Skeletal muscle mass in acromegaly assessed by magnetic resonance imaging and dual-photon x-ray absorptiometry

Abstract

Context: GH and IGF-I are nitrogen retaining and anabolic, but the impact of long-term exposure to supraphysiological GH and IGF-I, either from endogenous overproduction in acromegaly or exogenous sources, on skeletal muscle (SM) mass is not clear.

Objectives: The objectives of the study were to assess SM mass by whole-body magnetic resonance imaging (MRI) in acromegaly and test the hypothesis that dual-energy x-ray absorptiometry (DXA) lean tissue mass-derived estimates of SM accurately estimate true SM mass.

Design, setting, and patients: The design was a cross-sectional study in 27 acromegaly patients compared with predicted models developed in 315 nonacromegaly subjects and to matched controls.

Outcome measures: Mass of SM from whole-body MRI and lean tissue from DXA were measured.

Results: SM mass did not differ from predicted or control values in active acromegaly: 31.75 +/- 8.6 kg (acromegaly) vs. 33.06 +/- 8.9 kg (predicted); SM was 95.6 +/- 12.8% of predicted (range 66.7-122%) (P = 0.088). Lean tissue mass (DXA) was higher in acromegaly than controls: 65.91 +/- 15.2 vs. 58.73 +/- 13.5 kg (P < 0.0001). The difference between lean tissue mass (DXA) and SM in acromegaly patients was higher than that in controls (P < 0.0001) consistent with an enlarged non-SM lean compartment in acromegaly. SM mass predicted by DXA correlated highly with SM mass by MRI (r = 0.97, P < 0.0001). SM (MRI) to SM (DXA predicted) ratio was 1.018 (range 0.896-1.159), indicating high agreement of these measures of SM.

Conclusions: SM mass in active acromegaly patients did not differ from predicted values. SM mass estimated from DXA agreed highly with SM by MRI, supporting the validity of the DXA model in assessing SM in acromegaly and other disorders of GH/IGF-I secretion.

Figures

Figure 1

MRI: ATFM, Adipose tissue-free mass. DXA: BMC, Bone mineral content; lean, total body lean tissue; ALT (includes SM and other soft tissues in arms and legs only). Other tissues include soft tissues and residuals. Adapted from Wang et al. Hydration of fat-free body mass: new physiological modeling approach. Am J Physiol 1999;27:6.

Figure 2

Measured and predicted SM mass in patients with acromegaly. There were no significant between-group differences between measured and predicted SM mass.

Figure 3

ALT by DXA correlated highly with SM by MRI (r = 0.958, P < 0.001).

Figure 4

Bland-Altman plot of the relationship between SM measured by MRI and SM estimated by DXA in patients with acromegaly. The correlation coefficient of the mean of measured SM (MRI) and predicted SM mass (DXA) with the difference between them was r = 0.049 (P = 0.81), demonstrating good agreement.