Adult-onset Still’s disease (AOSD) is a rare condition that is estimated to cause up to 0.4 cases in every 100,000 adults.

There’s also a version that affects children called systemic onset juvenile inflammatory arthritis (SoJIA).

AOSD is an inflammatory condition that can cause exhaustion and swelling in your joints, tissues, organs, and lymph nodes.

The most common symptoms of AOSD include:

This condition goes through episodes of flare-up and remission: Symptoms can appear and disappear suddenly. They also sometimes never come back.

Some people with AOSD may only ever experience one flare-up. Others may have another episode happen again years later, or they may experience multiple episodes in a few months.

The most common AOSD symptom is a fever that lasts for several days and peaks (spikes) at the same time each day. For some, the fever may spike twice a day, at the same times each day.

You may also notice a quick-changing rash on your skin that may look similar to hives. Unlike hives, this rash isn’t itchy.

Other symptoms of AOSD include:

In rare cases, the liver or spleen can become enlarged. The tissues around major organs like the heart and lungs may also become inflamed.

A rare complication of AOSD is macrophage activation syndrome (MAS), which can result in serious, sometimes life threatening, inflammation in the body.

According to Mayo Clinic, people between 15 to 25 years and 36 to 46 years are at a higher risk for AOSD. Men and women are affected by this condition at about the same rate.

The causes of adult Still’s disease are still unknown. The condition may be related to certain antigens.

Antigens are substances that can cause your body to mount an immune response, activate immune system cells, and produce antibodies. This immune response can aid in fighting infection or result in body-wide inflammation.

You doctor may recommend multiple tests to make sure that a diagnosis of AOSD is correct.

Certain types of cancer, mononucleosis, and conditions like Lyme disease share many initial symptoms with Still’s disease and need to be ruled out before a diagnosis can be confirmed.

Your doctor may also order a blood test to check your level of ferritin, which is often in high levels in people who have AOSD.

The three initial symptoms that could indicate AOSD include:

  • fever
  • rash
  • joint pain

Your doctor will follow up with additional blood test results to learn more about your joint inflammation and to help you develop a treatment plan.

Your doctor will also listen to your heart and lungs and may use radiology tests to examine your chest, liver, and spleen.

If you’re experiencing severe symptoms, your doctor may order a bone marrow biopsy to check for MAS.

The earliest symptoms of AOSD are often followed by the development of arthritis.

This means that your doctor will usually focus treatment on the symptoms and effects of arthritis. The most common treatment is a short course of prednisone.

Side effects of prednisone can include high blood pressure and fluid retention, so your doctor may limit how much they prescribe you to take.

Milder cases may only need treatment with nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil).

If your AOSD becomes chronic, your doctor may prescribe medications that modulate your immune system, including:

These medications are also used to treat inflammatory arthritis, such as rheumatoid arthritis, because they reduce how many corticosteroid injections you need, and specifically target immune response pathways.

You’ll need to take your prescribed medications for AOSD consistently for the best results.

Light, regular exercise can also help maintain your muscle and joint strength. Your doctor or a physical therapist can help suggest a general exercise plan for you.

Your doctor or a nutritionist may recommend vitamin supplements, such as calcium and vitamin D, to help prevent osteoporosis, especially if you’re taking prednisone.

There’s currently no cure for AOSD. But it can be treated, and regular treatment can help manage your symptoms if they happen again.

A small number of people with AOSD will develop chronic arthritis with joint symptoms that persist for years. But medications and self-care can help.

Talk with your doctor about how best to treat and manage your specific AOSD symptoms.