Abstract
To assess muscle function and functional abilities in children with juvenile idiopathic arthritis (JIA). Fourteen children with JIA and 14 healthy controls matched for age and sex were included. Muscle characteristics, both structural (thickness, cross-sectional area (CSA) and fascicle angle) and qualitative (intermuscular adipose tissue; IMAT), were assessed in thigh muscles using ultrasound and peripheral quantitative computed tomography (pQCT). Muscle function and functional abilities were determined from the assessment of maximal voluntary isometric contraction (MVIC) knee extensors force and vertical jump performance. No significant difference in MVIC force was observed between the two groups. However, squat jump height was significantly reduced in children with JIA (18.3±5.4 vs 24.3±7.9cm, P<.05). No differences in structural parameters were observed, but IMAT/CSA (0.22±0.02 vs 0.25±0.03; P=.01) was significantly lower in children with JIA than in healthy children. Knee extensor muscle architecture and force were comparable between children with and without JIA, but functional abilities (vertical jump performance) were poorer in JIA. The lower IMAT area in JIA could result from a lower physical activity level compared with healthy children.
Highlights
In juvenile idiopathic arthritis (JIA) the pain is due to a chronic inflammatory state induced by an overproduction of pro-inflammatory cytokines such as interleukins (IL) 1 and 6, and tumor necrosis factor alpha
Architectural parameters No significant difference for muscle thickness, fascicle angle or thigh cross-sectional area (CSA) was observed between the two groups (Tables 2 and 3)
intermuscular adipose tissue (IMAT) normalized to CSA was significantly lower in children with JIA than in healthy controls (0.22 ± 0.02 vs 0.25 ± 0.03, p = 0.01)
Summary
In juvenile idiopathic arthritis (JIA) the pain is due to a chronic inflammatory state induced by an overproduction of pro-inflammatory cytokines such as interleukins (IL) 1 and 6, and tumor necrosis factor alpha. If previous studies have shown that children with JIA have impaired physical fitness [1] and muscle strength [2] compared to healthy children, recent studies observed no significant difference for cardiorespiratory fitness and muscle strength, regardless of sub-types of JIA or disease activity [3,4], probably associated with improvement of treatment These alterations were mainly characterized by architectural impairments such as decreased muscular thickness (the distance between superior and inferior aponeuroses) [5,6] and fascicle angle (i.e. the angle between the deep aponeurosis and the interspaces among the fascicles) [7]. Few data are available in the literature regarding the effect of JIA on architectural impairments
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