What Is the Difference Between Still’s Disease, Juvenile Idiopathic Arthritis, and Rheumatoid Arthritis?

Adult-onset Still’s disease (AOSD), systemic juvenile idiopathic arthritis (SJIA), and rheumatoid arthritis (RA) are all forms of arthritis that share many similar features. It can be hard to tell them apart. However, there are several differences between them that can help with diagnosis and treatment.

AOSD is the adult form of SJIA

SJIA is also called Still’s disease. It is diagnosed in kids younger than 16 years old. This is the main difference between it and AOSD, which is diagnosed in people over age 16. There are several different types of juvenile idiopathic arthritis (JIA) that kids can get. SJIA makes up about 1 in 10 cases of JIA.^1-3

The most common symptoms of AOSD and SJIA are the same, including:^1,2

• Fever
• Rash
• Joint pain
• Swollen lymph nodes

Both SJIA and AOSD are caused by an overactive immune system. Specifically, the body has higher-than-normal levels of inflammatory cytokines. These are proteins that act all over the body to cause inflammation.^1,3

This inflammation most commonly damages the joints. However, other complications are possible with AOSD and SJIA too. One potentially life-threatening issue that can occur with both conditions is called macrophage activation syndrome (MAS).^1-3

Diagnosing and treating AOSD and SJIA

SJIA and AOSD are diagnosed in generally the same way. Blood tests that look for inflammation and help rule out other similar health conditions are the main method of diagnosis. Treatment of SJIA and AOSD are roughly the same, too, and include drugs that help reduce inflammation.^1-3

However, there are some special considerations that need to be made when treating SJIA in kids. Some drugs used to treat AOSD, like certain biologic drugs, may not be approved for use with kids. This means that research has not shown that they are safe for kids to take.^1,2

Also, some common treatment options can have a greater long-term effect on kids than on adults. An example is steroids. Steroids can have more risks for kids because they are still growing. Their use in children may need to be limited more than it is in adults.^1,2

Differences between AOSD and RA

AOSD and RA are both types of inflammatory arthritis. However, the way this inflammation occurs differs between the 2.^2-4

A person with AOSD has overactive cytokines that cause general immune system issues. Cytokines are part of the innate immune system. The innate immune system is your body’s first line of defense against germs. Common signs that your innate immune system is working include fever, muscle aches, and general rash. These also all can be signs of AOSD.^3,4

On the other hand, RA is related to the adaptive immune system. The adaptive immune system is more specialized than the innate immune system. It can target specific germs to keep you healthy. The adaptive immune system plays a role in making antibodies. These are proteins that have unique targets in the body. In people with RA, the body makes antibodies that mistakenly attack healthy cells.⁵

Symptom differences

A health condition that affects the innate immune system, like AOSD, is sometimes called an autoinflammatory condition. Issues that affect the adaptive immune system, like RA, are called autoimmune conditions.^3,4

This difference can help explain some of the symptoms of each type of arthritis. Since it is a more general immune response, AOSD has symptoms like fever or rash before joint pain starts. People with AOSD also often have swollen lymph nodes, an early sign of the immune system ramping up.²

On the other hand, people with RA are less likely to have the recurring fevers of AOSD. Instead, their early symptoms often are limited to the joints. People with RA may have one or more joints that are stiff in the morning and get worse over time. The joints most commonly affected first are in the hands. But AOSD often impacts the wrists and knees early on.^2,5

Diagnosis and treatment differences

Like with SJIA, the process of diagnosing AOSD and RA is similar. Many of the same tests are used. Often, doctors will try to rule out RA when diagnosing AOSD.²

One difference that doctors look for during diagnosis is found in blood test results. People with RA often have specific markers in the blood that are less common in those with AOSD. These include markers called rheumatoid factor (RF) and anti-CCP.²

Treating both conditions follows a similar overall plan too. The ultimate goals are to reduce inflammation and slow joint damage. Some treatment options are used for both, including:^5-7

• Non-steroidal anti-inflammatory drugs (NSAIDs)
• Steroids
• Disease-modifying antirheumatic drugs (DMARDs)

However, targeted treatments for AOSD often focus on reducing the effects of certain cytokines. On the other hand, targeted RA treatments may aim to reduce the production of antibodies or other aspects of the adaptive immune system.^5-7