🤲 Symmetrical MCP + PIP + morning stiffness >60 mins → Rheumatoid Arthritis
🧩 DIP involvement + psoriasis + nail pitting → Psoriatic Arthritis
🚨 Single hot swollen joint → Aspirate first, diagnose later (septic until proven otherwise)
👣 Sudden red 1st MTP overnight + alcohol/seafood trigger → Gout
🦴 Mechanical pain worse with use + hard bony enlargement (DIP) → Osteoarthritis
🧔 Young male + inflammatory back pain + improves with exercise + HLA-B27 → Ankylosing Spondylitis
🌭 Sausage digit (whole finger/toe swollen) → Psoriatic Arthritis
🦠 Recent diarrhoea or urethritis + asymmetric lower limb arthritis → Reactive Arthritis
👁️ Uveitis + back pain → Think seronegative spondyloarthropathy
🫁 RA + breathlessness → Consider rheumatoid ILD
🩸 Recurrent joint bleeding in young male → Haemophilia (haemarthrosis)
🔥 Acute flare after diuretic use → Gout
🌙 Nocturnal back pain + alternating buttock pain → Inflammatory sacroiliitis
📉 High RF + anti-CCP + early erosions → Poor RA prognosis
🦶 Heel pain (Achilles insertion) → Enthesitis (PsA / AS)
📊 Normal CRP + chronic knee pain + crepitus → OA more likely
💊 RA patient with sudden monoarthritis → Exclude septic joint (immunosuppressed risk)
🧓 Elderly + acute swollen wrist/knee + chondrocalcinosis → Pseudogout (CPPD)
🧠 Neck pain in RA + neurological signs → Atlantoaxial subluxation
⚖️ Obese patient + knee pain + varus deformity → OA
🦵 Inflammatory back pain starting <40 years, insidious, >3 months → Axial spondyloarthritis
🔴 Very high CRP + toxic appearance + unable to weight bear → Septic arthritis
🟡 Joint pain + psoriasis but no obvious plaques → Check scalp, umbilicus, natal cleft

🧪 Blood Test Pattern Recognition Grid – Arthritis

Blood Pattern	Most Likely Diagnosis	Why It Fits
↑ ESR/CRP + RF+ + Anti-CCP+	🔥 Rheumatoid Arthritis	Autoimmune inflammatory synovitis; Anti-CCP highly specific
↑ ESR/CRP + RF negative + psoriasis history	🧩 Psoriatic Arthritis	Seronegative inflammatory arthritis
Very high CRP (>100) + ↑ WCC	🦠 Septic Arthritis	Acute bacterial infection
↑ Serum urate (may be normal in flare)	💎 Gout	Hyperuricaemia predisposes to crystal deposition
Normal inflammatory markers	🦴 Osteoarthritis	Non-inflammatory degenerative process
ANA+ + dsDNA+ + low complement	🦋 SLE with arthritis	Immune complex disease
HLA-B27+	🦴 Ankylosing Spondylitis / Axial SpA	Genetic association with seronegative spondyloarthropathies
Neutropenia + splenomegaly + RA	⚠️ Felty’s Syndrome	Complication of longstanding RA
Microcytic anaemia + chronic inflammation	🔥 RA (Anaemia of chronic disease)	Chronic inflammatory cytokine effect
Very high ferritin + fever + arthritis	🔥 Adult Still’s Disease	Inflammatory cytokine storm picture
Raised CK + muscle weakness	💪 Myositis (not primary arthritis)	Inflammatory myopathy rather than joint pathology
Raised ALP + bone pain + deformity	🦴 Paget’s (bone disease, not inflammatory arthritis)	Bone turnover disorder
Low vitamin D + bone pain	🌤️ Osteomalacia (mimic)	Metabolic bone disease
High platelets + inflammatory markers	🔥 Active inflammatory arthritis	Reactive thrombocytosis from inflammation

🦴 Common Causes of Arthritis – Clinical Comparison

Feature	🦴 Osteoarthritis (OA)	🔥 Rheumatoid Arthritis (RA)	🧩 Psoriatic Arthritis (PsA)	💎 Gout	🦠 Septic Arthritis
Pathology	Cartilage degeneration + osteophytes	Autoimmune synovitis → pannus → erosions	Seronegative inflammatory arthritis (enthesitis driven)	Monosodium urate crystal deposition	Bacterial infection within joint space
Onset	Slow, mechanical (years)	Subacute (weeks–months)	Variable, may be intermittent	Sudden (hours, often overnight)	Acute (hours–days)
Joint pattern	Often asymmetrical	Symmetrical small joints	Asymmetrical, oligoarticular common	Usually monoarticular initially	Usually monoarticular
Common joints	DIP, PIP, knees, hips, spine	MCP, PIP, wrists	DIP, MCP, spine, SI joints	1st MTP (podagra 👣)	Knee most common
Morning stiffness ⏰	< 30 mins	> 60 mins	> 30–60 mins	Severe during attack	Movement extremely painful
Pain pattern	Worse with use 🏃	Improves with movement	Improves with activity (axial disease)	Exquisite tenderness 🔥	Severe constant pain 🚨
Systemic features	None	Fatigue, weight loss, low-grade fever	Psoriasis plaques, nail pitting, dactylitis (“sausage digit” 🌭)	Fever possible	Fever, rigors, septic symptoms ⚠️
Extra-articular	None	Nodules, ILD, vasculitis, pericarditis	Enthesitis (Achilles), uveitis 👁️	Tophi (chronic)	Risk of bacteraemia/sepsis
Blood tests 🧪	Normal inflammatory markers	↑ ESR/CRP, RF+, Anti-CCP+	RF negative, ↑ CRP	↑ Serum urate (may be normal in flare)	↑ CRP, ↑ WCC
Joint aspirate	Non-inflammatory	Inflammatory (neutrophils)	Inflammatory	Needle-shaped negatively birefringent crystals 💎	Purulent fluid, positive Gram stain/culture 🦠
X-ray findings 🖼️	Osteophytes, sclerosis, joint-space narrowing	Marginal erosions, peri-articular osteopenia	“Pencil-in-cup” deformity ✏️	Overhanging erosions	Rapid joint destruction (late)
Key management 💊	Analgesia, physio, weight loss	Early DMARDs (methotrexate)	DMARDs/biologics (anti-TNF, IL-17)	NSAIDs/colchicine → urate-lowering therapy	URGENT IV antibiotics + joint washout 🚨
Exam tip 🎓	Hard, bony enlargement	Boggy, warm synovitis	DIP involvement + psoriasis	Red, hot, exquisitely tender 1st MTP	Single hot joint = septic until proven otherwise

🚨 Acute Monoarthritis – Do Not Miss Causes

Feature	🦠 Septic Arthritis	💎 Gout	🩸 Haemarthrosis
Onset	Acute (hours–days)	Sudden (often overnight)	Sudden (trauma or spontaneous)
Pain	Severe, constant 🚨	Exquisite tenderness 🔥	Pressure-type pain
Systemic features	Fever, rigors ⚠️	May have low-grade fever	Usually none
Joint appearance	Red, hot, very swollen	Red, shiny, swollen	Tense, swollen
Common joint	Knee	1st MTP (podagra 👣)	Knee (commonest)
Aspirate 🧪	Purulent, ↑ WCC, positive Gram stain	Needle-shaped negatively birefringent crystals 💎	Frank blood
Management	URGENT IV antibiotics + washout 🚨	NSAIDs/colchicine → urate-lowering therapy	Rest, aspiration, treat cause
Key exam rule	Any hot swollen single joint = septic arthritis until proven otherwise.

🧠 Seronegative Spondyloarthropathies

Feature	🧩 Psoriatic Arthritis	🦴 Ankylosing Spondylitis	🦠 Reactive Arthritis	🌿 IBD-Associated
HLA-B27	Sometimes +	Often + (>80%)	Often +	Sometimes +
Axial involvement	Possible	Primary feature	May occur	Can occur
Peripheral arthritis	Asymmetrical	Less common	Asymmetrical, lower limb	Often flares with bowel disease
Extra features	Psoriasis, nail pitting 🌿	Uveitis 👁️	Conjunctivitis + urethritis	IBD (Crohn’s/UC)
Classic clue 🎓	Dactylitis (“sausage digit” 🌭)	Young male + inflammatory back pain	Recent GI/GU infection	Joint pain parallels bowel flare
Imaging	Pencil-in-cup deformity ✏️	Bamboo spine 🎋	Enthesitis	Similar to other SpA
Management	DMARDs/biologics	NSAIDs → biologics (anti-TNF/IL-17)	NSAIDs, treat trigger	Treat IBD + biologics

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Arthritis Diagnosis Compared

🔥 Rapid Pattern Recognition Grid – Arthritis (Finals Shortcut)

🧪 Blood Test Pattern Recognition Grid – Arthritis

🦴 Common Causes of Arthritis – Clinical Comparison

🚨 Acute Monoarthritis – Do Not Miss Causes

🧠 Seronegative Spondyloarthropathies

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