Does computed tomography-based muscle density predict muscle function and health-related quality of life in patients with idiopathic inflammatory myopathies?

Abstract

Objective: To investigate the association of low-density (lipid-rich) muscle measured by computed tomography (CT) with skeletal muscle function and health-related quality of life in idiopathic inflammatory myopathies (IIMs).

Methods: Seventeen patients and 10 healthy controls underwent CT of the midthigh to quantify high- (30-100 HU) and low-density (0-29 HU) skeletal muscle areas. Anthropometric measures, body composition, physical activity level, health-related quality of life, skeletal muscle strength, endurance, and fatigue were assessed. Patients were compared against controls. The relationship of anthropometric, body composition, and disease variables with measures of muscle function were examined using Spearman's test on the patient group. Linear regression was used to assess the age- and disease-adjusted relationship of muscle quality to physical function and muscle strength.

Results: Patients had higher body fat percentage (P = 0.042), trunk fat mass (P = 0.042), android:gynoid fat (P = 0.033), and midthigh low-density muscle/total muscle area (P < 0.001) compared to controls. Midthigh low-density muscle/total muscle area was negatively correlated with self-reported physical function, strength, and endurance (the Short Form 36 [SF-36] health survey physical functioning [P = 0.004], manual muscle testing [P = 0.020], knee maximal voluntary isometric contraction/thigh mineral-free lean mass [P < 0.001], and the endurance step test [P < 0.001]), suggesting that muscle quality impacts function in IIM. Using multiple linear regression adjusted for age, global disease damage, and total fat mass, poor muscle quality as measured by midthigh low-density muscle/total muscle area was negatively associated with SF-36 physical functioning (P = 0.009).

Conclusion: Midthigh low-density muscle/total muscle area is a good predictor of muscle strength, endurance, and health-related quality of life as it pertains to physical functioning in patients with IIMs.

© 2015, American College of Rheumatology.

Figures

Figure 1

Differences in low density muscle content are depicted in the CT images of the mid-thigh as variations in gray contrasting color. A, 32-year-old healthy control, in whom the mid-thigh low density muscle area and low density muscle/ high density muscle measured 19.68 cm2 and 0.10, respectively. B, 64-year-old patient with sIBM, in whom the mid-thigh low density muscle area and low density muscle/ high density muscle measured 46.67 cm2 and 0.59, respectively.