Juvenile idiopathic arthritis is a common type of arthritis that affects children; it is earlier known as juvenile rheumatoid arthritis. Children under 16 years of age are mostly affected.
It is a chronic disease that affects any joint of the body. The immune system mistakenly targets synovium (synovium is a tissue that lines the inside of the joint). The synovium responds by making excess synovial fluid which leads to persistent joint pain, swelling, and stiffness. The inflammation and synovium spreads to the surrounding tissues and damage cartilage and bone.

Some children may see the early symptoms only for a few months, while others have symptoms lifelong. Some categories of juvenile idiopathic arthritis can give rise to critical problems, such as growth and development problems, joint damage, and eye inflammation. Treatment is given to reduce pain and inflammation, improving the function of the joints, and preventing any further joint damage.

There are many types of Juvenile idiopathic arthritis they are: - Systemic arthritis, Oligoarthritis, Polyarthritis, Psoriatic arthritis, Enthesitis-related arthritis.

Symptoms of JIA:
Depends on the type of JIA, the symptoms vary. Common symptoms are

Morning stiffness: you might have noticed that your child is unable to walk especially in the morning.
Pain: the child appears clumsier than usual mainly in the mornings and after taking nap.
Swelling and tenderness in the joints: it is mostly noticed in the larger joints such as knee.
Limping, fever, rash, weight loss, fatigue, eye redness, and blurred vision: these symptoms usually worsen in the evenings.
Based on the symptoms and the number of joints affected the type of disease is identified.
Symptoms come and go over days or weeks. When the child has less fever it seems to be fine. When it flares up, the child will feel sick. Children will have good days with very few or without any symptoms, and worse days with flare up symptoms.This condition might cause inflammation in the lining of the lung (pleuritis) or heart (pericarditis). It may also cause swollen lymph nodes. Children with these conditions may grow slowly than normal.

Causes:
Juvenile idiopathic arthritis occurs when our own body's immune system attacks its own cells and tissues. Research indicates that it is an autoimmune disease. White blood cells can’t tell the difference between healthy cells and germs. Instead of protecting from these harmful invaders, it damages healthy tissues and cause inflammation and pain. It's unknown why this happens, but both heredity and environment seem to play a vital role in causing the disease. Certain gene mutations may make a person more vulnerable to environmental factors like viruses that are the triggering source of the disease.