, were studied b y dual-energy X-ray absorptiometry. Significant loss of total body lean tis sue mass was found in the paralyzed twins compared with their able-bodied c o-twins: 47.5 +/- 6.7 vs. 60.1 +/- 7.8 (SD) kg (P < 0.005). Regionally, arm lean tissue mass was not different between the twin pairs, whereas trunk a nd leg lean tissue masses were significantly lower in the paralyzed twins: -3.0 +/- 3.3 kg (P < 0.05) and -10.1 +/- 4.0 kg (P < 0.0005), respectively. Bone mineral content of the total body and legs was significantly related to lean tissue mass in the able-bodied twins (R = 0.88 and 0.98, respective ly) but not in the paralyzed twins. However, the intrapair difference score s for bone and lean tissue mass mere significantly related (R = 0.80 and 0. 81, respectively). The paralyzed twins had significantly more total body fa t mass and percent fat per unit body mass index than the able-bodied twins: 4.8 kg (P < 0.05) and 7 +/- 2% (P < 0.01). In the paralyzed twins, total b ody lean tissue was significantly lost (mostly from the trunk and legs), in dependent of age, at a rate of 3.9 +/- 0.2 kg per 5-yr period of paralysis (R = 0.87, P < 0.005). Extreme disuse from paralysis appears to contribute to a parallel loss of bone with loss of lean tissue in the legs. The contin uous lean tissue lass may represent a form of sarcopenia that is progressiv e and accelerated compared with that in ambulatory individuals.