Adult-Onset Still’s Disease: Fevers, Rash, Joint Pain and Why Diagnosis Can Be Difficult
Adult-onset Still’s disease is a rare inflammatory condition that can cause high fevers, rashes, joint pain and inflammation affecting several parts of the body. It can begin suddenly and make someone extremely unwell, yet the diagnosis is often difficult to establish.
The difficulty is not simply that the disease is rare. Its early features can resemble infection, lymphoma, leukaemia, other autoimmune diseases and adverse drug reactions. There is also no single blood test that confirms the diagnosis.
A raised ferritin can be an important clue, sometimes dramatically so, but ferritin is not specific to Still’s disease. Diagnosis requires the pattern of symptoms, examination and investigations to fit together—and other serious causes of systemic inflammation to be considered carefully.
What is adult-onset Still’s disease?
Adult-onset Still’s disease, usually abbreviated to AOSD, is a systemic autoinflammatory disease. “Systemic” means that it can affect the whole body rather than only the joints.
Autoinflammatory diseases arise predominantly from inappropriate activation of the innate immune system—the body’s rapid first-line inflammatory response. This differs somewhat from classic autoimmune diseases, in which antibodies and immune cells target particular tissues. In practice, the distinction is not absolute, but it helps explain why Still’s disease often presents with dramatic fever and inflammation.
The cause is not fully understood. Infections may sometimes act as triggers, but Still’s disease is not itself an infection and is not contagious.
How is adult-onset Still’s disease related to systemic JIA?
Systemic juvenile idiopathic arthritis, or sJIA, is the childhood-onset form of Still’s disease. It was historically treated as a separate condition, but current understanding is that sJIA and adult-onset Still’s disease form a continuum of the same systemic autoinflammatory disease.
The distinction is based principally on age at onset. In UK guidance, disease beginning at or before the age of 16 is generally classified as sJIA, while onset after 16 is described as adult-onset Still’s disease. Someone whose illness began in childhood continues to have sJIA when they move into adult rheumatology care; the diagnosis does not change simply because they become an adult.
The two conditions share important features, including spiking fever, rash, arthritis, raised inflammatory markers and the risk of macrophage activation syndrome. Treatment principles increasingly overlap, particularly the early use of medicines targeting IL-1 or IL-6.
However, the pattern of illness, treatment licences and NHS access arrangements can differ between children and adults. This makes well-planned transition from paediatric to adult rheumatology important for young people with ongoing Still’s disease.
The characteristic pattern
The classic presentation combines four features:
high, spiking fevers
a transient rash
joint pain or arthritis
markedly raised inflammatory markers
However, not everyone develops all four features at the same time. Arthritis may appear after the fever has begun, while the rash may be brief and difficult to see. This is one reason that requiring a perfect textbook presentation can delay diagnosis.
Spiking fever
The fever of Still’s disease is often high, sometimes reaching 39°C or above. It may rise rapidly once or twice each day and then fall towards normal between episodes.
Some people feel relatively better when the temperature falls and profoundly unwell during the next spike. Others develop a more persistent fever, particularly when the disease is severe or complicated.
The timing can be diagnostically useful, but no fever pattern is exclusive to Still’s disease. Infection and malignancy must remain part of the assessment.
The Still’s disease rash
The classic rash is described as evanescent, meaning that it appears and fades. It is often salmon-pink and may emerge during a fever spike, affecting the trunk, arms or legs.
In reality, the rash is not always textbook in appearance. It may be faint, difficult to appreciate on some skin tones, mildly itchy or more persistent than expected. Patients may notice it only after a hot shower, physical activity or a rise in temperature.
Photographs taken when the rash is visible can therefore be valuable. Occasionally, dermatological assessment and a skin biopsy are helpful, particularly when the appearance is atypical.
Joint and muscle symptoms
Joint pain is extremely common, but objective arthritis does not necessarily occur at the beginning. This matters because the absence of swollen joints during the first assessment should not automatically exclude Still’s disease.
When arthritis develops, it may affect the wrists, knees, ankles, elbows, shoulders or the small joints of the hands. Some patients experience an acute inflammatory illness dominated by fever, while others develop persistent arthritis that becomes the main long-term problem.
Severe muscle aching can also occur during fever spikes. This must be distinguished from genuine muscle weakness, which may suggest an inflammatory muscle disease or another diagnosis.
Sore throat
A severe sore throat is a surprisingly characteristic early feature. It may precede the fever or accompany the first systemic flare.
Throat examination and infection tests may be unrevealing. Because sore throat and fever naturally suggest infection, this feature can initially direct the assessment away from rheumatology.
Still’s disease can affect more than the joints
Still’s disease may cause enlarged lymph nodes, enlargement of the liver or spleen and abnormal liver tests. Inflammation can also affect the lining around the lungs or heart, causing pleurisy, pleural fluid or pericarditis.
Chest pain that becomes worse on breathing or lying flat, unexplained breathlessness and a persistent cough require prompt assessment. Lung involvement is uncommon but potentially serious.
Other possible features include abdominal pain, weight loss, profound fatigue and a general sense of being acutely unwell.
Why diagnosis can take time
Adult-onset Still’s disease is diagnosed from a combination of positive clinical features and the careful exclusion of alternatives.
Early in the illness, the most urgent question is often whether the patient has an infection. Blood cultures, viral tests and imaging may be required depending on the presentation. Starting immunosuppressive treatment before a serious infection has been considered can be dangerous.
Malignancy—particularly lymphoma and leukaemia—can also cause fever, weight loss, enlarged lymph nodes, abnormal blood counts and a raised ferritin.
Other possible mimics include lupus, vasculitis, inflammatory muscle disease, periodic fever syndromes, inflammatory bowel disease and severe drug reactions.
This does not mean that every patient requires every possible test. Investigation should be guided by the clinical pattern. But the diagnosis should not be based on fever and a high ferritin alone.
What do the blood tests show?
There is no single diagnostic test for adult-onset Still’s disease.
Common findings include:
a raised white-cell count, often with increased neutrophils
high CRP and ESR levels
raised ferritin
abnormal liver enzymes
anaemia and raised platelet numbers during active inflammation
negative rheumatoid factor and antinuclear antibody tests
These findings support an inflammatory pattern, but none is specific. Rheumatoid factor and ANA are often negative, although an incidental positive result does not make Still’s disease impossible.
Blood counts can also change as the illness evolves. A high white-cell and platelet count may accompany uncomplicated active disease, while falling cell counts can be a warning sign of macrophage activation syndrome.
Ferritin: an important clue, but not a diagnosis
Ferritin is best known as a marker of the body’s iron stores, but it also rises during inflammation.
In Still’s disease, ferritin may be markedly or even extraordinarily elevated. A very high result in someone with fever, rash, joint symptoms and neutrophilia should raise suspicion. The trend can also be helpful: a rapidly rising ferritin may indicate escalating systemic inflammation.
However, ferritin can also rise substantially in severe infection, liver injury, malignancy and macrophage activation syndrome. Some patients with Still’s disease have only a moderate elevation, particularly early in the illness.
Specialist tests such as glycosylated ferritin, interleukin-18 or S100 proteins may provide additional support in selected centres, but they are not universally available and do not replace clinical assessment.
Are diagnostic criteria used?
Classification systems such as the Yamaguchi and Fautrel criteria can help organise the clinical picture. They consider combinations of fever, joint symptoms, rash, white-cell abnormalities and other findings.
These criteria are useful, particularly once important alternative diagnoses have been assessed, but they are not a substitute for clinical judgement. Classification criteria were principally designed to identify reasonably consistent groups for research; they should not be treated as a stand-alone diagnostic test.
A patient can have convincing evolving Still’s disease before every criterion is present. Conversely, someone may technically meet several criteria while actually having an infection or malignancy.
The different patterns of disease
Several patterns have traditionally been described.
Some people experience a single inflammatory episode followed by lasting remission. Others have recurrent flares separated by periods of good health. A third group develops persistent disease, often with chronic arthritis.
These patterns are useful descriptions, but they cannot always be predicted at the beginning. The course can also change, particularly now that effective targeted treatments are available.
The practical aim is to control inflammation promptly, minimise exposure to corticosteroids, monitor for complications and work towards remission.
How is adult-onset Still’s disease treated?
Treatment depends on the severity of the illness, the organs involved and whether fever, systemic inflammation or arthritis predominates.
NSAIDs may provide temporary relief from fever, joint pain and stiffness while investigations are taking place. They are rarely sufficient for established, active systemic disease and should not delay more effective treatment when someone is significantly unwell.
Corticosteroids can suppress inflammation rapidly and remain important for severe presentations, including pericarditis, major systemic inflammation and impending macrophage activation syndrome.
The problem is that prolonged or repeated high-dose steroid treatment can lead to infection, osteoporosis, diabetes, weight gain, hypertension and other complications. Modern treatment therefore aims to control the disease without long-term dependence on corticosteroids.
IL-1 and IL-6 inhibitors
Two inflammatory signalling pathways—interleukin-1 and interleukin-6—are particularly important in Still’s disease.
Anakinra blocks the IL-1 receptor. Canakinumab is another IL-1-targeted treatment, while tocilizumab blocks the IL-6 receptor. These treatments can improve fever, rash, inflammatory markers and arthritis, although the most appropriate choice depends on the clinical presentation and individual circumstances.
Current EULAR and PReS recommendations prioritise IL-1 or IL-6 inhibitors and advise starting one early once the diagnosis has been established. This represents an important shift away from prolonged treatment with corticosteroids and repeated trials of less targeted medication.
In UK practice, access is also influenced by licensing, NICE recommendations and NHS commissioning criteria. Anakinra is licensed for active Still’s disease and is recommended by NICE for specified patients with adult-onset disease. Tocilizumab is available through NHS England commissioning criteria for selected refractory cases.
Methotrexate and other conventional treatments
Methotrexate has traditionally been used as a steroid-sparing treatment, particularly when persistent arthritis is prominent. It may still be appropriate for some patients, including where access to targeted treatment is limited or where the joint pattern supports its use.
However, evidence for conventional DMARDs in the systemic features of Still’s disease is limited. International recommendations now place greater emphasis on IL-1 and IL-6 inhibition.
Treatment should be reviewed against clear targets rather than continued indefinitely without knowing whether it is working.
Macrophage activation syndrome: the complication that must not be missed
Macrophage activation syndrome, or MAS, is a severe and potentially life-threatening escalation of inflammation. It belongs to the spectrum of haemophagocytic lymphohistiocytosis, often abbreviated to HLH.
MAS may occur when Still’s disease first presents, during a later flare or occasionally after a triggering infection. It can evolve rapidly.
Warning features include persistent rather than intermittent fever, a rapidly rising ferritin, falling platelet or white-cell counts, worsening liver tests, abnormal blood clotting, rising triglycerides, enlargement of the liver or spleen and deterioration in organ function.
These findings can be counterintuitive. Active uncomplicated Still’s disease commonly produces a high white-cell count and raised platelets. If those counts begin to fall while the patient becomes more unwell, this should not automatically be interpreted as improving inflammation.
MAS requires urgent specialist and frequently hospital-based treatment. High-dose corticosteroids are central to treatment, often combined with therapies such as anakinra or ciclosporin according to the clinical situation. Possible triggers, particularly infection, must be sought and treated at the same time.
A patient with Still’s disease who develops persistent high fever, confusion, unusual bruising or bleeding, severe breathlessness, chest pain or rapid clinical deterioration should seek urgent medical assessment.
Monitoring treatment
Monitoring involves more than checking the CRP.
Symptoms, fever pattern, joint examination, blood counts, ferritin, liver tests and treatment toxicity all need to be considered. Imaging or organ-specific assessment may be required when there is chest pain, breathlessness, persistent cough or other evidence of internal-organ involvement.
This is especially important during treatment with an IL-6 inhibitor such as tocilizumab, because blocking IL-6 can substantially suppress CRP. A low CRP in that setting should not override concerning clinical features.
Monitoring should also address the effects of treatment, including infection risk, vaccination, bone protection during corticosteroid use and the laboratory monitoring required for biologic or conventional DMARD therapy.
Can Still’s disease go into remission?
Yes. Some people experience one episode and never relapse. Others achieve remission with treatment, while a proportion have recurrent or persistent disease.
The outlook has changed significantly with the introduction of IL-1 and IL-6 inhibitors. Current treatment strategies aim for clinically inactive disease without corticosteroids and, ultimately, sustained remission with the possibility of carefully reducing treatment.
Medication should not be stopped suddenly simply because symptoms and blood tests have improved. Remission needs to be sustained, and any reduction should be planned with the treating rheumatology team.
When a second opinion may help
A specialist review can be valuable when someone has unexplained recurrent fevers, rash, joint symptoms and persistently raised inflammatory markers—particularly when ferritin is elevated and investigations for infection have not provided an explanation.
A second opinion may also help when:
the diagnosis remains uncertain
the symptoms do not fit the proposed diagnosis
ferritin results are being interpreted in isolation
corticosteroids cannot be reduced without relapse
systemic inflammation remains active despite treatment
macrophage activation syndrome has occurred or is suspected
targeted treatment options need to be considered
The purpose is not simply to apply diagnostic criteria. It is to reconstruct the timeline, review the fever and rash pattern, examine for arthritis or organ involvement, reconsider important mimics and decide what further assessment or treatment is justified.
The bottom line
Adult-onset Still’s disease is a rare systemic autoinflammatory condition that can cause high fevers, a transient rash, joint pain or arthritis, sore throat and marked inflammation.
Systemic juvenile idiopathic arthritis is its childhood-onset counterpart. The two are increasingly regarded as the same disease beginning at different ages, although paediatric and adult treatment pathways may differ.
The diagnosis can be difficult because there is no single confirmatory test and because infection, malignancy and other inflammatory diseases can produce a similar picture. Ferritin is an important clue, but it must be interpreted in context.
Treatment has moved beyond prolonged reliance on corticosteroids. IL-1 and IL-6 inhibitors now have a central role, with the aim of controlling inflammation promptly and achieving remission without ongoing steroid treatment.
Above all, clinicians and patients need to remain alert to macrophage activation syndrome. Persistent fever, rapidly changing blood results and sudden clinical deterioration require urgent assessment.
Careful diagnosis, early control of inflammation and structured monitoring can substantially improve the outlook for people living with Still’s disease.
Please note, these posts are for general information only and do not constitute medical advice. Dr Singh would encourage you to speak to your healthcare professional to be assessed and managed for your specific symptoms.