Muscle function in Juvenile Idiopathic Arthritis : A two-year follow-up

Abstract: This is a study of muscle function in Juvenile Idiopathic Arthritis (JIA). Rheumatoid arthritis (RA) is a disease that primarily affects the synovial membrane of joints. Muscle weakness, atrophy and pain occur in adult RA. This may be a consequence of joint pain, stiffness and immobility. Muscle inflammation and neuropathy occur as complications in adults. Muscle function in JIA has been much less studied.The aim of the study was to examine whether muscle weakness and atrophy also occur in children with JIA.This was a longitudinal study over a two-year period, where muscle strength and thickness were measured repeatedly in a group of 20 children and teenagers with JIA. Muscle strength was measured using different methods and in several muscle groups. Muscle biopsies were obtained and nerve conduction velocity studies performed.The study concludes that, compared to healthy people, children and teenagers with JIA have as a group reduced muscle strength and muscle thickness. For most of these children and teenagers, muscle strength is only slightly lower than expected, but a few have marked muscle weakness. This is most apparent in patients with severe polyarthritis where the weakness seems to be widespread. Patients with isolated arthritis may also have greatly reduced strength and thickness of muscles near the inflamed joint.There is a risk of decreasing strength in patients with polyarthritis and in muscles near an active arthritis.Minor changes are common in muscle biopsies, and findings may indicate immunological activity in the muscles.Atrophy of type II fibres, as in adult RA, was not found in JIA.No patient had signs of neuropathy.