Pauciarticular onset juvenile idiopathic arthritis (JIA) or pauciarthritis (formerly called pauciarticular onset juvenile rheumatoid arthritis) is the subset of JIA that includes patients with involvement of fewer than five joints. It is the most common subgroup, constituting about 50 percent of cases of JIA (table 1). A proposed nomenclature divides this group into persistent pauciarthritis (no additional joint involvement after the first six months of illness) and extended pauciarthritis (involvement of four or less joints during the first six months of illness; additional joints are involved over time, resulting in more than four joints ultimately being affected). (See "Classification of juvenile arthritis (JRA/JIA)".)
The clinical issues related to pauciarticular onset JIA are discussed in this review. Systemic onset and polyarticular onset JIA are discussed separately. (See "Systemic onset juvenile idiopathic arthritis: Clinical manifestations and diagnosis" and "Polyarticular onset juvenile idiopathic arthritis: Clinical manifestations and diagnosis".)
Pauciarticular onset juvenile idiopathic arthritis (JIA) affects females more often than males, as does polyarticular disease. The peak incidence of pauciarticular onset JIA is in the second and third years. It is less common over 5 years of age and rarely begins after age 10. A child with large joint involvement beginning in the early teenage years most commonly has a spondyloarthropathy. The spondyloarthropathies are called "enthesitis-related arthritis", which is a distinct subset of juvenile idiopathic arthritis (JIA) in the new nomenclature. (See "Spondyloarthropathy in children".)
The typical child with pauciarticular onset JIA is a girl who is noticed to be limping without complaint. Often the family notices that the child "walks funny" in the morning, but after a little while seems fine. In many cases, the child has never complained of pain; the family seeks medical advice only because the knee is swollen. It is unusual for the family to be able to specify exactly when the illness started.
Pauciarticular onset JIA affects the large joints (knees, ankles, wrists, elbows), but virtually never begins in the hips. There are several other types of arthritis that may have pauciarticular onset in this age group, but are not juvenile rheumatoid arthritis (JRA). However, under the new nomenclature these conditions are covered under the classification of pauciarticular JIA. Systemic manifestations (other than uveitis) are characteristically absent. Thus, fever, rash, or other constitutional symptoms suggest a different diagnosis. (See 'Differential diagnosis' below.)