Juvenile idiopathic arthritis, a type of arthritis that develops in children, is composed of six individual subtypes that are each unique in their own characteristics. These subtypes are systemic, oligoarticular, polyarticular, juvenile psoriatic, enthesitis-related and undifferentiated arthritis.
The common symptoms that are present across each individual subtype of juvenile idiopathic arthritis are the same symptoms that characterize every subtype of arthritis – pain, swelling and inflammation of joints.
Each subtype is unique with regards to the location of joint affected, the combination of joints that are affected, the number of joints that are affected, the symptoms that the patients display and the organ systems involved. In fact, while some forms of Juvenile idiopathic arthritis involve the musculoskeletal system, others can involve organs such as the eyes, skin and gastrointestinal tract. Below you will find listed six subtypes of juvenile idiopathic arthritis
1. Systemic juvenile idiopathic arthritis, also known as Still’s disease
This type of arthritis develops equally in boys and girls. Approximately 10% of all patients with juvenile idiopathic arthritis have a systemic-onset, which means that the inflammation is not just restricted to joints but also extends to the spleen, liver, and the membrane that covers the heart. Due to the systemic nature of this disease, patients might start experiencing symptoms in other parts of the body before they experience any joints problems. Hence, symptoms can be confusing, which can lead to a delay in diagnosis of the disease. Unfortunately, the systemic-onset subtype is quite severe in its symptoms and patients experience a range of symptoms such as:
- High fever
- Skin rash, generally on the legs, trunk and arms
- Enlarged glands, which can manifest in the neck, underarms, and groin.
- Loss of appetite and weight loss
- Fatigue and weakness
2. Oligoarticular juvenile idiopathic arthritis
Oligoarticular arthritis is the most common subtype of juvenile idiopathic arthritis and comprises about 66% of all juvenile idiopathic arthritis cases. Interestingly, it is much more frequently diagnosed in males compared to females, though the boys will likely outgrow the disease by the time they are adults. Unlike systemic juvenile idiopathic arthritis, symptoms associated with oligoarthritis are much less severe and are not associated with any permanent joint damage. The joints that are most frequently affected include larger ones such as knees and elbows. These are the symptoms that are seen in patients with oligoarticular juvenile idiopathic arthritis:
Joint pain and inflammation that involves less than 5 joints in the first 6 months. If the child later develops involvement of more than 4 joints, then the disease is classified as extended oligoarticular juvenile idiopathic arthritis .
Chronic anterior uveitis (eye inflammation)
This complication can eventually lead to compromised vision if it is not promptly treated. However, patients with uveitis often feel no pain and have no eye redness, so it can be a hard complication to diagnose. Therefore, regular eye checkups are necessary.
3. Polyarticular juvenile idiopathic arthritis
This subtype of arthritis is also common and makes up around 25% of all patients with juvenile idiopathic arthritis. Polyarticular juvenile idiopathic arthritis is more frequently diagnosed in girls than boys. Patients with this subtype tend to progress quickly, often in a matter of months. The symptoms appear suddenly and involve multiple joints (five or more) in the first six months. The joints that are involved in polyarticular juvenile idiopathic arthritis generally include smaller ones such as those present in the toes or fingers. The disease can often progress to involve other, larger joints such as ankles, hips, knees and jaw. Other symptoms of polyarticular juvenile idiopathic arthritis include:
4. Juvenile psoriatic arthritis
Juvenile psoriatic arthritis develops in children that have a skin disease known as psoriasis. Hence, patients with juvenile psoriatic arthritis have both arthritis and psoriasis, either of which can develop first. These are symptoms associated with this subtype:
- Scaly, red rash, often on eyelids, back, knees, butt, or scalp. The rash can also appear behind the ears.
- Pitted (discoloration and thickening of) fingernails
5. Enthesitis-related arthritis, also known and spondyloarthritis
This subtype of arthritis affects and causes inflammation of the entheses, which refers to the region where tendons meet bones. It can also affect the spine, hips and eyes. It is much more frequently diagnosed in boys, specifically those that are older than eight. One of the causes of enthesitis-related arthritis is thought to genetics, as there is often a family history of the disease in male relatives. These are the symptoms that can develop in people with enthesitis-related arthritis:
- Stiffness of lower back and neck
- Acute uveitis
6. Undifferentiated arthritis
This subtype of arthritis is for children that demonstrate symptoms of arthritis that are inconsistent with any of the other five known subgroups. Children that display symptoms that go across subgroups can also be put into this category. Essentially, if your child has arthritis but the doctor can’t figure out which category he or she belongs in or has a mixture of these categories, then they are diagnosed with undifferentiated arthritis.