CLINICAL FEATURES OF JIA SUBTYPES
Systemic-onset JIA presents with many extra-articular features and represents 10% to 20% of all JIA (92). Diagnosis requires arthritis in more than one joint for at least 6 weeks' duration in a child aged below 16 years accompanied or preceded by quotidian fever (spikes >39 degree Celsius once a day with return to normal between peaks) of 3 days' duration, plus one or more of the following: evanescent salmon-colored rash, generalized lymphade-nopathy, hepatomegaly, splenomegaly, or serositis (91,94).
The goal of treatment for systemic JIA is similar to other categories of JIA, and focuses on the prompt control of active inflammation and symptoms, and the prevention of disease- and/or treatment- related morbidities such as growth disturbances, joint damage, and functional limitations (106). About 5% to 8% of children with systemic JIA develop a life-threatening complication known as Macrophage Activation Syndrome (107) with persistent fever, lymphadenopathy, and splenomegaly, and there is profound depression in one or more of the blood cell lines (often initially platelets) with raised liver function enzymes and clotting abnormalities. Definitive bone marrow examination shows numerous well-differentiated macrophages actively phagocytizing hematopoietic elements (108).
In one-half of children with systemic JIA, the course follows a relapsing-remitting course, with arthritis accompanying febrile episodes, then remission once systemic features are controlled. Long-term outlook for these children is usually good. In the other half, the disease is unremitting, with resultant severe joint destruction, and is probably the most severe JIA subtype (89,109). Poor prognostic signs include the continued presence of systemic features and a platelet count exceeding 600,000/mm3, 6 months after onset (95). At least one-third of children will develop severe arthritis (110).
Oligoarthritis is classified into two subtypes: persistent (affecting not more than four joints throughout the disease course) and extended (affecting more than four joints after the first 6 months of disease). Characteristically, there is an early onset before 6 years of age of an asymmetric arthritis, usually in the lower limbs, and predominantly in females. Antinuclear antibodies (ANAs) are detected in substantial titers in about 70% to 80%, and they represent a risk factor for iridocyclitis. Children with the oligoarthritis subtype generally have the best outcome (89); however, sight-threatening, clinically silent uveitis develops in the first 4 years from diagnosis. Regular ophthalmology follow-up is essential (111).
Polyarthritis must affect five or more joints in the first 6 months of the disease. RF-positive polyarthritis mainly affects adolescent girls, with a symmetrical pattern, and is the same as adult RF-positive disease (97). By 5 years from onset, severe deforming arthritis is generally present (98). RF-negative polyarthritis is a more heterogeneous group with more variable outcome. Approximately 20% to 40% of those affected are ANA-positive, and chronic uveitis is found in 5% to 20% (97); it is believed by some authors that this entity represents a later stage of early-onset oligoarthritis (112). Future versions of the ILAR classification of JIA may explore this more fully.
Psoriatic arthritis accounts for about 5% of JIA and requires the simultaneous presence of arthritis and the typical psoriatic rash, or if the rash is absent, arthritis plus two of the following: positive family history of psoriasis in a first-degree relative, dactylitis, and nail pitting. Psoriatic disease in children before the age of 5 years appears to be more difficult to control than in an older subset of children, with a median of 9.5 years (92).
Enthesitis-related arthritis affects males after the age of 6 years (97,98) and most children are human leukocyte antigen (HLA)-B27-positive. The most common sites of enthesitis are the calcaneal insertion of the Achilles tendon, plantar fascia, and tarsal area. Arthritis commonly affects the joints of the lower extremities. Unlike other JIA subsets, hip involvement is common at disease presentation.
These children may progress to fulfill criteria for ankylosing spondylitis, reactive arthritis, or arthritis associated with inflammatory bowel disease. Uveitis is also a clinical problem in this subset, but it is usually sudden in onset, symptomatic, and more unilateral than in children with other JIA subsets (92).
Juvenile ankylosing spondylitis, not considered part of the JIA subclassification; mainly affects adolescent boys; is strongly associated with HLA-B27; and manifests as an asymmetric, often episodic, oligoarthritis in the lower limbs. Later on, bilateral sacroiliac joints become involved, and progression of the disease can lead to the characteristic "bamboo" spine on radiographic images secondary to ankylosis of spinal joints. In children, peripheral arthritis and enthesitis present early in the disease, but sacroiliac and spine joints are not involved until many years later (113). Rehabilitation involves maintaining spinal ROM through extension exercises, strengthening hip extensors and quadriceps muscles, custom shoe inserts to relieve pain, and deep breathing exercises to maximize chest expansion. Because of the chronic course of the disease, the child and parents should not restrict age-appropriate social and recreational activities (113).
Inflammatory bowel associated arthritis occurs in approximately 10% to 20% of children with ulcerative colitis and Crohn's disease. The arthritis usually affects a few joints and may be associated with spondylitis; erythema nodosum and growth failure may occur.
This subset is not a separate entity, but is more of a catchall category for those children who do not satisfy inclusion criteria for any category, or who meet criteria in more than one category.