Patients with severe, long-standing juvenile idiopathic arthritis have significant deficits in trabecular bone mineral density and cortical bone strength, according to findings published in the August issue of Arthritis and Rheumatism.
"Juvenile idiopathic arthritis (JIA) is the most common pediatric rheumatic disease," Dr. Jon M. Burnham of Children's Hospital of Philadelphia, Pennsylvania, and colleagues write. "The impact of childhood arthritis on bone health may be immediate, resulting in childhood fractures, or it may be delayed, resulting from suboptimal peak bone mass attainment or persistent disease activity."
The researchers performed peripheral quantitative computed tomography of the tibia to assess muscle and bone deficits in 101 children and adolescents with JIA with a spectrum of disease activity as compared with 830 healthy controls.
Of the 101 patients with JIA, 24 had oligoarticular JIA, 40 had polyarticular JIA, 18 had systemic JIA, and 19 had spondylarthritis. The median duration of JIA was 40 months. Overall, 29 per cent of JIA patients had active arthritis, and 28 per cent had received glucocorticoid therapy during the previous 12 months.
The muscle cross-sectional area (mCSA) and section modulus Z scores were significantly lower in patients with polyarticular JIA and spondylarthritis compared to controls subjects. Patients with polyarticular JIA, systemic JIA, and spondylarthritis had significantly lower trabecular volumetric bone mineral density Z scores.
"Cortical bone strength was low because the outer dimension of the tibia, the periosteal circumference, was smaller than controls, which indicated that the bones were thin," Dr. Burnham explained to Reuters Health.
Significant predictors of musculoskeletal deficits included active arthritis in the previous six months, temporomandibular joint disease, functional disability, short stature, infliximab exposure, and JIA duration. After adjustment for age and limb length, the section modulus in JIA patients was significantly reduced relative to mCSA.
"The majority of patients were in clinical remission, given the recent advances in JIA therapy, including TNF-alpha inhibition," Dr. Burnham noted. "However, marked bone deficits persisted, particularly among those with polyarticular JIA and spondylarthropathies and in association with low muscle mass," he said.
"In addition, we determined that JIA is likely a mixed bone disorder - that there is a primary bone effect of JIA in combination with a deficit secondary to low muscle mass," Dr. Burnham said.
Along with previous findings, the current study results suggest that "the optimal time for intervention to maximize bone strength is during childhood so that a normal peak bone mass is achieved," he added.
His group is now looking at spine bone health in JIA. "These data, along with the data from the tibia, will paint a full picture of the problem and help determine the best methods to follow bone mass in JIA and the optimal intervention," Dr. Burnham concluded. "We are not certain yet whether the intervention should be pharmacologic or targeted towards increasing muscle mass to induce beneficial changes in bone."
Arthritis Rheum 2008;58:2518-2527
