What kind of disease is it?
Juvenile idiopathic arthritis (JIA) is a chronic disease characterized by persistent arthritis, typically characterized by pain, swelling and limited movement. The term “idiopathic” means that we do not know the cause of the disease, and “juvenile” in this context means that the symptoms appear at an age younger than 16 years.
What does chronic mean?
A disease is considered chronic when regular treatment of the disease does not lead to an immediate recovery, but only to an improvement in symptoms and laboratory results. This means that when the disease is diagnosed, it is not possible to say how long the child’s illness is going to last.
Is it common?
JIA is a rare disease with an incidence of about 80-90 per 100,000 children.
What are the causes of this disease?
Our immune system protects us from infections (viruses and bacteria). The immune system is able to recognize foreign and potentially dangerous and to differentiate and remove foreign tissues from its own.
There is definite evidence that chronic arthritis is a secondary response of the immune system (for reasons that are not yet clear), due to a partial loss of the immune system’s ability to distinguish between “foreign” and “own” cells, thus destroying its own joint components. It is also due to the partial loss of the immune system’s ability to distinguish between “foreign” and “own” cells, thus destroying its own joint components. Therefore, these diseases, such as JIA, are also called “autoimmune diseases”, meaning that the immune system reacts to its own body organs. However, as with most chronic inflammatory diseases in humans, the mechanism that causes JIA is unclear.
Is it a genetic disease?
JIA is not a genetic disease because it is not passed directly from parents to their children. However, there are genetic factors that contribute to susceptibility to the disease, and most of these factors are still being studied.
What is recognized by scientists is that the disease is multifactorial. This means that an individual’s genetic susceptibility and environmental factors (possibly infection) combine to cause the disease. Even when a susceptibility to the disease exists, it is rare to see two children in the same family with the disease.
How is JIA diagnosed?
A doctor diagnoses JIA when the following conditions are met: the age of onset is less than 16 years, the arthritis lasts more than 6 weeks (mainly to rule out temporary arthritis after a viral infection), and the cause of onset is unclear (meaning that all diseases that can cause arthritis have been ruled out).
In other words, the term JIA encompasses all persistent arthritis of childhood onset that has an unclear cause. In JIA, the different forms of arthritis have been identified (see below). Therefore, the diagnosis of JIA is based on persistent arthritis and carefully excludes any other disease by history, physical examination, and laboratory tests.
What changes have occurred in the joint?
The synovial membrane (usually very thin) surrounding the joint is thickened, with a large infiltration of inflammatory cells and increased fluid in the synovial cavity. These changes cause swelling, pain and limited movement of the joint. A characteristic manifestation of arthritis is joint stiffness, which occurs after a long period of rest and, therefore, tends to occur especially in the morning (morning stiffness).
In order to reduce pain, the affected child often keeps the joint in a semi-flexed position, which is called the “pain relief position” to emphasize that the position is maintained to reduce pain.
Without proper treatment, arthritis can be caused by two mechanisms of injury.
1. thickening of the synovial membrane (with the formation of so-called vascular opacities), which causes the destruction of articular cartilage and bone due to the release of various substances.
2. maintenance of the painful position for a long time, causing muscle contracture and flexion of the muscles or soft tissues, resulting in flexion deformity.
Is this disease divided into different types?
There are several different types of JIA. Their main differences are the presence of systemic symptoms, such as fever, rash, and pericarditis (systemic JIA), and the number of joints involved (oligoarthritic and polyarthritic JIA). According to the regulations, the different types of JIA are defined according to the manifestations of the disease at the beginning of the 6 months of illness, so these types of disease are also called types of morbidity.
Systemic JIA. In addition to arthritis, there are systemic manifestations (systemic means that all organs of the body may be involved). The main systemic symptom is a high fever, often accompanied by a pink rash, which appears in the presence of a high fever. Other symptoms are enlarged liver and spleen lymph nodes, pericarditis, and pleurisy. Arthritis is often polyarthritic (five or more joints are involved) and can present at the onset of the disease or later. This type can present in children of any age.
Approximately half of the patients are characterized by systemic manifestations, and these patients have a better long-term prognosis; in the other half, the systemic manifestations gradually subside after a period of time and the joint symptoms become more important. In a few cases, systemic symptoms persist together with joint manifestations.
Systemic JIA accounts for less than 10% of all JIAs and occurs mainly in children; it is rare in adults.
Polyarticular JIA is characterized by the involvement of five or more joints during the first six months of the disease, without the systemic manifestations mentioned above. Polyarthritic JIA is divided into two types: RF negative and RF positive, based on the presence of an autoantibody, rheumatoid factor (RF), in the blood.
1) RF-positive polyarthritic JIA. This type is rare in children (less than 5% of all JIA patients). It is considered to be the same as RF-positive rheumatoid arthritis in adults (the main type of chronic arthritis in adults). It often presents as a symmetric arthritis that initially affects mainly the small joints of the hands and feet, and then progresses to other joints. The age of onset is younger than 10 years and is more common in girls than boys. This is a severe form of arthritis.
(2) RF-negative polyarthritic JIA. This type accounts for about 15-20% of all JIA patients. It is a complex group of forms that may include different diseases. This type can occur at any age and its prognosis is very complex.
The oligoarticular form of JIA is characterized by the involvement of fewer than 5 joints at the beginning of the 6 months of the disease, without the manifestations of the systemic form mentioned above. It often involves large joints (such as the knee and ankle) and is asymmetric. Sometimes only one joint is involved (monoarticular type). In some patients, the number of joints involved increases to 5 or more after 6 months of disease.
The oligoarticular form often starts at an age younger than 6 years, and is more common in girls. With appropriate treatment, the prognosis is good for patients whose disease is limited to a few joints; the prognosis for those who develop the extended form is variable.
An important ocular complication that may complicate the disease in some patients is inflammation of the anterior uvea (anterior uveitis), a membrane lining the inside of the eye that provides the blood supply to the eye. Because the anterior uvea is made up of the iris and ciliary body, this complication is also called chronic anterior uveitis or chronic iridocyclitis.
If left undiagnosed or untreated, anterior uveitis can progress and cause very serious eye damage. Therefore, it is very important to be aware of this complication early. Because there is no eye congestion when anterior uveitis develops and the child does not feel blurred vision, the condition is not likely to be recognized by parents or general practitioners. Therefore, it is important for children with risk factors to have regular eye exams, every 3 months by an ophthalmologist with a slit lamp.
The oligoarthritic type is the most common type of JIA (50% of patients.) The type I with positive ANA (see laboratory tests) and associated iridocyclitis is a special type in children and is not seen in adults.
Psoriatic arthritis is characterized by the presence of arthritis associated with psoriasis. Psoriasis is a skin disease with skin changes that are mainly confined to the elbow and knee joints and appear as flaky scales. The skin changes may precede or follow arthritis. This condition is complex in terms of clinical presentation and prognosis.
Arthritis associated with enthesitis The most common manifestation of this type is oligoarthritis, which primarily affects the large joints of the lower extremities and is associated with tendon enthesitis. Tendonitis is an inflammation of the point of attachment of the tendon, which is the location where the tendon attaches to the bone. The most common site of pain in this type is confined to the inner part of the foot, posterior or inferior to the heel. Sometimes, these patients may have acute anterior uveitis, which is not as common as the oligoarthritic type, where there can be eye congestion, tearing, and photophobia. Most patients have positive laboratory tests for HLA-B27. The disease is predominantly male and often develops after the age of 7-8 years. The clinical course of this type is variable, with some patients being able to remit with treatment and others having sacroiliac joint (posterior lumbar) involvement early in the course of the disease, which tends to progress to the medial skeleton (spinal region). In fact, this type belongs to a group of diseases that tend to appear in adults and are called ankylosing spondylitis because of their ability to affect the spine.
How is chronic iridocyclitis caused? Is it related to arthritis?
In patients with arthritis, the inflammation of the eye is caused by an abnormal immune response against the eye (autoimmunity). However, the exact mechanism is not known. This type is commonly seen in the oligoarthritic type, at a younger age, with positive laboratory tests for antinuclear antibodies (ANA).
It is not clear how arthritis causes the eye lesions, but it is important to remember that arthritis and iridocyclitis are sometimes independent, so it is important to continue to have regular slit lamp exams even if the arthritis has resolved. The course of iridocyclitis can have intermittent recurrences, and recurrences are also unrelated to arthritis.
Iridocyclitis often follows or coincides with arthritis, and very rarely, iridocyclitis precedes arthritis. This is unfortunate because iridocyclitis is asymptomatic and by the time these patients are diagnosed, it is no longer early but has caused something symptomatic, such as visual impairment.
Is there a difference between JIA and RA in adults?
In general, there is a difference; the RF-positive polyarthritic form accounts for 70% of rheumatoid arthritis in adults, while it accounts for less than 5% of JIA. The early-onset oligoarthritic form accounts for about 50% of JIAs, whereas it is not seen in adults. Systemic arthritis is unique to children and is rarely seen in adults.
What kind of laboratory tests are needed?
Some laboratory tests are useful, some related to the clinical presentation and some to help better staging of JIA and to identify whether the patient is at risk of developing certain complications, such as iridocyclitis.
Rheumatoid factor (RF): is an autoantibody, and persistently high levels of positive RF are seen only in the polyarthritic type of JIA, which in children is equivalent to RF-positive adult rheumatoid arthritis.
Anti-nuclear antibodies (ANA): ANA positivity is common in patients with early-onset oligoarthritic JIA; ANA positivity indicates that these patients are at risk for developing chronic iridocyclitis and should be referred for regular (every 3 months) ocular slit lamp examinations.
HLA-B27, a cell surface antigen, is positive in 80% of patients with arthritis associated with attachment sites, whereas its frequency in the general healthy population is very low (5-8%).
Other laboratory tests such as sedimentation (ESR) or C-reactive protein (CRP) can detect the degree of general inflammatory response and can be helpful in the treatment of the disease, but treatment depends more on the clinical presentation than on laboratory tests.
Depending on the drug used, patients need to undergo regular laboratory tests (e.g., blood work, liver function, urine routine) to monitor potential drug toxicity. Regular x-ray examinations are useful to evaluate the progression of the disease and thus to change the treatment plan.