Neglected extra-articular manifestations in rheumatoid arthritis patients with normal body mass index: reduced skeletal muscle overlapping overfat

Abstract

Background: Chronic inflammation in rheumatoid arthritis (RA) can induce reduced muscle mass (myopenia) and ectopic fat deposition probably showing normal body mass index (BMI). We aimed to investigate their body composition (BC) characteristics and clinical significance.

Methods: BMI and BC were collected in consecutive RA patients and control subjects. Myopenia was defined by appendicular skeletal muscle mass index (ASMI) ⩽7.0 kg/m² in men and ⩽5.7 kg/m² in women. Overfat was defined by body fat percentage (BF%) as ⩾25% for men and ⩾35% for women.

Results: There were 620 RA patients (57.6% with normal BMI) and 2537 control subjects (62.5% with normal BMI) recruited. After 1:1 age and sex matching with control subjects, RA patients with normal BMI (n = 240) showed significantly higher prevalence of myopenia (43.3% versus 22.1%) and overfat (19.2% versus 7.1%) as well as myopenia overlapping overfat (17.1% versus 3.3%). In all RA patients with normal BMI (n = 357), there were 18.2% patients with myopenia overlapping overfat who had the worst radiographic scores and highest rates of previous glucocorticoid treatment and hypertension. Compared with those without, normal BMI RA patients with previous glucocorticoid treatment (24.4% versus 10.3%) or hypertension (27.8% versus 13.6%) had a higher rate of myopenia overlapping overfat. Previous glucocorticoid treatment [odds ratio (OR) = 2.844, 95% confidence interval (CI) 1.441-5.614] and hypertension (OR = 2.452, 95% CI 1.283-4.685) were potential associated factors of myopenia overlapping overfat in RA patients with normal BMI.

Conclusion: Myopenia overlapping overfat is an important extra-articular manifestation which should not be ignored in RA patients with normal BMI, especially with glucocorticoid treatment and hypertension.

Keywords: body composition; body fat; body mass index; hypertension; rheumatoid arthritis; skeletal muscle.

Figure 1.

Flow diagram of matched rheumatoid arthritis (RA) patients and control subjects with normal body mass index (BMI) for statistical analysis.

Figure 2.

Comparisons of body composition (BC) subgroups between matched rheumatoid arthritis (RA) patients and control subjects with normal body mass index. All, N = 240; female, n = 208; male, n = 32.

Figure 3.

Comparisons of body composition (BC) subgroups between normal body mass index rheumatoid arthritis patients with and without previous glucocorticoid treatment or hypertension. Without previous glucocorticoid treatment, n = 156; with previous glucocorticoid treatment, n = 201; without hypertension, n = 314; with hypertension, n = 43.

Figure 4.

Logistic regression analysis for potential associated factors of myopenia overlapping overfat in rheumatoid arthritis patients with normal body mass index. 28SJC, 28-swollen joint count; 28TJC, 28-joint tender count; ACPA, anti-cyclic citrullinated peptide antibody; CDAI, clinical disease activity index; CI, confidence interval; CRP, C-reactive protein; CVD, cardiovascular disease; DAS28-CRP, disease activity score in 28 joints with four variables including CRP; ESR, erythrocyte sedimentation rate; HAQ-DI, Stanford Health Assessment Questionnaire disability index; JE, joint erosion; JSN, joint space narrowing; mTSS, modified total Sharp score; OR, odds ratio in logistic regression; Pain VAS, pain visual analogue scale; PrGA, provider global assessment of disease activity; PtGA, patient global assessment of disease activity; RF, rheumatoid factor; SDAI, simplified disease activity index.