Polyarticular onset juvenile idiopathic arthritis (formerly called polyarticular onset juvenile rheumatoid arthritis) is a subset of juvenile idiopathic arthritis (JIA) that is defined by the presence of more than four affected joints during the first six months of illness . In the new nomenclature, this disease, which comprises 20 to 30 percent of patients with JIA, is included in the group termed childhood polyarthritis. (See "Classification of juvenile arthritis (JRA/JIA)".)
The clinical manifestations and diagnosis of polyarticular onset JIA will be reviewed here. The management of polyarticular onset JIA and systemic onset and pauciarticular onset JIA are discussed separately. (See "Polyarticular onset juvenile idiopathic arthritis: Management" and "Systemic juvenile idiopathic arthritis: Clinical manifestations and diagnosis" and "Pauciarticular onset juvenile idiopathic arthritis".)
Polyarticular onset juvenile idiopathic arthritis (JIA) is more frequent in females than males. There is a bimodal distribution of the age at onset: the first peak is between the ages of two and five years, and the second between 10 and 14 years. This age distribution suggests that two or more distinct diseases may be included in this classification. The clinical presentation of polyarticular onset JIA is varied, although it tends to fall into patterns based upon the age of onset.
Younger children — In children less than 10 years of age, polyarticular onset JIA often begins similarly to pauciarticular disease with one or two joints affected. The disease then spreads to involve five or more joints during the first six months after disease onset. In young children, the development is often indolent, and the disease may be unrecognized until an intercurrent infection precipitates a dramatic increase in symptoms .
It is uncommon for these patients to develop polyarthritis within a period of days or weeks. More often, their disease is relentlessly progressive with periods of apparent response to therapy, followed by relapses with an increasing number of involved joints. A rapid onset of polyarthritis is more characteristic of reactive arthritis in childhood, but some children present with a history of sudden onset due to a failure to recognize the initial symptoms of the arthritis.