juvenile idiopathic arthritis
Juvenile idiopathic arthritis (JIA), also known as juvenile rheumatoid arthritis, is the most common chronic arthritic disease of childhood and corresponds to a group of different subtypes.
The estimated incidence is ~13 per 100,000 per annum . By definition, symptoms must start before 16 years of age. Females are more affected with F:M = 2:1.
Oligoarticular or polyarticular arthritis of a duration of six weeks or longer must be present to diagnose JIA.
Patients may present with an acute onset of symptoms or a more gradual onset. Symptoms are often worse in the morning but typically persist to some extent throughout the day.
In patients with systemic onset (also known as Still disease), intermittent spiking fevers are typically noted, which helps distinguish JIA from other diseases such as infection, other inflammatory diseases and malignancy. Migratory salmon colored light pink rash involving the trunk and/or extremities and hepatosplenomegaly are also frequently observed in patients with systemic onset.
A proportion of patients have serum rheumatoid factor .
There are several subtypes of JIA
- oligoarticular JIA
- affected ≤4 joints in the first six months of illness
- peak age: 1-6 years
- mainly affects medium and large joints
- polyarticular JIA
- ≥5 joints are affected
- peak age: 1-4 years; 7-10 years
- mainly affects small and medium joints
- systemic onset JIA (Still's disease, not to be confused with adult onset Still's disease)
- see above
- arthritis may present weeks to months after the onset of systemic symptoms
Imaging shows a varied spectrum of involvement, based on the severity and duration of the disease. There is usually a predilection for large joints rather than small joints.
Findings on x-ray include soft tissue swelling, osteopenia, loss of joint space, erosions, growth disturbances (epiphyseal overgrowth or "ballooning") and joint subluxation.
Cervical spine radiographs may demonstrate:
- atlantoaxial subluxation
- odontoid erosions
- ankylosis, especially of the facet joints
MRI may show synovial hypertrophy, joint effusions and rice bodies , as well as osseous and cartilaginous erosions. Active synovitis is characterized by enhancement on T1-weighted gadolinium contrast studies.