Stills Disease

Educational clinical summary of Stills Disease for doctors and students: definition, workup, management, and key caveats. Not a substitute for guidelines.

Maintained by Dr. Vivek Karn Review process: editorial policy

Disclaimer: This document provides comprehensive, evidence-based medical information for educational purposes and as a clinical reference. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical decisions must always be based on the individual patient's condition, available evidence, and the clinician's judgment. Always consult with a qualified healthcare professional for any health concerns or before making any decisions related to patient care.

Overview

Stills Disease, often referred to as Adult-Onset Still's Disease (AOSD) in adults and Systemic Juvenile Idiopathic Arthritis (sJIA) in children, is a rare, severe, systemic inflammatory disorder characterized by a classic triad of high spiking fevers, evanescent salmon-pink rash, and arthralgia/arthritis. It is a diagnosis of exclusion, requiring the elimination of infectious, neoplastic, and other rheumatic diseases.

Definition: A rare, multi-systemic inflammatory disorder characterized by unremitting daily fever spikes, evanescent rash, and arthralgia/arthritis, along with other systemic manifestations such as lymphadenopathy, hepatosplenomegaly, serositis, and leukocytosis. It is considered an autoinflammatory disease due to dysregulation of the innate immune system.
Epidemiology:
- Incidence: Estimated incidence of AOSD ranges from 0.16 to 0.4 per 100,000 population per year.
- Prevalence: Estimated prevalence around 1.5 per 100,000.
- Age: Typically affects young adults, with two peaks: 15-25 years and 35-45 years. sJIA affects children under 16 years.
- Sex: No significant sex predilection in AOSD, though some studies suggest a slight female predominance. sJIA affects males and females equally.
- Geographic/Ethnic: Occurs worldwide, no specific ethnic predominance identified.
Classification:
- Adult-Onset Still's Disease (AOSD): The focus of this document.
- Systemic Juvenile Idiopathic Arthritis (sJIA): The pediatric counterpart, sharing many clinical and pathophysiological features but with specific diagnostic criteria and age-related considerations.
- Clinical Course Subtypes (AOSD):
  - Monocyclic Systemic Course: Single episode, resolves within weeks to months without recurrence. Best prognosis.
  - Polycyclic Systemic Course: Recurrent episodes of systemic symptoms, with periods of remission between flares.
  - Chronic Articular Course: Persistent, destructive arthritis, often affecting large joints, with less prominent systemic features over time. Poorer prognosis due to joint damage.

Pathophysiology

AOSD is considered an autoinflammatory disorder, primarily driven by dysregulation of the innate immune system, leading to a "cytokine storm" characterized by overexpression of pro-inflammatory cytokines.

Mechanism:
- Cytokine Dysregulation: Central to AOSD pathogenesis. Key cytokines involved include:
  - Interleukin-1 beta (IL-1β): Plays a critical role in mediating systemic inflammation, fever, and acute phase reactants. Blockade of IL-1 is highly effective in many patients.
  - Interleukin-6 (IL-6): Contributes to fever, acute phase reactant production (e.g., CRP, ferritin), and B-cell activation. High levels correlate with disease activity.
  - Interleukin-18 (IL-18): Significantly elevated in AOSD, correlating with disease activity and potentially triggering macrophage activation syndrome (MAS). It promotes IFN-γ production.
  - Tumor Necrosis Factor-alpha (TNF-α): Also elevated, but less consistently effective as a therapeutic target compared to IL-1 and IL-6.
- Macrophage Activation: The hyperinflammatory state can trigger excessive activation and proliferation of macrophages and histiocytes, leading to hemophagocytosis, particularly within the bone marrow, lymph nodes, and liver. This can culminate in Macrophage Activation Syndrome (MAS), a life-threatening complication.
- Genetic Predisposition: No single gene identified, but associations with certain HLA alleles (e.g., HLA-DRB1, HLA-B17, HLA-B35) and polymorphisms in genes related to cytokine pathways (e.g., IL-1 gene cluster) have been reported, suggesting a polygenic susceptibility.
- Environmental Triggers: A preceding infection (viral or bacterial) is often reported anecdotally, suggesting environmental triggers may initiate the inflammatory cascade in genetically predisposed individuals.
Risk Factors:
- Genetic Susceptibility: As mentioned above, certain HLA types and cytokine gene polymorphisms.
- Infection: Possible role of viral (e.g., Epstein-Barr virus, cytomegalovirus, parvovirus B19) or bacterial infections as triggers, though not definitively proven.
- Demographics: Young adults (15-25, 35-45 years).
Protective Factors: None definitively identified.

Clinical Presentation

AOSD is characterized by a constellation of systemic and articular symptoms. The severity and prominence of features can vary.

Signs and Symptoms

Cardinal Features:
- Fever: Daily spiking fever (≥39°C or 102.2°F), usually occurring once or twice a day (often in the late afternoon or evening), returning to normal or subnormal between spikes. This quotidian or double-quotidian pattern is highly characteristic.
- Rash: Evanescent, salmon-pink, macular or maculopapular rash, typically appearing with fever spikes and often pruritic. Most commonly on the trunk, proximal extremities, face, and palms/soles. Koebner phenomenon (rash appearing at sites of trauma) can occur.
- Arthralgia/Arthritis: Joint pain is almost universal, preceding or occurring concurrently with systemic symptoms. Arthritis (objective synovitis) occurs in most patients, typically polyarticular and symmetrical, affecting knees, wrists, ankles, shoulders, elbows, and sometimes small joints of hands/feet. Wrist and ankle involvement is highly characteristic.
- Sore Throat (Pharyngitis): Common initial symptom, often precedes fever and other systemic manifestations, and can be misdiagnosed as an infection.
Early Signs:
- Fever (often the first symptom)
- Sore throat
- Myalgia/arthralgia
- Evanescent rash
- Fatigue
Advanced Signs:
- Persistent arthritis, potentially leading to chronic destructive changes (especially wrist, cervical spine ankylosis).
- Chronic systemic inflammation leading to complications like amyloidosis.
- Organ involvement: Hepatomegaly, splenomegaly, lymphadenopathy, pericarditis, pleuritis, interstitial lung disease, diffuse alveolar hemorrhage.
- Macrophage Activation Syndrome (MAS): A severe and potentially fatal complication characterized by uncontrolled activation and proliferation of well-differentiated macrophages and cytotoxic T lymphocytes, leading to systemic inflammation and hemophagocytosis.
Atypical Presentations:
- Predominantly articular disease with minimal systemic symptoms.
- Recurrent fever without other prominent features.
- Presentation dominated by a specific organ involvement (e.g., severe serositis, interstitial lung disease).
- Aferrile AOSD (rare).

Physical Examination

Inspection:
- Rash: Evanescent, salmon-pink, non-pruritic (or mildly pruritic), macular or maculopapular, often observed during fever spikes. May be linear (Koebner phenomenon).
- Joints: Swelling, erythema, warmth, limited range of motion (due to synovitis, effusions). Often affects knees, wrists (especially carpals), ankles.
- Overall: Appears acutely ill, signs of fatigue, possibly jaundice in severe hepatic involvement.
Palpation:
- Joints: Tenderness, warmth, swelling consistent with synovitis. Wrist carpal fusion or ankylosis may be palpable in chronic disease.
- Lymph nodes: Generalized lymphadenopathy, especially cervical, axillary, inguinal (mobile, non-tender).
- Abdomen: Hepatomegaly (smooth, non-tender), splenomegaly.
Special Tests:
- Musculoskeletal Exam: Assess range of motion, tenderness, swelling of all joints. Evaluate for signs of chronic damage (e.g., reduced wrist mobility, ankylosis).
- Cardiac Auscultation: Listen for pericardial friction rub (pericarditis), murmurs (rarely myocarditis).
- Pulmonary Auscultation: Listen for pleural rub (pleuritis), crackles (interstitial lung disease).

Diagnostic Approach

AOSD is a diagnosis of exclusion. There is no single diagnostic test. Diagnosis relies on a combination of clinical features and laboratory abnormalities, after ruling out other conditions. Yamaguchi or Fautrel criteria are commonly used for classification.

History Taking

Key Questions:
- Fever pattern: Daily spiking, peak temperature, duration, timing (e.g., evening).
- Rash characteristics: Timing relative to fever, appearance (color, flat/raised), location, itching.
- Joint symptoms: Onset, pattern (oligo/polyarticular, symmetrical/asymmetrical), joints involved, morning stiffness, severity, functional impact.
- Other systemic symptoms: Sore throat, myalgia, fatigue, weight loss, night sweats, lymphadenopathy, abdominal pain, chest pain (pleuritic/pericardial).
- Recent infections: Any preceding viral or bacterial illness, travel history.
- Medications: Any new medications or drug allergies (to rule out drug reactions).
- Family history: Autoimmune diseases, cancer.
- Symptoms suggestive of MAS: Unexplained bleeding/bruising, neurological changes, severe fatigue, rapid deterioration.
Red Flags:
- Rapid clinical deterioration: Suggests complications like MAS.
- New neurological symptoms: Seizures, altered mental status.
- Significant hemorrhage: Due to coagulopathy in MAS.
- Sudden onset of severe abdominal pain: May indicate visceral organ involvement or other acute abdominal pathology.
- Persistent symptoms despite initial therapy: May indicate resistant disease or incorrect diagnosis.

Laboratory Tests

First-Line:
- Complete Blood Count (CBC) with differential:
  - Leukocytosis: Typically >10,000/µL (often 15,000-30,000/µL) with neutrophilia (>80%).
  - Anemia: Normocytic, normochromic anemia of chronic disease.
  - Thrombocytosis: Common during active disease.
- Inflammatory markers:
  - Erythrocyte Sedimentation Rate (ESR): Markedly elevated (>50 mm/hr, often >100 mm/hr).
  - C-Reactive Protein (CRP): Markedly elevated.
- Ferritin:
  - Serum Ferritin: Markedly elevated, often >1000 ng/mL, and can be extremely high (>5000 ng/mL or even >10,000 ng/mL). Highly characteristic.
  - Glycosylated Ferritin: Low percentage (<20%) is highly specific for AOSD (and MAS), though not universally available.
- Liver Function Tests (LFTs): Elevated AST, ALT, LDH (often disproportionately elevated LDH), and sometimes bilirubin.
- Renal Function Tests: BUN, Creatinine (usually normal, but monitor in severe cases or MAS).
- Coagulation Profile: PT, aPTT, Fibrinogen (for MAS screening, can be abnormal).
- Exclusion of Infections: Blood cultures, urine cultures, viral serologies (e.g., EBV, CMV, HIV, hepatitis panel), tuberculin skin test (PPD) or interferon-gamma release assay (IGRA).
- Exclusion of Malignancy: Age-appropriate cancer screening, protein electrophoresis (to rule out lymphoma/leukemia).
- Autoimmune serology:
  - Rheumatoid Factor (RF): Negative (<1:40) in >95% of cases.
  - Antinuclear Antibody (ANA): Negative (<1:80) in >95% of cases.
  - Anti-CCP: Negative.
Confirmatory (Diagnostic Criteria - Diagnosis of Exclusion):
- Yamaguchi Criteria (1992): Requires ≥5 criteria, including ≥2 major criteria.
  - Major Criteria:
    1. Fever ≥39°C lasting ≥1 week
    2. Arthralgia/arthritis lasting ≥2 weeks
    3. Characteristic salmon-pink rash
    4. Leukocytosis (≥10,000/µL) with ≥80% neutrophils
  - Minor Criteria:
    1. Sore throat
    2. Lymphadenopathy
    3. Hepatomegaly or splenomegaly
    4. Abnormal LFTs
    5. Negative RF and ANA
- Fautrel Criteria (2002): Requires ≥4 major and ≥1 minor, or ≥5 major criteria.
  - Major Criteria:
    1. Fever ≥39°C
    2. Typical rash
    3. Arthralgia
    4. Sore throat
    5. Neutrophilic leukocytosis (>10,000/µL)
  - Minor Criteria:
    1. Myalgia
    2. Lymphadenopathy
    3. Hepatomegaly or splenomegaly
    4. Pericarditis or pleuritis
  - Note: Negative RF and ANA are not criteria but are exclusionary.
- Bone Marrow Biopsy: May show hemophagocytosis in MAS, but not routine for AOSD diagnosis.
Monitoring:
- CBC with differential: Monitor for cytopenias (especially in MAS), leukocytosis.
- ESR, CRP, Ferritin: Track disease activity and response to treatment. Ferritin is particularly sensitive.
- LFTs: Monitor for hepatic involvement or drug toxicity.
- Coagulation Profile, D-dimer, Fibrinogen, Triglycerides: Essential for monitoring for MAS development or progression.
- Echocardiogram: Periodically if cardiac involvement (pericarditis, myocarditis) is suspected or for long-term follow-up.

Imaging

Recommended:
- Plain Radiographs (X-rays):
  - Joints: Initial X-rays of affected joints (e.g., wrists, knees) typically show soft tissue swelling and effusions in acute phase. In chronic disease, may show joint space narrowing, erosions, and characteristic carpal ankylosis (fusion of carpal bones) or cervical spine ankylosis (C2-C3, C3-C4).
- Chest X-ray: To evaluate for pleural effusions, pericardial effusions (enlarged cardiac silhouette), or interstitial lung disease.
- Echocardiogram: To assess for pericardial effusion, pericarditis, myocarditis, or pulmonary hypertension.
Advanced:
- Magnetic Resonance Imaging (MRI):
  - Joints: More sensitive than X-rays for detecting early synovitis, bone marrow edema, erosions, and cartilage abnormalities. Useful for evaluating subtle joint involvement or assessing extent of damage.
  - Abdomen: MRI of abdomen may be used to assess hepatosplenomegaly, lymphadenopathy, or rule out other abdominal pathology.
- Computed Tomography (CT) scan:
  - Chest/Abdomen/Pelvis: To assess for lymphadenopathy, hepatosplenomegaly, serositis, or to rule out lymphoma/other malignancies, especially when initial screening is equivocal. High-resolution CT (HRCT) of the chest for interstitial lung disease.
- Positron Emission Tomography (PET-CT): Can show diffuse metabolic activity in lymph nodes, spleen, bone marrow, and joints, reflecting systemic inflammation. Useful in distinguishing AOSD from occult malignancy or infection, but not routinely used for diagnosis.

Management

Management of AOSD is aimed at controlling systemic inflammation, preventing organ damage, and achieving remission. Treatment typically involves a stepwise approach, starting with corticosteroids and escalating to biologic agents if needed.

Acute Management

Immediate:
- Rule out life-threatening conditions: Sepsis, severe infection, malignancy, other rheumatological emergencies.
- High-dose NSAIDs: For mild symptoms and non-visceral involvement (e.g., ibuprofen 400-800 mg TID or naproxen 250-500 mg BID). Often insufficient for systemic symptoms.
- Systemic Glucocorticoids: The cornerstone of initial therapy for moderate to severe disease, especially with prominent systemic features or organ involvement.
  - Prednisone: Typically 0.5-1 mg/kg/day orally (up to 60 mg/day for most adults).
  - Methylprednisolone (IV): For severe cases or MAS (pulse therapy: 500-1000 mg IV daily for 3-5 days).
Stabilization:
- Monitor vital signs, inflammatory markers (ESR, CRP, ferritin), CBC, LFTs.
- Adjust glucocorticoid dose based on clinical response and laboratory parameters.
- If MAS is suspected, prompt initiation of specific MAS therapy (see Complications).
Emergency:
- Macrophage Activation Syndrome (MAS):
  - Methylprednisolone pulse therapy: 10-30 mg/kg/day (max 1000 mg) for 3-5 days, then taper.
  - Cyclosporine A (CsA): 2-5 mg/kg/day, often added if no rapid response to steroids or in severe cases.
  - Anakinra (IL-1 inhibitor): Highly effective in MAS, often used in conjunction with steroids. Dosing for MAS: 2-8 mg/kg/day (up to 100 mg/dose) subcutaneously or intravenously, sometimes higher doses.
  - IVIG: May be considered in refractory cases.
  - Etoposide: For life-threatening refractory MAS, typically in consultation with hematology/oncology.

Chronic Management

Pharmacological:
- Glucocorticoids: Tapered slowly once systemic symptoms are controlled. Many patients require a low maintenance dose for prolonged periods.
- Disease-Modifying Antirheumatic Drugs (DMARDs): Used as steroid-sparing agents and to control chronic disease.
  - Methotrexate (MTX): Oral or subcutaneous, 10-25 mg/week. Often the first conventional DMARD used.
  - Leflunomide, Azathioprine, Cyclophosphamide: Less commonly used, generally for refractory cases or specific organ involvement, or as alternatives to MTX.
- Biologic Agents: Highly effective, particularly targeting IL-1, IL-6, and IL-18 pathways.
  - IL-1 Inhibitors: First-line biologics, especially for systemic features.
    - Anakinra: 100 mg SC daily. Rapid onset of action, good for acute flares and MAS.
    - Canakinumab: 150 mg SC every 4 weeks. Long-acting, effective for sustained disease control.
  - IL-6 Inhibitors: Effective for both systemic and articular features.
    - Tocilizumab: 8 mg/kg IV every 4 weeks or 162 mg SC weekly.
  - IL-18 Inhibitors:
    - Tadekinig alfa: Investigational, targeting IL-18 binding protein. Not yet widely approved for AOSD.
  - TNF-α Inhibitors (e.g., Infliximab, Adalimumab, Etanercept): Generally less effective than IL-1 or IL-6 inhibitors in AOSD, especially for systemic symptoms. May be considered if articular disease predominates or other biologics fail.
Non-pharmacological:
- Physical and Occupational Therapy: Essential for maintaining joint function, range of motion, and preventing deformities, particularly in patients with chronic articular involvement.
- Pain Management: NSAIDs (if tolerated and not contraindicated), analgesics, topical agents.
- Nutritional Support: Address weight loss, ensure adequate intake, especially during periods of high inflammation.
- Patient Education: Disease understanding, medication adherence, recognition of flare symptoms and complications (especially MAS).
- Psychological Support: Chronic illness can impact mental health; consider counseling or support groups.
Monitoring:
- Regular clinical assessments (every 1-3 months during active disease, less frequently in remission).
- Monthly or bi-monthly laboratory monitoring of inflammatory markers (ESR, CRP, ferritin), CBC, LFTs, and renal function.
- Monitor for side effects of medications (e.g., infections with biologics, glucocorticoid side effects).
- Annual imaging (X-rays) of affected joints in chronic articular disease to assess for damage progression.

Treatment Algorithms

First-Line:
1. Systemic Glucocorticoids: Prednisone 0.5-1 mg/kg/day (up to 60 mg/day) or pulse methylprednisolone for severe cases.
2. For initial milder cases without severe systemic features, NSAIDs may be tried first, but typically glucocorticoids are needed.
Second-Line (Steroid-Sparing/Add-on for incomplete response or relapse):
1. If systemic symptoms persist or corticosteroids cannot be tapered: Add a biologic agent, preferably an IL-1 inhibitor (anakinra or canakinumab), or an IL-6 inhibitor (tocilizumab). IL-1 inhibitors are often preferred, especially if there are features suggestive of high IL-1 activity or MAS risk.
2. For predominantly articular disease or as an initial steroid-sparing agent in less severe cases: Methotrexate 10-25 mg/week.
3. If response to first biologic is inadequate, switch to another biologic from a different class (e.g., from IL-1 inhibitor to IL-6 inhibitor).
Refractory Cases (Failure of multiple biologics or severe complications):
1. Consider combination biologic therapy (not well-established, generally not recommended due to increased infection risk).
2. Consider other immunosuppressants like Cyclosporine A (especially if MAS is a concern), Cyclophosphamide, or Rituximab (off-label, limited evidence).
3. Hematopoietic Stem Cell Transplantation (HSCT): A last resort for severe, refractory, life-threatening AOSD, particularly with recurrent MAS, in highly specialized centers.

Complications

AOSD can lead to significant morbidity and mortality due to systemic inflammation and chronic disease.

Common:
- Chronic Arthropathy: Persistent, destructive arthritis, particularly affecting wrists (carpal ankylosis), leading to significant functional impairment. Also shoulders, knees, hips, and cervical spine.
- Anemia of Chronic Disease: Due to ongoing inflammation.
- Glucocorticoid-related side effects: Osteoporosis, weight gain, diabetes, hypertension, increased infection risk, cataracts, avascular necrosis.
Serious:
- Macrophage Activation Syndrome (MAS): A life-threatening hyperinflammatory syndrome characterized by excessive activation of macrophages and T lymphocytes, leading to multi-organ dysfunction, hemophagocytosis, coagulopathy, and cytopenias. Signs include sudden drop in ESR (due to fibrinogen consumption), rising ferritin, rising D-dimer, cytopenias, transaminitis, hypertriglyceridemia.
- Cardiac Involvement:
  - Pericarditis: Most common cardiac manifestation, usually responsive to treatment.
  - Myocarditis: Less common but serious, can lead to heart failure or arrhythmias.
  - Constrictive Pericarditis: Rare long-term complication of recurrent pericarditis.
- Pulmonary Involvement:
  - Pleuritis: Common.
  - Interstitial Lung Disease (ILD): Less common but can be progressive and severe.
  - Pulmonary Arterial Hypertension (PAH): Rare but severe.
  - Diffuse Alveolar Hemorrhage (DAH): Rare and life-threatening.
- Hepatic Dysfunction: Ranging from mild transaminitis to severe hepatitis or acute liver failure (rare). Can be due to disease activity, MAS, or drug toxicity.
- Amyloidosis (AA type): A rare but serious long-term complication of chronic inflammation, primarily affecting kidneys, liver, spleen, and gastrointestinal tract.
Long-term:
- Joint deformities and disability: From chronic destructive arthritis.
- Increased susceptibility to infections: Due to immunosuppressive therapy and underlying disease.
- Psychological impact: Chronic pain and illness can lead to depression and anxiety.

Prognosis

The prognosis of AOSD is highly variable and depends on the disease course and complications.

Factors:
- Clinical Course:
  - Monocyclic systemic course: Best prognosis, often leading to complete remission without recurrence or chronic joint disease.
  - Polycyclic systemic course: Variable, with recurrent flares requiring intermittent treatment.
  - Chronic articular course: Poorer prognosis due to high risk of irreversible joint damage and long-term functional impairment.
- Severity of Systemic Symptoms: More severe systemic involvement, especially with visceral organ damage, initially may indicate a more aggressive course.
- Response to Therapy: Early and adequate response to conventional and biologic therapies improves outcomes.
- Development of Complications: MAS and chronic destructive arthritis are major negative prognostic indicators.
- Specific Prognostic Markers (less validated): High levels of ferritin (especially glycosylated ferritin), persistent transaminitis, and thrombocytopenia might indicate a higher risk for MAS.
Survival:
- Mortality rate varies, generally reported as 5-10%, but potentially higher in older series prior to widespread biologic use.
- Causes of death include MAS, severe infections (often therapy-related), severe visceral involvement (e.g., liver failure, cardiac complications), and amyloidosis.
Quality of Life:
- Can be significantly impaired, especially in those with chronic articular disease or recurrent flares.
- Pain, fatigue, functional limitations, and medication side effects impact daily activities and mental well-being.

Prevention

Primary prevention of AOSD is not possible as the exact etiology and triggers are unknown. Strategies focus on secondary and tertiary prevention.

Primary: None known.
Secondary (Early detection and intervention):
- High index of suspicion: For patients presenting with classic triad of fever, rash, and arthralgia, especially after ruling out common infections and malignancies. Early diagnosis and aggressive treatment can prevent irreversible organ damage and chronic arthritis.
- Prompt referral to Rheumatology: For suspected cases to initiate appropriate diagnostic workup and therapy.
Tertiary (Preventing complications):
- Aggressive disease control: Timely and effective use of corticosteroids and biologics to suppress inflammation and prevent organ damage and chronic joint destruction.
- Prophylaxis against infection: Given immunosuppressive therapies (e.g., PJP prophylaxis with high-dose steroids, vaccinations as appropriate).
- Bone health: Calcium and vitamin D supplementation, and bisphosphonates if indicated, for patients on long-term glucocorticoids to prevent osteoporosis.
- Monitoring for MAS: Regular surveillance of ferritin, D-dimer, CBC, LFTs, and coagulation profile in patients with active disease, particularly during flares, to detect MAS early.
- Physical therapy: To maintain joint mobility and strength, minimizing long-term disability from chronic arthritis.

Special Populations

Pediatric (Systemic Juvenile Idiopathic Arthritis - sJIA)

Overlap: sJIA is the pediatric counterpart of AOSD, sharing almost identical clinical and laboratory features and a similar cytokine-driven pathophysiology (IL-1, IL-6, IL-18).
Diagnostic Criteria: ILAR (International League of Associations for Rheumatology) criteria for JIA, with specific criteria for the systemic category.
Clinical Features: Similar to AOSD, with prominent daily fevers, rash, and arthralgia/arthritis. Younger children may present more with systemic symptoms and less with overt arthritis.
Complications: MAS is a major and highly concerning complication in sJIA, with higher reported incidence than in AOSD. Growth retardation, osteoporosis, and amyloidosis are also concerns.
Management: Similar principles, with high-dose corticosteroids as initial therapy. Biologics targeting IL-1 (anakinra, canakinumab) and IL-6 (tocilizumab) are highly effective and are increasingly used early in the disease course to prevent chronic joint damage and MAS. Methotrexate is also used.

Geriatric

Rarity: AOSD is less common in older adults.
Atypical Presentation: May have a less classic presentation, sometimes mimicking polymyalgia rheumatica or vasculitis, which can delay diagnosis. Fever may be less prominent, or rash may be absent.
Comorbidities: Increased prevalence of comorbidities and polypharmacy, which can complicate diagnosis and management. Glucocorticoid side effects may be more pronounced.
Increased diagnostic challenge: Higher index of suspicion for other conditions (e.g., infections, malignancy, giant cell arteritis).

Pregnancy

Disease Activity: AOSD activity can fluctuate during pregnancy. Some women experience improvement, others flares.
Medication Safety:
- Glucocorticoids: Generally considered safe during pregnancy. Prednisone is preferred as it is largely inactivated by the placenta.
- NSAIDs: Avoid in the third trimester due to risk of premature ductal arteriosus closure.
- Methotrexate: Contraindicated in pregnancy due to teratogenicity. Must be stopped prior to conception.
- Biologics:
  - Anakinra: Limited data, but generally considered compatible with pregnancy (Category B).
  - Tocilizumab: Limited data, some concern for placental transfer in later pregnancy, but overall risk appears low (Category B).
  - Canakinumab: Limited data, generally not preferred unless necessary.
- Counseling: Pre-conception counseling is crucial to discuss disease control, medication adjustments, and potential risks. Close monitoring during pregnancy is essential.

Comorbidities

Cardiovascular Disease: Increased risk due to chronic inflammation and steroid use.
Infections: Increased risk due to immunosuppressive therapy. Prophylaxis and prompt treatment of infections are critical.
Metabolic Syndrome: Long-term glucocorticoid use can contribute to diabetes, dyslipidemia, and hypertension.
Renal Disease: Rarely a primary manifestation, but AA amyloidosis can cause renal impairment.
Psychiatric Comorbidities: Depression and anxiety are common due to chronic illness and pain.

Clinical Pearls

Diagnostic:
- Diagnosis of Exclusion: Always rule out infections (bacterial, viral, fungal), malignancies (especially lymphoma), and other autoimmune diseases before confirming AOSD.
- Classic Triad: High spiking fever (quotidian/double-quotidian), evanescent salmon-pink rash, and arthralgia/arthritis are highly suggestive.
- "Ferritin First": Markedly elevated serum ferritin (>1000 ng/mL, often >5000 ng/mL) with a low percentage of glycosylated ferritin (<20%) is a key diagnostic clue and a highly sensitive and specific marker.
- Negative ANA/RF: While not part of diagnostic criteria, a negative ANA and RF (in >95% of patients) helps distinguish AOSD from other systemic rheumatic diseases.
- Elevated LDH: Often disproportionately elevated compared to other liver enzymes.
Treatment:
- Steroids are the cornerstone: Initial control of systemic symptoms almost always requires systemic glucocorticoids.
- Biologics for Systemic Disease: IL-1 inhibitors (anakinra, canakinumab) and IL-6 inhibitors (tocilizumab) are highly effective for systemic symptoms and often lead to rapid improvement and allow steroid tapering.
- Methotrexate for Articular Disease: More beneficial for chronic arthritis components and as a steroid-sparing agent, but may be less effective for acute systemic flares.
Pitfalls:
- Misdiagnosis: Common pitfalls include misdiagnosing AOSD as sepsis, viral infection, lymphoma, or other autoimmune conditions.
- Delayed diagnosis: Can lead to increased morbidity, organ damage, and risk of MAS.
- Over-reliance on NSAIDs: NSAIDs are rarely sufficient for controlling systemic AOSD, and delay in starting corticosteroids can be detrimental.
- Missing MAS: MAS can rapidly progress and is life-threatening. A sudden clinical deterioration, unexplained cytopenias, drop in ESR (with rising CRP/ferritin), rising D-dimer, high triglycerides, and liver dysfunction should trigger immediate evaluation for MAS.

Recent Updates

Guidelines:
- ACR/EULAR recommendations: While not a dedicated guideline for AOSD, recommendations for sJIA (which shares significant overlap) highlight the early use of biologic DMARDs (particularly IL-1 and IL-6 inhibitors) in patients with high disease activity or MAS risk, to prevent steroid dependence and long-term damage. These principles are often extrapolated to AOSD.
Evidence:
- Increasing evidence supports the efficacy of IL-1 and IL-6 inhibitors as first-line biologic agents in AOSD, demonstrating superior efficacy and tolerability compared to TNF-α inhibitors.
- Focus on personalized medicine and identifying biomarkers for predicting treatment response and risk of MAS.
- Ongoing research into the role of IL-18 and its inhibition (e.g., tadekinig alfa) as a therapeutic target.
Controversies:
- Optimal timing and sequencing of biologics: While IL-1 and IL-6 inhibitors are preferred, specific algorithms for when to switch or combine remain areas of active research.
- Long-term safety of biologics: Ongoing surveillance for rare side effects, especially with prolonged use.
- Role of MAS prophylaxis: Whether certain high-risk patients should receive preemptive IL-1 blockade is debated.
- Defining remission and criteria for treatment withdrawal: Challenging given the polycyclic nature for many patients.

Key References

Guidelines:
- 2011 ACR Recommendations for the Treatment of Juvenile Idiopathic Arthritis: Systemic JIA. Arthritis & Rheumatism, 2011. (While for sJIA, relevant given the overlap).
- EULAR recommendations for the management of adult-onset Still's disease: 2022 update. Annals of the Rheumatic Diseases, 2022 (Expected release, check for most current version). Note: As of my last update, the 2016 EULAR recommendations were the most widely cited, but updates are common.
  - Previous EULAR Guidance: The 2016 EULAR/ACR recommendations for the management of adult-onset Still's disease. Annals of the Rheumatic Diseases, 2016.
Studies:
- Yamaguchi M, et al. Criteria for classification of adult Still's disease. Arthritis & Rheumatism, 1992. (Original diagnostic criteria).
- Fautrel B, et al. A new set of classification criteria for adult-onset Still's disease. Arthritis & Rheumatism, 2002. (Alternative classification criteria).
- FitzGerald AA, et al. Anakinra for the treatment of adult-onset Still's disease: a 3-year multicenter, open-label study. Arthritis & Rheumatism, 2015. (Key study on IL-1 blockade).
- Giacomelli R, et al. Tocilizumab in adult-onset Still's disease: an open-label, multicentre study. Annals of the Rheumatic Diseases, 2013. (Key study on IL-6 blockade).
- Canna SW, et al. The 2016 classification criteria for macrophage activation syndrome complicating systemic juvenile idiopathic arthritis: A European League Against Rheumatism/American College of Rheumatology/Paediatric Rheumatology International Trials Organisation Collaborative Initiative. Arthritis & Rheumatology, 2016. (Important for MAS diagnosis, applicable to AOSD).
Reviews:
- Jamilloux Y, et al. Adult-onset Still's disease: from pathogenesis to treatment. Joint Bone Spine, 2020.
- Gerfaud-Valentin M, et al. Adult-onset Still's disease. Autoimmunity Reviews, 2014.
- Gabay C, et al. Adult-onset Still's disease: a review of the disease course and treatment options. Rheumatology (Oxford), 2010.