DIP Episode 109 - USMLE Step 1 Rheumatology Review Part 2 (Final Part)

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 MC Ps and PI Ps, sparing the DI Ps; 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 DMAR Ds and second-line agents like TNF inhibitors.

Board exam buzzwords

Rapid review table

Board-speak -> diagnosis

Differential diagnosis / distinguishing features

Inflammatory Myopathies (PMR vs DM vs Fibromyalgia)

Connective Tissue Diseases (MCTD vs Scleroderma)

Neuromuscular Weakness (MG vs LEMS)

Management pearls

• RA Joint Care: Before any surgery involving neck manipulation, rule out atlantoaxial instability in patients with RA due to the risk of spinal cord compression or vertebral artery entrapment.
• Methotrexate Toxicity: If a patient requires long-term methotrexate therapy and develops myelosuppression/GI issues, rescue the bone marrow by administering leucovorin (folinic acid).
• TNF Inhibitor Use: Always screen for latent Tuberculosis (TB) via Tuberculin Skin Test or Quantiferon test before initiating TNF inhibitor therapy (e.g., Adalimumab, Infliximab).
• Sarcoidosis Hypercalcemia Management: Monitor calcium levels and consider Vitamin D analogues if hypercalcemia is severe; the underlying cause is granuloma activity on 1-\alpha-hydroxylase.

Don't miss

Integration & clinical reasoning

• Rheumatology & Neurology: RA can cause carpal tunnel syndrome (CTS) due to synovitis, and systemic autoimmune diseases like SLE or MCTD are associated with vasculitis and neuropathy.
• Endocrinology & Rheumatology: Sarcoidosis presents a unique overlap by causing hypercalcemia via Vitamin D metabolism dysregulation in the granulomas, linking endocrine and rheumatologic systems.
• Neurosurgery & Rheumatology: The risk of atlantoaxial instability in RA necessitates careful pre-operative imaging (lateral neck X-ray) to prevent spinal cord or vertebral artery injury during manipulation.

OMM / COMLEX integration

• Acute/Unstable Management Priority: In any acute presentation of severe weakness (e.g., suspected MG crisis), standard emergency management (IV therapy, respiratory support) takes absolute priority over OMT.
• Myasthenia Gravis Crisis: If the patient is experiencing a myasthenic crisis requiring mechanical ventilation, treatment with acetylcholinesterase inhibitors must be managed carefully in conjunction with neuromuscular blockade agents used for intubation/ventilation.

Concept connections / cross-references

• For detailed information on vasculitis associated with systemic autoimmune diseases, review [Episode 102].
• Understanding the pathophysiology of inflammatory myopathies and muscle enzyme elevation is related to general neuromuscular principles covered in [Episode 95].

High-yield association table

Key terms glossary

Study optimization

Question pattern recognition

• The "Best Answer" Trap: Questions often present a constellation of symptoms that mimic several diseases (e.g., polyarthralgia could be RA, PMR, or PsA). The key is identifying the single most specific diagnostic marker (antibody, enzyme level, physical finding) to narrow the differential.
• The "Exclusion" Pattern: Recognizing what a disease does not cause (e.g., MCTD sparing the kidneys; PMR having normal CK) is often more important than recognizing its primary features.

Test yourself

Common mistakes to avoid

Common traps