Juvenile idiopathic arthritis (JIA) is the mostcommon rheumatic disease in children.
Many children with JIA have active disease thatcan persist into adulthood and may result in shortor long term morbidity.
JIA is an arthritis of unknown aetiology that begins before the sixteenth birthday and persists for atleast 6 weeks other conditions being excluded. The incidence of JIA is 2 to 20 per 100,000 and the prevalence 16 to 150 per 100,000. The minimal incidence of the disease was 9.2 per 100,000 children at risk in a report from Michigan; in Finland, 18.2 per 100,000; and in Sweden 11 per 100,000. The prevalence in Michigan was 65 per 100,000 and 86 per 100,000 in Swedish study. In India constituted 41% among patients reported from a single tertiary referral centre. JIA can be oligoarticular (60%), systemic onset (10%), polyarticular (30%) and enthesitis related. While oligoarticular being 40% of newly diagnosed among Caucasian population, polyarticular is predominant in African, East Indian and Indian population. In a study of 495 JIA cases from Chennai, South India systemic onset was 105 (21.2%) oligo arthritis 75 (15.2%), polyarthritis 175 (35.3%), enthesitis related arthritis 131 (26.46%), psoriatic arthritis (1.6%) and undifferentiated arthritis 1 (0.2%).
JIA is an autoimmune disease involving innate immune system, T cells, immune complexes, cytokines etc. with complex genetic traits. Both the IL2RA / CD 25 gene and VTCN1 gene have been implicated as JIA susceptibility loci.
JIA has same histological characteristics as RA manifesting with villous hypertrophy of synovium and hyperplasia of the synovial lining layer. Pannus formation may result and articular cartilage and bone gets eroded.
Oligoarthritis JIA :
In this type, girls are more commonly affected and usually occurs under the age of 6 years. It involves mainly knees, ankles and joints will be swollen but pain may not be severe.
A limp may be the only sign of the disease. ANA positivity can occur in this type with the risk of developing asymptomatic chronic anterior uveitis (inflammation of iris and ciliary body).
Polyarthritis JIA :
Rheumatoid factor positive type usually affects girls in late childhood. Because of the development of severe arthritis with bony erosion and extra articular manifestation including rheumatoid nodules, it is called adult type of JIA. The manifestations will be symmetrical polyarthritis involving larger and smaller joints including metacarpophalangeal, interphalangeal, temporomandibular joints and cervical spine. Rheumatoid factor negative type occurs throughout childhood and the disease severity will be less. ANA positivity can be associated with chronic anterior uveitis.
Enthesitis related arthritis :
This type is characterised by enthesitis at the site of insertion of tendoachilles, plantar fascia and also in tarsal area. Asymmetrical arthritis predominantly affecting the lower limbs will occur. Hip joint involvement is not uncommon and erosion at the site of enthesitis can be found. Eye involvement as symptomatic recurrent acute anterior uveitis is a frequent extra articular manifestation. Boys above the age of 6 years are affected and are often HLA B27 positive. Many children in this type may develop acroiliac and spinal joint involvement.
Ultimately some develop one of the spondyloarthropathies like Juvenile onset ankylosing spondylitis and undifferentiated spondyloarthropathy.
Systemic onset JIA (SoJIA) :
This type of onset is also known as Still's disease, who made earliest formal description of Juvenile Arthritis in 1897. SOJIA constitute 10-20% of all JIA but highest morbidity occurs in this type. There is equal sex incidence and can occur at any age during childhood. The characteristic of fever will be one or two spikes a day in the evening or early morning lasting for few hours, comes back to normal and subside on its own, whether treatment is given or not.
During the peak of the fever evan escingmaculopapular rash occurs predominantly in the covered portion of the body. The other manifestations are lymphadenopathy, hepatosplenomegaly, pericarditis and rarely myocarditis. The clinical course is variable. Systemic features like fever may precede arthritis by weeks or months. In 50% of cases the extra articular features subside during initial years of the disease. The polyarticular course of the disease involving larger and smaller joints will be progressive in nature. Many patients who have persistent active disease, develop cervical spine involvement that will lead on to ankylosis.
Linear growth is usually retarded during active disease. There is often delayed puberty and development of secondary sexual characteristics. Osteopenia resulting in increased risk of fracture in adulthood is a major determinant of functional outcome. One of the most determinant complication is chronic nongranulomatous uveitis specially in girls who are ANA seropositive with oligoarthritis developing at a young age.
Sacroiliac arthritis is not characterized by the degree of reactive sclerosis as in juvenile ankylosing spondylitis.
JIA has a list of differentials as rheumatic fever, SLE, spondyloarthropathy, infectious arthritis, serum sickness, inflammatory enteropathy and hematologic diseases.
Laboratory tests should not be solely relied upon to make the diagnosis of JIA. Children with JIA usually have normochromic normocytic anemia, polymorphonuclear leucocytosis, thrombocytosis and elevation of erythrocyte sedimentation rate and C-reactive protein. RF will be positive in less number of patients with JIA (polyarticular RF positive). Anti-Cyclic citrulinated peptide (Anti.CCP) is positive mostlyin patients with RF positivity. ANA can be positive mostly in oligoarticular type and less frequently in polyarticular type. HLA-B27 can be positive in Enthesitis Related Arthritis (ERA). False positive Anti Streptolysin-O, can occur due to inflammation and polyclonal B cell activation- anamnestic reaction.
X-rays show soft tissue swelling, subchondral osteoporosis, periosteal elevation and rarely bony erosion. Cervical spine x-ray is useful in diagnosing fusion and atlanto axial subluxation. Ultrasound with high power Doppler and Magnetic resonance imaging are useful in the early detection of synovitis and erosions.
In the treatment arm amentarium there are NSAIDs, IA steroid, hydroxychloroquine, methotrexate, sulphasalazine, oral or IV steroids, leflunomide, cyclosporine A, IV immunoglobulin and TNF alpha blockers.
Indian studies on JIA are limited and we need to strengthen our Indian database on JIA pattern that is characteristic and representative of Indian pediatric population.