Musculoskeletal and functional muscle-bone analysis in children with rheumatic disease using peripheral quantitative computed tomography

Bone demineralization is a severe complication of juvenile idiopathic arthritis (JIA) and other rheumatic diseases. To identify patients, who are at risk of bone disease, musculoskeletal analysis is performed. Furthermore, a more functional approach is needed to assess, whether bone strength is adequate for muscle force and whether muscle force is adequate for body size. In patients with a chronic disease it is most important to differentiate between primary bone problems and those that are secondary to low muscle force. To implement this approach, we measured musculoskeletal parameters of the radius in 94 patients with juvenile idiopathic arthritis of different subtypes and connective tissue disease using peripheral quantitative computed tomography. The four groups consisted of patients with oligoarticular (n=31), polyarticular (n=27), systemic JIA (n=20) and connective tissue disease (CTD) (n=16). All patients with systemic JIA and CTD and 56% of the patients with polyarticular JIA were under treatment with glucocorticoids. In general, the longer the duration of the disease and the more severe the subtype of the rheumatic disease, the shorter the height and the lower the bone density and bone strength parameters. Mean height, bone mineral content (BMC) and muscle cross-sectional area (CSA) were low for age, but muscle CSA was normal for height with the exception of patients with polyarticular disease. In the systemic JIA group the ratio of BMC per muscle CSA was decreased by -1.7 +/- 2.7 SD (P < 0.05), suggesting that bone strength was not adequately adapted to muscle force. This was even more expressed in females than in males (14 versus 3). These patients need closer follow up and potential specific therapeutic intervention.