Thread by @Rheumat_Aravind

🧵 Autoimmune vs Infection — How to Tell the Difference FAST

Fever, rash, cytopenia, organ dysfunction?
Is it a flare or an infection?
In autoimmune patients, this is life or death.
Here’s how to think clearly under pressure 👇
#Rheumatology #MedTwitter #CriticalCare @IhabFathiSulima @DrAkhilX @Medicalinfo111 @JasmineNephro @Janetbirdope

1/
⚠️ Steroids mask infection symptoms.
💊 If your patient is immunosuppressed, always suspect infection first.

🎯 Rule: Infection is 5x more common than a flare in rheum patients with fever.

2/
📈 Fever pattern matters
🌡️ Intermittent + high spikes → Still’s, TB, MAS
🌡️ Persistent low-grade → lupus flare
🌡️ New-onset fever on immunosuppression → infection until proven otherwise

3/
🩸 CBC clues
🎯 Flare: cytopenia + low retic + hemolysis
🎯 Infection: neutrophilic leukocytosis
🧠 Pancytopenia with high ferritin = consider MAS or HLH

4/
🧪 CRP vs ESR
📌 CRP rises sharply in infection
📌 ESR high in chronic inflammation
🎯 In SLE, CRP is often normal during flares
🧠 CRP↑ + ESR↑ → think infection
🧠 ESR↑ + CRP normal → think flare

5/
🧬 Procalcitonin (PCT)
🎯 Helpful to distinguish bacterial infection from flare
⬆️ High PCT → bacterial infection
↔️ Low/normal PCT → autoimmune flare likely
⚠️ Exceptions: MAS, HLH, macrophage activation can falsely raise PCT

6/
🧪 Ferritin = dual-edge sword
🎯 High ferritin in infection, MAS, Still’s

10,000 = think MAS, HLH
📌 Always look at context + other markers (TG, AST, LDH)

7/
🫁 Imaging helps
🎯 New infiltrates on HRCT? Infection or DAH?
📌 DAH = hemoptysis + fall in Hb + normal CRP
🧠 Use BAL, cultures, procalcitonin to guide

8/
🧠 Neuro symptoms
🎯 Seizure + fever → rule out CNS infection first
Do CSF + MRI
📌 If sterile + ANA+, think NPSLE
⚠️ Never treat suspected NPSLE without ruling out infection

9/
💉 Drug timing helps
📌 Recent biologic start → screen for TB, PCP
📌 Rituximab → late-onset neutropenia, hypogammaglobulinemia
🧠 TNF inhibitors → fungal, TB, Listeria

10/
🧠 Final Rule: Treat Infection First If in Doubt
🎯 If your patient is sick, febrile, and immunosuppressed—
📌 Broad-spectrum antibiotics first
📌 Immunosuppression only after excluding infection
🧠 You can taper steroids later. You can’t reverse sepsis.

💡 Infection vs Flare is the most dangerous diagnostic trap in rheumatology.

🏁 Rule of thumb:
Sick + Immunosuppressed + Fever = Infection until proven otherwise

🔁 Share this to spread knowledge.
#RheumTwitter #Autoimmune #ClinicalPearls #InternalMedicine