Source / episode info

• **Episode:**109
• **Title:**Divine Intervention Episode 109 – USMLE Step 1 Rheumatology Review Part 2 (Final Part)
• **Published:**2019-06-06
• Source:Episode page

One-liner

This episode reviews key rheumatologic conditions including RA (joint pattern, antibodies), MCTD (anti-U1 RNP), Sarcoidosis (hilar adenopathy, hypercalcemia), and neuromuscular disorders like Myasthenia Gravis and Lambert-Eaton Syndrome, emphasizing differential diagnosis based on clinical presentation and lab markers.

High-yield summary

• Rheumatoid Arthritis (RA): Characterized by symmetric polyarthritis affecting the MCPs and PIPs, sparing the DIPs; associated with anti-CCP antibodies (more specific) and potential Type III hypersensitivity reactions (RF/IgM against IgG).
• Inflammatory Myopathies: Differentiation is key: PMR has elevated ESR/CRP but normal CK; Dermatomyositis (DM) shows high ESR/CRP and elevated CK. Fibromyalgia presents with widespread pain, normal inflammatory markers, and normal muscle enzymes.
• Sarcoidosis: Classic findings include bilateral hilar lymphadenopathy ("1-2-3 sign"), restrictive lung disease (ILD), erythema nodosum, and hypercalcemia due to granuloma-mediated 1--hydroxylase activity on Vitamin D metabolism.
• Neuromuscular Junction Disorders: Myasthenia Gravis (MG) presents with fluctuating weakness and ocular symptoms (ptosis/diplopia); Lambert-Eaton Syndrome (LEMS) causes proximal weakness that improves with use (incremental response).
• MCTD vs Scleroderma: MCTD is defined by positive anti-U1 RNP antibodies, but critically, it typically spares the kidneys, unlike systemic sclerosis.

Learning objectives

• Differentiate the clinical presentation and lab findings among various inflammatory arthritides (RA, PsA, PMR).
• Recognize the classic signs and pathophysiology of sarcoidosis, including hypercalcemia mechanisms.
• Master the differential diagnosis between Myasthenia Gravis and Lambert-Eaton Syndrome based on muscle weakness patterns and diagnostic tests.
• Identify the key autoantibodies associated with systemic connective tissue diseases (e.g., anti-U1 RNP for MCTD).
• Understand the management principles of inflammatory myopathies, including DMARDs and second-line agents like TNF inhibitors.

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