[Hidden IgM rheumatoid factor in chronic juvenile arthritis. An open multicenter diagnostic study].

244 patients with a provisional diagnosis of juvenile chronic arthritis were investigated for serological presence of "hidden" IgM-rheumatoid-factor with a newly developed ELISA-technique. By clinical and laboratory criteria 130 patients were left with proven JCA. In active polyarticular disease "hidden" IgM-RF was found in 65%, whereas in pauciarticular disease (type I, II) a positive "hidden" IgM-RF rather excludes a patient from these two groups. A positive "hidden" IgM-RF with pauciarticular onset was seen in older girls (greater than 10 years) even in an inactive state and in younger patients with a changing clinical pattern to polyarticular disease.