Low-Grade Fever in Rheumatology: When It’s Not Just a Viral Illness”

Patient has fever for weeks. Cultures are negative. Antibiotics don’t help.
Could it be autoimmune?
Here’s your stepwise approach to low-grade fever in rheumatologic diseases.
👇 #Rheumatology #MedEd #Autoimmunity #PUO #MedTwitter @DrAkhilX @IhabFathiSulima

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🌡️ Low-grade fever = Temperature between 99°F and 101°F (37.2–38.3°C)
Common in autoimmune disease — often the first or only symptom.

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🧠 Autoimmune causes to consider:
•SLE (especially with serositis or nephritis)
•AOSD / sJIA
•ANCA vasculitis
•PMR / GCA
•RA (flare or extra-articular)
•Sarcoidosis
•MAS / HLH
•Overlap syndromes

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🔬 Mechanisms of fever in autoimmunity:
•Cytokine storm (IL-1, IL-6, TNF-α)
•Immune complex-mediated inflammation
•Subclinical serositis
•Triggered macrophage activation

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📌 Clinical flags suggesting autoimmune fever:
•Fever with rash
•Fever + arthritis or serositis
•Fever + cytopenia or proteinuria
•Fever unresponsive to antibiotics
•Fluctuating or “quotidian” pattern (esp. AOSD)

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🧾 Don’t miss these mimics:
•TB, endocarditis, occult abscess
•Drug fever (esp. allopurinol, sulfasalazine)
•Malignancy (esp. lymphoma, myeloma)
•Factitious fever

Always rule out infection first, especially in immunosuppressed patients.

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🧪 Workup checklist:
•CBC with differential
•ESR, CRP
•ANA, ENA, RF, anti-CCP
•dsDNA, complements
•ANCA
•Ferritin (esp. AOSD/MAS)
•CXR, urine, blood cultures
•TSH, HIV, Quantiferon-TB
•USG abdomen / HRCT if needed

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📈 Patterns matter:
•Daily spiking fevers: AOSD
•Evening rise: TB, autoimmune
•Fever + chills: Think infection
•No fever when on steroids: Masked disease activity

Chart the pattern over days — very helpful clue!

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💊 How to treat:
•Start low-dose steroids only after ruling out infection
•Treat underlying disease (SLE, RA, vasculitis)
•In AOSD or MAS: high-dose steroids ± IL-1/IL-6 blockers
•Avoid blind antibiotic courses — they delay diagnosis

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🧠 Pearls:
•Fever + thrombocytopenia + high ferritin? → MAS
•Fever + purpura or hematuria? → AAV
•Fever + cytopenias + ANA+? → SLE
•Fever + arthritis + rash + neutrophilia? → AOSD
•Steroid response ≠ confirmation — always monitor closely

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🔁 Retweet if you’ve seen “culture-negative fever” turn out to be lupus, Still’s, or vasculitis.
🩺 Follow @Rheumat_Aravind for more clinical pearls where rheum mimics infection.