Juvenile idiopathic arthritis is the most common rheumatic disease with no clear origin during childhood. The prevalence of this disease is around 1.6 to 23 cases per 100,000 children under 16 years of age and 3.8 to 400 cases per 100,000 adolescents over 16. Depending on the regions consulted, there are many disparities.
In any case, it should be noted that the term juvenile idiopathic arthritis (JIA) does not designate a single clinical picture, but rather refers to several subtypes of pathologies. It is important to bear in mind that this concept encompasses the most typical forms of pediatric chronic inflammatory arthritis.
Of all the variants, oligoarthritis is the most common, accounting for 50-60% of cases. If you want to know more about this heterogeneous group of diseases, read on.
Juvenile idiopathic arthritis types and their symptoms (JIA)
As indicated by the StatPearls portal, juvenile idiopathic arthritis is defined as a heterogeneous group of inflammatory arthritis with no known cause that affects children under 16 years of age and lasts for 6 weeks or longer. Before, the term was split into 2 different concepts: juvenile chronic arthritis (JCA) and juvenile rheumatoid arthritis (JRA). Since 1995 they were unified.
Following the consensus devised in 2001 by the International League of Associations for Rheumatology (ILAR), it was stipulated that there are 7 types of juvenile idiopathic arthritis. We tell you its peculiarities in the following lines.
1. Oligoarthritis
It is the cause of 50 to 60% of the clinical pictures of juvenile idiopathic arthritis. This variant affects 1 to 4 joints, with a focus on the largest ones (elbows, wrists, or knees). It is the most common in early childhood, as it shows an epidemiological peak at 2-4 years of age.
In addition, it has 3 other subforms, depending on the interval of appearance. They are as follows:
- Typical oligoarthritis: does not extend beyond 6 months.
- Persistent: lasts the entire pathological course
- Extended: exceeds 6 months in duration.
2. Positive polyarthritis for rheumatoid factor (RF)
Rheumatoid factor can be considered a protective IgM type antibody, as it is found in high concentrations in the blood during persistent infections. In a normal situation, this molecule forms complexes that will be phagocytosed by inflammatory cells, helping the immune system.
Unfortunately, genetic mutations can cause this factor to be over-expressed and have prolonged inflammatory activity. Thus, 80% of patients with rheumatoid arthritis are RF positive. For this reason, juvenile polyarthritis can also be associated with rheumatoid factor dysfunction.
Rheumatoid factor-positive polyarthritis affects only 5-10% of children with JIA, so it is not considered common. As indicated by the American College of Rheumatology (ACR), this variant is typical of young people between 11 and 16 years old, who begin with nonspecific symptoms. It affects 5 or more joints during the first 6 months.
As a differential character, it should be noted that it is symmetric. If the extremity of one body plane becomes inflamed, so does the other side. It usually affects small joints, such as the wrists and the joint structures of the hands and feet.
3. Rheumatoid factor (RF) negative polyarthritis
This variant affects 20% of children with IAJ, making it the second most common, after oligoarthritis. Like the positive RF, it takes five joints or more during the first 6 months, but is negative for the rheumatoid factor (RF) test.
4. Psoriatic arthritis
It occurs in only 2% of patients with IAJ and is biphasic, that is, it has 2 epidemiological peaks (one at 2-4 years and another at 9-11 years). As its name indicates, in this case the joint pain is accompanied by psoriasis, a pathology that occurs with skin lesions in the form of scaling.
This time, the patient’s immune system wrongly redirects his efforts. CD4 + T cells release cytokines and trigger inflammatory events, causing the outer epidermal layer to grow larger than it should (local epidermal hyperplasia). In turn, it causes joint inflammation.
For psoriatic arthritis to be considered as such, it must meet at least 2 of the following parameters, in addition to joint pain:
- Dactylitis: inflammation of the fingers and toes. It often occurs in the fingers of the entire affected limb simultaneously.
- Nail dimples: typical lesions visible at the level of the nails.
- Onycholysis: one or more nails are separated from the nail bed.
- A family history of first-degree psoriasis.
5. Systemic arthritis
As indicated by the American Academy of Pediatrics (AAP), systemic arthritis affects 5-15% of patients with JIA and, unlike the rest, there is no clear predilection according to gender and age. This variant can affect the entire body (at least one joint) and is accompanied by daily fever, present for at least 3 days.
The fever shows up in peaks, rising to 40 degrees Celsius at times. Swollen lymph nodes, evanescent erythematous rashes, hepatomegaly (enlargement of the liver), splenomegaly (enlargement of the spleen), or serositis (inflammation of adipose tissues) may also be noted.
For a JIA to be systemic, fever and one of these accessory signs must be present, beyond joint pain.
6. Arthritis related to enthesitis
It represents 10-15% of patients with JIA and is observed in children older than 6 years of age. Enthesitis is an inflammatory process of enthesis, that is, the insertion area of a tendon with a bone, a muscle or a ligament. It affects the knees, hips, pelvis, and even the digestive tract (such as ulcerative colitis).
This variant is associated with a genetic factor, HLA-B27. Those who are positive for it have arthritis related to enthesitis.
7. Undifferentiated arthritis
It represents approximately 10% of the total cases. It does not respond to any of the qualifying criteria mentioned above. Also it can be a type of JIA that meets the criteria of 2 or more of the listed categories.
Causes and risk factors
As indicated by the Rheumathology and Therapy Journal, the cause of juvenile idiopathic arthritis remains a mystery. Many of the variants are believed to be due to misdirected immune responses after an exogenous trigger, such as a severe infection. Anyway, these lands are speculative.
The role of pathogens such as parvovirus, Epstein-Barr virus, enteric bacteria and other possible triggers of JIA is currently being investigated, although the results are not conclusive. Childhood infections, stress and trauma appear to be the 3 factors that, together, lead to idiopathic arthritis.
However, this pathological group also has a clear genetic component. There are variations of human leukocyte antigens (HLA) and their genes that could predispose to certain types of JIA, in addition to other immune events, such as uveitis.
Possible complications
According to the PubMed medical portal, chronic anterior uveitis is the most common complication, as it occurs in 10-30% of all cases. This pathology involves inflammation of the front part of the eye, in the form of attacks that last a few days or weeks and end with the relevant treatment.
In many cases, the cause of uveitis is unknown, but in others it is linked to the same failed autoimmune reactions that trigger the phenomena of arthritis. It is necessary to prevent this complication, as it can lead to glaucoma, cataracts and other events.
Diagnostic tests for juvenile idiopathic arthritis
The US National Library of Medicine shows us, in detail, how doctors diagnose juvenile idiopathic arthritis. First, the physical examination can give some clues, since the patient usually shows swollen, hot, reddened and painful joints to the touch.
In any case, each type of JIA is different. As we have seen, the psoriatic variant presents with skin peeling and the systemic one with swollen lymph nodes. Therefore, many tests are usually necessary, among which we highlight the following:
- Blood tests: here circulating rheumatoid factor (RF) is detected in the blood, if present. The erythrocyte sedimentation rate (ESR), the presence of antinuclear antibodies (ANA) are also quantified and used to make a complete blood count.
- X-ray: to quantify the damage and condition of the affected joints.
- Regular eye exams: Since uveitis affects up to 30% of children with JIA, they should go to the ophthalmologist regularly.
- MRIs and other imaging tests: These are done to rule out fractures and superficial injuries.
Beyond all these tests, the professionals will follow the same classification criteria that we have previously exposed to diagnose the specific type of JIA. If the patient shows signs of several of the categories, he is considered to have undifferentiated juvenile idiopathic arthritis.
Possible Treatments for Juvenile Idiopathic Arthritis
As indicated by the aforementioned portals, juvenile idiopathic arthritis requires a multidisciplinary approach that is responsible for managing both the pain of the disease and the possible psychological effects and pathologies that derive from it. Below we show you the treatment on 2 different fronts, but complementary.
1. Pharmacological treatment
Non-steroidal anti-inflammatory drugs (NSAIDs) are the long-term treatment of all forms of JIA. In any case, it is recommended to change the strategy if the arthritis is still as active after 2 months of the start of the plan. Only a few NSAIDs are approved for children: naproxen and ibuprofen are the most common.
On the other hand, intra-articular corticosteroid injections are widely used in children with JIA, especially those with oligoarthritis. Oral systemic corticosteroids may also be prescribed, but only in cases where there are symptoms beyond the affected joint areas.
Finally, the antirheumatic drug methotrexate (MTX) is another of the drugs of choice for some types of cancer and autoimmune diseases, such as rheumatoid arthritis and JIA. It is prescribed in doses of 10 milligrams per square meter of the body, once a week, orally.
2. Non-pharmacological treatment
In non-pharmacological treatment we find changes in lifestyle and seeking help from other professionals. For example, a visit to the physical therapist can help the child maintain muscle tone and range of motion. On the other hand, psychotherapy is useful for managing the pain and discomfort of a chronic condition.
There is no single disease in juvenile idiopathic arthritis
Juvenile idiopathic arthritis does not refer to a single disease, but to a group of pathologies that joint pain in children under 16 years of age has in common, with or without other symptoms. Each variant carries different discomforts and risks. Therefore, they must be treated autonomously.
Unfortunately, this condition has no cure. Exercising, leading a healthy lifestyle and not neglecting the body will always help children to cope with the disease correctly, especially if the doctors give the appropriate treatment.
