Adult-onset Still's disease

Adult-onset Still's disease is an autoinflammatory condition: rather than the body attacking one specific target, parts of the innate immune system switch on inappropriately and flood the body with inflammatory signals, particularly interleukin-1 and interleukin-6. This drives the spiking fevers, rash and joint inflammation.

The trigger is not known. An infection or other stress may set off the immune response in someone who is predisposed, but no single cause has been identified, and it is not inherited or contagious.

It is rare and can affect anyone, though it is seen most often in younger and middle-aged adults, with a roughly equal split between men and women. It is closely related to systemic juvenile arthritis seen in children.

Adult-onset Still's disease has a fairly characteristic pattern. Features may include:

• High fevers, often spiking once or twice a day
• A salmon-pink rash that may appear and fade with the fevers
• Joint pain and swelling, and muscle aches
• Chest pain, if the thin linings around the heart or lungs become inflamed
• A sore throat, and sometimes a general sense of being unwell

Adult-onset Still's disease can also inflame the thin linings around the heart and lungs, causing pericarditis and pleurisy. Doctors group these under the term serositis, and it is a recognised feature of the condition. The pain is usually sharp rather than crushing, tends to be worse when you breathe in or lie down, and often eases when you sit up and lean forward. It generally settles as the disease itself is brought under control. Even so, chest pain is never something to diagnose yourself: any new chest pain needs prompt assessment, and in adult-onset Still's disease chest pain and breathlessness can also be warning signs of macrophage activation syndrome, the rare complication described later in this guide. There is more about how inflammation can affect the heart in our guide to inflammation and your heart.

There is no single test for adult-onset Still's disease. The diagnosis is made from the characteristic combination of features, supported by blood tests that often show marked inflammation, and importantly by excluding infections, other inflammatory conditions and other causes of fever. This makes thorough specialist assessment essential.

Where joints are involved, ultrasound can help assess inflammation. Dr Borukhson uses point-of-care ultrasound during the consultation. You can read more on the ultrasound clinic page.

Treatment aims to bring the inflammation under control, settle the fevers and joint symptoms, and prevent flares. Corticosteroids such as prednisolone are often used to settle active disease, and a medicine such as methotrexate may be added to keep the inflammation controlled while the steroid dose is reduced. For persistent or severe disease, biological medicines that block particular inflammatory signals, for example anakinra (which blocks IL-1) or tocilizumab (which blocks IL-6), can be very effective.

These treatments need monitoring while you are taking them, and biological medicines can increase the risk of infection, so they are used under specialist supervision and discussed fully with you. Treatment is individual and kept under careful review, and because the condition can fluctuate, ongoing specialist input is valuable. The plan is agreed with you.

In a small number of people, adult-onset Still's disease can trigger an extreme overactivation of the immune system known as macrophage activation syndrome (MAS), a form of haemophagocytic lymphohistiocytosis (HLH). It is uncommon, but it is a life-threatening medical emergency that can develop as the disease first appears or during a severe flare, and it needs immediate hospital treatment. This is one of the reasons close specialist monitoring is so important.

Seek urgent medical help if you become rapidly unwell with a persistent high fever that will not settle, easy bruising or bleeding, yellowing of the skin or eyes, or new confusion or drowsiness. These can be warning signs of this complication and need emergency assessment without delay. Call 999 or attend A&E.

Day to day, the most useful thing you can do is keep your specialist team informed and attend your review appointments and blood tests, as these check both the disease and your medication. Keeping a simple note of any fevers, rashes or joint flares to bring along helps tailor treatment.

• Pace yourself during flares and rest when feverish, then rebuild gentle activity as things settle
• Look after your bones with weight-bearing exercise, and ask about calcium and vitamin D if you are on steroids
• Keep vaccinations up to date, and discuss any planned pregnancy or new medicine first

The outlook is generally good. Some people have a single episode that resolves, while others have a relapsing or longer-term course, so it is kept under ongoing review.

Seek emergency help, by calling 999 or attending A&E, if you develop a persistent very high fever that will not settle, easy bruising or bleeding, yellowing of the skin or eyes, breathlessness, chest pain, or new confusion or drowsiness. These can signal macrophage activation syndrome, a rare but life-threatening complication.

Contact your GP or specialist team urgently, the same day, if you feel rapidly more unwell, a flare is not responding to your usual treatment, or you develop signs of infection such as a fever while on steroids or a biological medicine, as these treatments can mask or worsen infection.

Arrange a routine review for gradually returning joint pain, swelling or recurring low-grade fevers, so treatment can be adjusted before a full flare takes hold.

The combination of persistent high fevers, rash and joint pain always needs proper assessment, both to reach the right diagnosis and to exclude other serious causes. If you have these symptoms, a prompt specialist review is important.

How is adult-onset Still's disease diagnosed?

There is no single test that confirms it. The diagnosis rests on the characteristic pattern of high spiking fevers, a salmon-coloured rash and joint symptoms, supported by blood tests that usually show marked inflammation, and importantly by ruling out infections and other conditions that can mimic it. This careful process takes specialist assessment. Where joints are involved, Dr Borukhson can use point-of-care ultrasound during the consultation to look for inflammation.

How is it treated, and will it ever settle?

Treatment aims to calm the inflammation, settle the fevers and joint symptoms, and prevent flares. Steroids such as prednisolone often bring active disease under control quickly, with a medicine like methotrexate added to maintain control as the steroid is reduced. For persistent or severe disease, biological treatments that block specific inflammatory signals can be very effective. Many people improve well, though the condition can fluctuate, so it is kept under careful review.

How is adult-onset Still's disease different from rheumatoid arthritis?

Both are inflammatory conditions affecting the joints, but the pattern differs. Adult-onset Still's disease typically causes high spiking fevers, a fleeting salmon-coloured rash and a sore throat alongside the joint pain, whereas rheumatoid arthritis is centred on persistent joint inflammation without those daily fevers and rash. The two are also distinguished by blood tests and by excluding other causes, which is part of why specialist assessment matters.

Can adult-onset Still's disease affect the heart or lungs?

Yes. It can inflame the thin linings around the heart (pericarditis) and lungs (pleurisy), which doctors group together under the term serositis, a recognised feature of the condition. The chest pain is typically sharp rather than crushing, worse on breathing in or lying down, and eased by sitting up and leaning forward, and it usually settles as the underlying inflammation is treated. Any new chest pain needs prompt medical assessment. In adult-onset Still's disease, chest pain and breathlessness can also be warning signs of macrophage activation syndrome, so do not wait to have them checked.

When should I seek urgent medical help?

Seek urgent help if you become rapidly unwell with a persistent high fever that will not settle, easy bruising or bleeding, yellowing of the skin or eyes, or new confusion or drowsiness. These can be warning signs of a rare but serious complication called macrophage activation syndrome, which needs emergency assessment. Call 999 or attend A&E. Close specialist monitoring helps catch problems early.

Do I need to see a specialist?

Yes. The combination of persistent fevers, rash and joint pain always needs proper assessment, both to reach the right diagnosis and to exclude other serious causes. Because there is no single confirmatory test and the condition can fluctuate and occasionally cause complications, ongoing specialist input is valuable. A prompt review allows the cause to be established and the right treatment, tailored to you and kept under careful review, to begin.