What is juvenile idiopathic arthritis?
Información en español disponible en: Artritis juvenil
Considered the most common form of arthritis, juvenile idiopathic arthritis (JIA) begins before age 16 and involves swelling in one or more joints lasting at least six weeks. JIA includes several types of arthritis previously known as JRA. In recent years, though, researchers have developed a more sophisticated understanding of the differences between specific types of arthritis, and the terminology and definition of the disease has shifted.
One reason for this shift is that JRA is not – as the term implies – simply a pint-sized replica of the condition that affects adults. In fact, it’s believed that only about 10 percent of children have a disease that closely mirrors rheumatoid arthritis in adults. Researchers also concluded that the JRA category was drawn too narrowly and should include some related diagnoses, such as ankylosing spondylitis.
JIA may include a variety of symptoms, such as muscle and soft tissue tightening, bone erosion, joint misalignment and changes in growth patterns. Not all symptoms are shared by all children with the disease. Moreover, the symptoms of JIA can change from day to day.
Diagnosis of JIA is based on physical exam as well as lab tests and medical history. In addition to watching for symptoms for at least six weeks, your child’s doctor will wait to see how her symptoms unfold during the first six months after onset. The number of joints affected during those first six months determines the diagnosis. In addition, the JIA criteria also rely on other results, such as those from the rheumatoid factor blood test, to help further diagnose children within the subsets of JIA.
There are nine types of juvenile idiopathic arthritis. Following are descriptions of each subset:
Oligoarthritis: Formerly known as pauciarticular this type, is diagnosed when four or fewer joints – “pauci” and “oligo” mean “few” – are involved within the first six months. It’s particularly common in Caucasian children and accounts for about 40 percent of new JIA cases in that group. Girls are more likely to be diagnosed with oligoarthritis and to experience eye inflammation, a condition called uveitis. Oligoarthritis typically develops by age 6. At diagnosis, frequently only one joint is involved and it’s commonly a joint in the leg, such as the knee or the ankle.
If your child also tests positive for a particular antibody in the blood, called the antinuclear antibody (ANA), she faces the greatest risk of developing eye inflammation and will be monitored very closely for eye problems. Compared with other types of JIA, children with oligoarthritis are less vulnerable to severe problems with joint function.
Under the JIA criteria, oligoarthritis is broken into two groups. Children in which the arthritis is confined to four or fewer limbs fall into a category called persistent oligoarthritis. After the six-month window, some children will develop symptoms in additional limbs and will be diagnosed with extended oligoarthritis.
Polyarthritis: This type of JIA – “poly” means “many” – occurs when five or more joints are involved during the first six months. Roughly 25 percent of children with JIA have polyarthritis. Like oligoarthritis, it’s more common in girls. But its onset can occur any time in childhood. Both large and small joints, such as the fingers and toes, may be involved. Your child also may experience arthritis in the neck or the jaw, making chewing and opening her mouth more difficult.
Unlike oligoarthritis, polyarthritis more frequently affects joints on both sides of the body, such as the right and the left knees. Children with polyarthritis might face a lower risk of eye inflammation, but will still need to see an ophthalmologist on a regular basis.
The JIA criteria also sub-divides children with polyarthritis into two categories, those who test positive for rheumatoid factor (RF) – an antibody found in the blood – and those who don’t. The RF-positive form of the disease usually emerges in the elementary school years or later. It’s the type most similar to adult rheumatoid arthritis. Children with RF-positive polyarthritis are typically more vulnerable to severe disease and related joint erosion than those who test negative for rheumatoid factor.
Systemic: Involving about 10 percent of JIA cases, systemic arthritis affects the entire body, beyond just the joints. Both boys and girls are equally vulnerable. Although symptoms can start any time during childhood, they generally emerge by or in elementary school years.
The first sign might be a stubborn fever, sometimes appearing weeks or months before your child complains of any joint discomfort or mobility issues. The fever can be quite high, appearing once or twice daily, before returning to normal. Your child might seem, by all indications, fine in between. Fevers also may be accompanied by a faint rash, one that ebbs and flares over the course of days. Often described as pinkish or salmon-colored, it’s not contagious.
Since this illness can affect the entire body, inflammation may occur elsewhere, enlarging the spleen or irritating the membranes that cover the lungs or heart. In many cases, the fever and other systemic symptoms fade over time. Eye inflammation isn't common with systemic arthritis, but your child’s vision will still need to be checked.
The condition can influence your child’s growth and appetite, making good nutrition a high priority. But the course of the disease, including the number of joints involved, can be highly variable and individual. Only over time will your child’s doctor have a better sense of the challenges she faces.
Enthesitis-related arthritis: This type, which wasn’t included under the JRA criteria, involves inflammation of the entheses, sites where tendons attach to the bone. Boys are more often diagnosed. The arthritis can be mild, involving four or fewer joints in roughly half of cases. In some children, arthritis can move to the spine. Frequently, they test positive for the HLA-B27 gene.
Over time, your child may develop one of the various conditions known as juvenile spondyloarthropathies, which may but do not necessarily affect the spine. Some of those diseases include: juvenile ankylosing spondylitis, arthritis associated with inflammatory bowel disease and reactive arthritis.
Juvenile Psoriatic Arthritis: In this form of arthritis, the skin condition called psoriasis may precede or follow the symptoms of psoriatic arthritis, sometimes by years. The rash may appear as a scaly red rash, emerging behind the ears or on the eye lids, elbows, knees or scalp. Your child may have a family history of psoriasis. Another common sign: a pitting or unusual ridging on the fingernails.
Other: Any arthritis of unknown cause, with symptoms continuing at least six weeks, that doesn’t meet criteria for any one type of JIA or involves symptoms than span two or more types.