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

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.

Physical impairment in patients with idiopathic inflammatory myopathies is associated with the American College of Rheumatology functional status measure.

The goals of this study were to assess the predictive value of chart-abstracted American College of Rheumatology functional status (ACR-FS) with patient-reported ACR-FS and to relate it with measures of muscle function in a single-institution cohort of patients with idiopathic inflammatory myopathies (IIMs). Demographic and clinical data of 102 patients with IIMs regularly followed in the Rheumatology and Neurology Clinics at the University of Kentucky Medical Center between 2006 and 2012 were obtained through retrospective chart review. Clinical and functional status evaluation, muscle performance testing, and body composition measures were performed on a subset of 21 patients. ACR-FS was obtained by both chart abstraction and direct patient report. Spearman's correlations were used to examine the relationship of ACR-FS derived from chart abstraction with direct patient report, as well as the relationship of measures of physical function and body composition with ACR-FS. ACR-FS derived from chart abstraction was significantly correlated with ACR-FS derived from direct patient report (ρ = 0.78, p < 0.001). ACR-FS derived from chart abstraction was also significantly correlated with patient-reported physical function (ρ = -0.71, p < 0.001) and physical activity (ρ = -0.58, p < 0.05), manual muscle testing (ρ = -0.66, p < 0.01), and skeletal muscle endurance as measured by the functional index-2 test (shoulder flexion ρ = -0.62, p < 0.01; hip flexion ρ = -0.65, p < 0.0; heel lift ρ = -0.67, p < 0.01; and toe lift ρ = -0.68, p < 0.01). The ACR-FS is a simple measure of disability that can be used in chart abstraction studies involving IIM patients. We have demonstrated that ACR-FS correlates well with muscle performance tests of strength and endurance.