Polyarticular arthritis = involvement of >5 joints.
First step ➝ decide if inflammatory vs non-inflammatory.
Inflammatory = more pain, swelling, erythema, night pain 🌙, prolonged morning stiffness ⏰.
Non-inflammatory = mechanical pain, worse with activity, improves with rest.

👥 Age & Gender Related Differentials

Young adults
- Reactive arthritis (M > F)
- Systemic lupus erythematosus (F > M)
- Ankylosing spondylitis (M > F)
- Rheumatoid arthritis (F > M)
- Sjögren’s syndrome (F > M)
- Psoriatic arthritis
- Enteropathic arthritis (IBD-associated)
Middle age
- Gout (M > F)
- Osteoarthritis
- Rheumatoid arthritis (F > M)
Elderly
- Osteoarthritis
- Polymyalgia rheumatica
- Pseudogout (CPPD)

🚨 Joint sepsis is an emergency → requires urgent joint aspiration & antibiotics. Never miss it!

📝 Key Differentials (summary table)

Condition	Comments / Clues
🤲 Rheumatoid arthritis	Symmetrical small joints (MCP, PIP). Spares hips/DIPs. Morning stiffness >1 hr. Elevated CRP/ESR, +Anti-CCP, RF+. Joint aspiration if uncertain (exclude sepsis).
🔄 Reactive arthritis	Follows infection (GU/GI). Asymmetrical oligoarthritis. May have rash, urethritis, conjunctivitis. Consider viral or Lyme disease.
🦴 Osteoarthritis	DIP (Heberden’s), PIP (Bouchard’s), knees, hips, spine. Non-inflammatory. Bloods normal. Pain worse with use.
🧴 Psoriatic arthritis	Asymmetrical. PIP & DIP joints. Nail pitting, onycholysis, psoriatic rash. "Sausage digits".
🧍 Ankylosing spondylitis	Younger males. Axial back pain, sacroiliitis. Improves with activity. Large joints may be involved.
🦋 Systemic lupus erythematosus	Females. Symmetrical small joints. Synovitis but non-erosive. Butterfly rash, systemic features.

🩺 Clinical Exam

Inflammatory arthritis ➝ erythema, warmth 🔥, swelling, tenderness.
Non-inflammatory ➝ swelling & crepitus without warmth (e.g. OA).
Crepitus without erythema = degenerative change.

📌 General Guidance

Morning stiffness >1 hour, symmetric rest pain = inflammatory 🔥.
Pain worse with activity, better at rest = non-inflammatory ⚙️.
CRP/ESR → help distinguish inflammation (CRP better in acute setting).
Gout ➝ confirm by crystals (monosodium urate on polarised light). Serum uric acid alone is not diagnostic.
OA ➝ non-inflammatory, often pauci-articular, weight-bearing joints.
ANA sub-serologies ➝ only test if ANA positive + strong clinical suspicion.
Lyme ➝ test only if exposure risk + suggestive features.

📚 References

AAFP – Differential Diagnosis of Polyarticular Arthritis

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Polyarticular arthritis

📖 About

👥 Age & Gender Related Differentials

📝 Key Differentials (summary table)

🩺 Clinical Exam

📌 General Guidance

📚 References

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