Source / episode info

• **Episode:**108
• **Title:**Divine Intervention Episode 108 – ABIM/Medicine ITE/USMLE Step 3 Review Series 7 (Rheumatology 1)
• **Published:**2019-05-31
• Source:Episode page

One-liner

This episode provides a comprehensive comparison of Osteoarthritis and Rheumatoid Arthritis, detailing classic physical exam signs (e.g., RA's swan neck deformity vs. OA's Heberden's nodes), diagnostic criteria (joint fluid analysis, specific antibodies like anti-CCP), high-yield complications (Felty syndrome, vasculitis), and the complex pharmacology of DMARDs, including pregnancy safety and toxicity management.

High-yield summary

• OA vs RA Joint Pattern: OA is typically asymmetric, affects DIPs/first CMC joint primarily, and causes bony overgrowth (osteophytes). RA is symmetric, affects MCPs/wrists prominently, and spares the DIPs.
• Inflammatory Markers: Inflammatory arthritis shows elevated ESR/CRP, warm/red joints, prolonged morning stiffness (>1 hour), and highly inflammatory synovial fluid (WBC >2000, Neutrophil % >75%).
• RA Diagnostic Criteria: Key antibodies include Rheumatoid Factor (RF) (IgM anti-IgG) and the more specific Anti-CCP antibody. Imaging classically shows periarticular osteopenia and marginal erosions.
• DMARD Management Pearls: Methotrexate is a folate antagonist; its toxicity requires monitoring of LFTs, PFTs (reduced DLCO), and managing bone marrow suppression by administering Leucovorin (Folinic acid) rescue.
• Pregnancy Safety: The two DMARDs considered safe in pregnancy are Hydroxychloroquine and Sulfasalazine. Methotrexate and Leflunomide are teratogenic.
• RA Complications & Screening: High suspicion for Felty syndrome (RA + Neutropenia + Splenomegaly) is warranted, and all patients starting TNF inhibitors require screening for latent Tuberculosis (TB).

Learning objectives

• Differentiate the clinical presentation, joint distribution, and radiographic findings of Osteoarthritis versus Rheumatoid Arthritis.
• Identify key diagnostic markers for RA (RF, anti-CCP) and associated complications (Felty syndrome).
• Understand the mechanism of action and toxicity profile of Methotrexate and other DMARDs, including folate antagonism and rescue therapy.
• Apply knowledge of drug safety in pregnancy when selecting appropriate rheumatologic agents.
• Recognize high-risk patient populations for atlantoaxial instability due to chronic inflammatory arthritides.