Adult-onset Still's disease.
Adult-onset Still's disease (AOSD) is a rare autoinflammatory (not autoimmune) condition characterized by daily spiking fevers, a transient salmon-pink rash, arthritis, sore throat, and dramatically elevated ferritin (often 5–10 times the upper limit of normal). It is driven by IL-1, IL-6, and IL-18 — which is why IL-1 inhibitors (anakinra, canakinumab) and IL-6 blockers (tocilizumab) are highly effective. Glycosylated ferritin under 20% supports the diagnosis. AOSD is treatable, but recognition is the bottleneck.
The mechanism, the autoinflammatory disease that hides as fever of unknown origin.
AOSD is autoinflammatory rather than autoimmune — driven by innate immunity, not autoantibodies. Four mechanisms drive what patients experience:
IL-1 / IL-6 / IL-18 axis
AOSD is driven by innate immune cytokines — IL-1β, IL-6, and especially IL-18. This is fundamentally different from autoimmune diseases driven by T cells and autoantibodies, and it explains why IL-1 inhibitors are so effective.
Quotidian fever pattern
The classic fever pattern is 'quotidian' — daily spikes to 39°C or higher, typically in the evening or early morning, returning to normal between spikes. This pattern alone narrows the differential significantly.
Ferritin as a biomarker
Ferritin in AOSD is often 5–10 times the upper limit of normal — sometimes over 10,000 ng/mL. Glycosylated ferritin under 20% is highly suggestive of AOSD or macrophage activation syndrome (MAS), distinguishing it from other causes of hyperferritinemia.
Macrophage activation syndrome risk
AOSD can trigger MAS, a life-threatening hyperinflammatory complication characterized by very high ferritin, cytopenias, liver dysfunction, and hemophagocytosis. MAS is a medical emergency.
The 4-step plan, applied to AOSD.
Get the right diagnosis
Yamaguchi criteria are the standard. Exclude infection (blood cultures, serology), malignancy (especially lymphoma), and other autoinflammatory or vasculitic causes. Ferritin level and glycosylated ferritin percentage support the diagnosis. Imaging to evaluate for organomegaly and effusions.
Learn more about labs →Clean up your food
Anti-inflammatory Mediterranean pattern. Maintain hydration during fevers. Adequate protein supports recovery between flares.
AOSD & diet →Detox your daily life
Less established for AOSD specifically than for autoimmune diseases. General anti-inflammatory environmental approach applies. Manage stress, which can amplify symptom perception.
AOSD & environment →Build a stronger body
Gentle activity when symptoms are controlled. Resistance training preserves muscle during long steroid courses. Build conditioning between flares.
AOSD & exercise →
Go deeper.
Common misconceptions.
"Still's disease is just a kids' disease."
Systemic juvenile idiopathic arthritis (sJIA) is the pediatric form. Adult-onset Still's disease (AOSD) is the adult equivalent — same disease biology, same treatment options, just diagnosed after age 16. It's rare but real, and recognition matters.
"It's just fever of unknown origin — there's nothing to treat."
AOSD is highly treatable. Once recognized, IL-1 inhibitors (anakinra, canakinumab) and IL-6 inhibitors (tocilizumab) produce dramatic responses. Many patients achieve sustained remission. The 'untreatable' framing reflects pre-biologic-era thinking.
"Steroids alone will control it."
Steroids work in the short term but relapse rates are high and side effects accumulate over the years AOSD patients often need treatment. Steroid-sparing agents — typically IL-1 inhibitors as first line now — are essential for long-term control.
When to see a rheumatologist.
See a rheumatologist if you have:
- Daily spiking fevers above 39°C lasting more than 1 week
- Transient salmon-pink rash that appears with fever and fades when temperature normalizes
- Sore throat at the onset of illness
- Joint pain or arthritis plus fever
- Ferritin over 5,000 ng/mL on a routine lab
- Lymphadenopathy and hepatosplenomegaly plus fever
- Negative infection and malignancy workups despite persistent symptoms
AOSD is a diagnosis of exclusion — infection and malignancy must be ruled out first. But once that workup is negative and the pattern fits, do not delay treatment. MAS is a real risk.
- Yamaguchi M, et al. Preliminary criteria for classification of adult Still's disease. J Rheumatol, 1992. PubMed 1578458
- Mitrovic S, Fautrel B. Adult-onset Still's disease. Best Pract Res Clin Rheumatol.
- Nordström D, et al. Beneficial effect of anakinra in adult-onset Still's disease. J Rheumatol.
- Fautrel B, et al. Adult-onset Still disease: French AID Network expert recommendations. Joint Bone Spine.