Juvenile idiopathic arthritis (JIA) is the most common chronic arthritis of children. It is one of the most common chronic illnesses of childhood and a major cause of short-term and long-term functional disability and eye disease leading to blindness. JIA is the term used throughout this article in preference to juvenile rheumatoid arthritis (JRA). [1, 2]
Although it has been customary to refer to JIA as one disease, it is almost certainly 3 or more diseases, which may have the same cause, different causes, or a closely related series of host responses. The course of JIA is unpredictable; it tends to be most predictable after the pattern of the disease is established.
See the images of JIA below.
For more information about JIA, see Juvenile Rheumatoid Arthritis.
Criteria and classification
Those developed by the American College of Radiology (ACR)
Those of the European League against Rheumatism (EULAR)
Those proposed by the International League of Associations for Rheumatology (ILAR)
The ACR criteria define arthritis, the age limit (< 16 y), and the duration of disease (>6 mo) necessary for a diagnosis. They also recognize 3 types of onset: polyarticular, pauciarticular, and systemic.
The EULAR proposed the term juvenile chronic arthritis (JCA) for the heterogeneous group of disorders that manifest as juvenile arthritis. The diagnosis requires that the arthritis begins before the age of 16 years, that it lasts for at least 6 weeks, and that other diseases are excluded.
The ILAR criteria are currently the preferred classification system. The aim is to provide a unified classification system. The ILAR classification of JIA includes the following features:
Persistent or extended oligoarthritis
Rheumatoid factor (RF)–positive polyarthritis
Other: The disease does not meet criteria for any of the other subgroups, or it meets more than 1 criterion (and therefore could be classified in a number of subgroups)
Basic radiographic changes include the following:
Osteopenia and/or osteoporosis
Intra-articular bony ankylosis
Epiphyseal compression fracture
The main limitation of conventional radiography is that it does not allow direct examination of the articular cartilage, synovium, and other important noncalcified structures in a joint.
CT scanning is the best method for analyzing some regions with complex anatomy, such as the sacroiliac joint and occasionally the hip, shoulder, or temporomandibular joints. MRI has now largely superseded CT in the overall assessment of JIA. The major disadvantage of CT scanning is that it involves a substantial radiation dose.
Magnetic Resonance Imaging
To improve visualization of synovial hypertrophy and improve detection of cartilaginous erosions when an inflammatory arthritis is suspected, contrast-enhanced sequences should be performed. MRI provides the most sensitive radiologic indicator of disease activity. MRI can depict synovial hypertrophy, define soft tissue swelling, and demonstrate excellent detail of the status of articular cartilage and overall joint integrity. [7, 9, 10, 11, 12, 13, 14, 15, 16, 8]
See the MRI image below.
Synovitis and a joint effusion may have similar hyperintensity on T2-weighted (T2W) and short-tau inversion recovery (STIR) images. Therefore, gadolinium-enhanced T1-weighted (T1W) MRIs are necessary to accurately define active synovitis.
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic, Nephrogenic Fibrosing Dermopathy. NSF/NFD has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Some enthusiasts claim that ultrasonography is more sensitive than plain radiography in the detection of cartilage erosions and effusions, but ultrasonography is notoriously operator dependent.
On sonograms, inflamed synovium can appear as an area of mixed echogenicity lining the articular cartilage. Serial measurements of synovial thickness and effusion volumes have been used to monitor disease progression. The vascularity of the synovium can be assessed with Doppler flow studies. 
Bone scanning remains an effective method with high sensitivity and low specificity. Bone scanning may be combined with single photon emission CT (SPECT) to increase sensitivity in the one or more foci of abnormal isotopic accumulation.
The major application of bone scintigraphy in people with juvenile idiopathic arthritis (JIA) is in determining the distribution of disease. The major disadvantage of bone scintigraphy is its substantial radiation dose.