MSK & Rheumatology confusion pairs
11 MSK & Rheumatology topics students commonly mix up on Step 2 CK, each with the fastest separator, a side-by-side comparison, and a free practice question.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
- Rheumatoid arthritis vs OsteoarthritisProlonged morning stiffness over 60 minutes with symmetric MCP or PIP synovitis favors rheumatoid arthritis.
- SLE vs Drug-induced lupusRenal or CNS involvement with low complement strongly favors SLE over drug-induced lupus.
- Polymyalgia rheumatica vs Giant cell arteritisJaw claudication in a patient older than 50 with inflammatory pain is the fastest clue for giant cell arteritis.
- Septic arthritis vs Gout flarePositive synovial Gram stain or culture is the decisive separator for septic arthritis.
- GPA vs MPADestructive ENT granulomatous disease is the quickest discriminator for GPA over MPA.
- PAN vs GPA (Wegener)Pulmonary parenchymal involvement is the fastest discriminator, because GPA commonly affects lungs while PAN classically spares them.
- Gout vs Pseudogout (CPPD)Crystal birefringence on polarized synovial fluid microscopy is the key discriminator.
- Reactive arthritis vs Septic arthritisPurulent synovial fluid with positive Gram stain or culture identifies septic arthritis.
- Fibromyalgia vs Polymyalgia rheumaticaElevated ESR or CRP in a patient older than 50 with proximal morning stiffness points to polymyalgia rheumatica.
- Ankylosing spondylitis vs Mechanical back painImprovement with exercise and worsening with rest separates inflammatory axial disease from mechanical pain.
- Osteomyelitis acute vs Osteomyelitis chronicDraining sinus tract or sequestrum identifies chronic osteomyelitis.