Systemic juvenile idiopathic arthritis (SJIA) is a rare autoinflammatory disease, affecting only 10% to 15% of children with juvenile idiopathic arthritis (JIA). Formerly called "Still's disease," SJIA is considered to be a type of JIA, but the symptoms, underlying cause and treatments for it are all different. In children with SJIA, the innate immune system (the part of the immune system you are born with) is overactive. This leads to inflammation in the joints and in other parts of the body. The cause of this overactivity is not fully understood, but it is probably due to a combination of genetic and environmental factors.

Although it most commonly affects young children, the symptoms may start at any age. The adult form of SJIA is known as adult-onset Still's disease (AOSD), and this is also a very rare disorder.

Symptoms of SJIA

The following symptoms may occur all at once, or spread out over several days or weeks. Children with SJIA have fevers, rashes and arthritis.

• The arthritis symptoms can include swelling, warmth and pain in the joints.
• The fevers typically occur once daily around the same time every day. This can make the disease hard to diagnose, as children may look very ill when they have the fever but then totally normal when the fever goes away.
• The rash is flat and pink in color, and it may be visible only when the fever is present.
• Other symptoms may include swollen lymph nodes and inflammation of internal organs – such as the liver, spleen and the lining of the heart (pericarditis) or lung (pleuritis).

Diagnosis and treatment

There are no specific medical tests for SJIA. A doctor will typically make a diagnosis based on:

• The collection of symptoms your child has
• Clinical findings
• Laboratory tests (blood work usually shows signs of inflammation, and helps to rule out an infectious cause)
• Imaging of the heart or lungs (echocardiogram, chest X-ray, chest CT scan)
• (In rare cases, when the diagnosis is unclear) a skin biopsy, which may help the physician better evaluate the rash.

Your child’s rheumatologist may recommend an exam by an ophthalmologist to evaluate for ocular inflammation (uveitis), although this is less common than in the other types of JIA.

The goal of treatment is to reduce the symptoms and treat the underlying inflammation. Many children require corticosteroids, as well as other immunosuppressive medications. Biologic medications that target specific inflammatory molecules (interleukins), such as anakinra, canakinumab and tocilizumab, may help treat both the systemic inflammation and the arthritis. These medications are given by injection or IV infusion.