Juvenile arthritis (JA) is characterized by an overactive immune system, resulting in inflammation and damage to healthy tissues, such as joints. Because the cause of this disease is unknown, it is often referred to as juvenile idiopathic arthritis (JIA).
There are a number of different types of JA, and each is marked by differences in disease symptoms, severity, and prognosis.
Oligoarticular JA (oligoarthritis) is the most common form of JA, found in about two out of every three cases. This form is determined to be oligoarthritis if four or fewer joints are affected within the first six months of JA diagnosis. It is more common in boys than girls, and is also be referred to as persistent oligoarthritis.
Oligoarthritis symptoms are generally mild, and often little or no permanent joint damage occurs. Commonly, large joints (such as the knees, ankles, and elbows) are affected, and there is a high chance of developing chronic anterior uveitis (eye inflammation). Chronic anterior uveitis can damage vision if untreated but does not tend to result in pain or redness, so regular eye exams in children with oligoarthritis are essential. Those testing positive for antinuclear antibody (ANA) in their blood are at greatest risk of developing chronic anterior uveitis.
If, after the initial six-month period, symptoms develop in more that four joints, the disease may be classed as extended oligoarthritis. This more severe form of oligoarthritis can damage joints and may require more aggressive treatment with medication.
Polyarticular JA (or polyarthritis) makes up around 25 percent of all JA diagnoses. It can have a sudden onset and progress to multiple joints in a matter of months. Polyarthritis is marked by five or more joints being affected within the first six months of diagnosis. Often, smaller joints such as those of the fingers and toes are the first to be affected, but the wrists, ankles, hips, knees, neck, and jaw can also be involved. Polyarthritis can cause painful swelling in these joints and be accompanied by fever and nausea.
This type of JA can be “rheumatoid positive” or “rheumatoid negative,” based on blood tests for a particular protein, called rheumatoid factor (RF), that the immune system produces as part of the damaging immune response seen in JA. RF positive patients are more susceptible to severe joint damage than those who test negative.
Systemic-onset JA is diagnosed in around 10 percent of all JA patients. This type of JA can be very severe, with inflammation affecting the entire body rather than just the joints. Patients with systemic-onset JA may experience constant joint pain, fever, tiredness, rashes, loss of appetite, and weight loss. Systemic-onset JA can be difficult to diagnose early , as joint problems are not typically the first symptoms to occur.
Inflammation can affect organs, including the spleen, liver, and in rare cases, the covering of the heart. Glands in the neck, underarms, and groin may also swell, becoming enlarged.
Juvenile psoriatic arthritis
Juvenile psoriatic arthritis is a combination of JA and a skin condition called psoriasis, which can be evident as a scaly red rash often behind the ears or on the eyelids, elbows, knees, back, buttocks, or scalp. The arthritic and psoriatic symptoms may appear at different times, sometimes even years apart. A common symptom of juvenile psoriatic arthritis is “pitting,” or the disocoloration and thickening, of the nails.
Enthesitis-related JA tends to be more common in boys than girls and is also referred to as spondyloarthritis. It causes inflammation at the points where tendons attach to the bone (the connective tissues, or entheses, between tendons and bone), especially those in the leg and spine. This type of JA is often marked by stiffness in the lower back and neck that can carry into adulthood, and it carries a higher risk of a person developing acute uveitis.
Patients with enthesitis-related JA frequently have a particular genetic marker called HLA-B27, which is also associated with inflammatory bowel disease.
When JA is found but does not fit into one of the above subtypes, or if there is a combination of symptoms from more than one subtype, a diagnosis of “undifferentiated arthritis” may be given.
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