🦵 OA vs RA Differential Diagnosis Simulator

Pain Character — Mechanical Wear vs Inflammatory Flare

OA pain worsens with use; RA pain flares with rest and inflammation.

• Mechanical: OA Pain Pattern (worse with activity)
• Inflammatory: RA Pain Pattern (worse after rest)
• >50: OA Typical Onset Age (gradual over years)
• 30–60: RA Typical Onset Age (weeks to months)

How OA pain behaves

Pain increases through the day, eases with rest.

How RA pain behaves

Pain and swelling dominate mornings and after inactivity.

Systemic clues

RA often brings fatigue, low fever, and malaise; OA rarely does.

Stiffness Duration — the Classic 30-Minute Cutoff

Stiffness under 30 minutes points to OA; over an hour points to RA.

• <30 min: OA Stiffness Duration (brief, localized)
• >60 min: RA Stiffness Duration (prolonged, diffuse)
• OA trait: Gel Phenomenon (brief stiffness after rest)
• High: ACR/EULAR Weight (stiffness in RA criteria)

Why RA stiffness lasts longer

Ongoing synovial inflammation keeps joints stiff for hours.

Why OA stiffness resolves fast

Cartilage wear causes brief gelling, not sustained inflammation.

Using the slider

Drag stiffness duration and watch RA likelihood climb past 60 minutes.

Symmetry Pattern — Which Joints, and How Many Sides

RA strikes symmetric small joints; OA favors asymmetric load-bearing ones.

• Bilateral: RA Symmetry (same joints, both sides)
• Asymmetric: OA Symmetry (load-dependent side)
• MCP, PIP, wrist: RA Hallmark Joints (spares DIP joints)
• Knee, hip, DIP: OA Hallmark Joints (spares MCP joints)

RA joint map

Small hand joints, wrists, and MCPs light up on both hands.

OA joint map

Knees, hips, and DIP joints bear the wear pattern.

Symmetry score logic

Score rises as marker and stiffness inputs shift toward RA.

Lab Panel — CRP, ESR, RF, and Anti-CCP

Elevated CRP/ESR and positive RF or anti-CCP favor RA over OA.

• Elevated: CRP in RA (active synovitis)
• Normal: CRP in OA (non-inflammatory)
• ~95%: Anti-CCP Specificity (for RA diagnosis)
• ~70%: RF Sensitivity (positive in RA)

Reading the marker slider

Higher marker level simulates rising CRP, ESR, RF, and anti-CCP.

Why OA labs stay quiet

OA is degenerative, not autoimmune, so inflammatory labs stay normal.

Why RA labs spike

Autoantibodies and cytokines drive measurable systemic inflammation.

Final Call — Weighing the Combined Evidence

Stiffness, symmetry, and markers combine into one confidence score.

• 4: Inputs Combined (stiffness, symmetry, markers, joints)
• OA % vs RA %: Output (relative likelihood)
• Weighted sum: Confidence Basis (slider-driven)
• Screening aid: Clinical Use (not a replacement for exam)

How the verdict is computed

Stiffness and marker sliders drive a weighted RA-vs-OA score.

Reading the confidence bar

A wider red bar means stronger evidence for RA.

Next steps in real care

Imaging and rheumatology referral confirm what labs suggest.