A 47-year-old woman comes to the physician because of progressive pain and stiffness in her hands and wrists for the past several months. Her hands are stiff in the morning; the stiffness improves as she starts her chores. Physical examination shows bilateral swelling and tenderness of the wrists, metacarpophalangeal joints, and proximal interphalangeal joints. Her range of motion is limited by pain. Laboratory studies show an increased erythrocyte sedimentation rate. This patient's condition is most likely associated with which of the following findings?

IgM antibodies against the Fc region of IgG

HLA-B27 protein on white blood cells

HLA-A3 proteins on white blood cells

HLA-DQ2 proteins on white blood cells

IgG antibodies with a TNF-α binding domain on the Fc region

A 42-year-old woman presents complaining of pain in her hands. She reports that the pain is in both hands, and that it is usually worse in the morning. She reports that her hands are also stiff in the morning, but that this gradually improves throughout the morning. She notes, however, that her symptoms seem to be getting worse over the last three months. What is the most likely pathogenesis of her disease process?

Production of antibodies against antibodies

Production of antibodies against smooth muscle

Anti-neutrophil cytoplasmic antibody production

Type 1 hypersensitivity reaction

A 33-year-old woman presents to her primary care physician for gradually worsening pain in both wrists that began several months ago. The pain originally did not bother her, but it has recently begun to affect her daily functioning. She states that the early morning stiffness in her hands is severe and has made it difficult to tend to her rose garden. She occasionally takes ibuprofen for the pain, but she says this does not really help. Her medical history is significant for diabetes mellitus and major depressive disorder. She is currently taking insulin, sertraline, and a daily multivitamin. The vital signs include: blood pressure 126/84 mm Hg, heart rate 82/min, and temperature 37.0°C (98.6°F). On physical exam, her wrists and metacarpophalangeal joints are swollen, tender, erythematous, and warm to the touch. There are no nodules or vasculitic lesions. Which of the following antibodies would be most specific to this patient’s condition?

Anti-cyclic citrullinated peptide

A 27-year-old woman presents to her primary care physician with a chief complaint of pain in her hands, shoulders, and knees. She states that the pain has lasted for several months but seems to have worsened recently. Any activity such as opening jars, walking, or brushing her teeth is painful. The patient has a past medical history of a suicide attempt in college, constipation, anxiety, depression, and a sunburn associated with surfing which was treated with aloe vera gel. Her temperature is 99.5°F (37.5°C), blood pressure is 137/78 mmHg, pulse is 92/min, respirations are 14/min, and oxygen saturation is 98% on room air. Laboratory values are obtained and shown below. Hemoglobin: 9 g/dL Hematocrit: 33% Leukocyte count: 2,500/mm^3 with normal differential Platelet count: 107,000/mm^3 Serum: Na+: 139 mEq/L Cl-: 102 mEq/L K+: 4.4 mEq/L HCO3-: 24 mEq/L BUN: 21 mg/dL Glucose: 90 mg/dL Creatinine: 1.0 mg/dL Ca2+: 10.2 mg/dL AST: 12 U/L ALT: 10 U/L Which of the following is the most likely to be found in this patient?

Anti-cyclic citrullinated peptide antibodies

Degenerated cartilage in weight bearing joints

Systemic autoimmune diseases for USMLE Step 3: High-Yield Pathology Lessons

Autoimmune Principles - When Self Becomes Foe

Loss of Self-Tolerance: Breakdown of mechanisms that prevent immune responses against self-antigens.
- Central Tolerance: Failure to eliminate self-reactive T-cells (thymus) & B-cells (bone marrow).
- Peripheral Tolerance: Ineffective anergy or suppression by regulatory T-cells (Tregs) in circulation.

Mechanisms of Injury (Hypersensitivity):
- Type II: Antibodies target cell surfaces/extracellular matrix.
- Type III: Immune complex deposition.
- Type IV: T-cell mediated inflammation.

⭐ Many autoimmune diseases are strongly associated with specific HLA subtypes (e.g., HLA-B27 in ankylosing spondylitis).

Systemic Lupus Erythematosus - The Great Imitator

Diagnosis: Multisystem inflammation, often in young women. Use 📌 SOAP BRAIN MD mnemonic for criteria.
- Serositis, Oral ulcers, Arthritis, Photosensitivity
- Blood (cytopenias), Renal (nephritis), ANA, Immunologic, Neurologic
- Malar rash, Discoid rash
Autoantibodies:
- ANA: Best screening test (>95% sensitive).
- Anti-dsDNA: Specific, correlates with disease activity (especially nephritis).
- Anti-Sm: Most specific, but only in 20-30% of patients.
- Anti-histone: Associated with drug-induced lupus.
Pathology:
- Kidney: "Wire loop" lesions in diffuse proliferative glomerulonephritis.
- Heart: Libman-Sacks endocarditis (nonbacterial, verrucous).

Systemic Lupus Erythematosus (SLE) Symptoms

⭐ While ANA is the most sensitive antibody for screening, anti-dsDNA and anti-Sm are highly specific for diagnosis.

Sjögren's & Scleroderma - Dry and Hard Times

Feature	Sjögren's Syndrome	Scleroderma (Systemic Sclerosis)
Pathology	Lymphocytic infiltration of exocrine glands (salivary, lacrimal).	Widespread connective tissue fibrosis & vascular damage.
Hallmark	Sicca Syndrome: dry eyes (keratoconjunctivitis) & dry mouth (xerostomia).	Skin hardening (sclerodactyly) & Raynaud phenomenon.
Antibodies	Anti-Ro (SSA), Anti-La (SSB).	Anti-Scl-70 (diffuse), Anti-centromere (limited).

⭐ Patients with Sjögren's have a ~40x increased risk of developing B-cell lymphoma (e.g., MALT lymphoma).

Sjögren's vs. Scleroderma Histopathology

Inflammatory Myopathies - Muscle & Mixed Mayhem

Dermatomyositis (DM): Proximal muscle weakness plus skin findings.
- Rash: Heliotrope (eyelids), Gottron's papules (knuckles).
- Biopsy: Perimysial inflammation, perifascicular atrophy.
- Antibodies: Anti-Mi-2, anti-Jo-1.
Polymyositis (PM): Proximal muscle weakness, no skin findings.
- Biopsy: Endomysial inflammation (CD8+ T cells).
- Antibody: Anti-Jo-1.
Mixed Connective Tissue Disease (MCTD): Overlap features of SLE, systemic sclerosis, and polymyositis.
- Antibody: Anti-U1 RNP.

⭐ Dermatomyositis in adults is often a paraneoplastic syndrome (e.g., ovarian, lung, gastric cancer).

High‑Yield Points - ⚡ Biggest Takeaways

SLE: ANA (sensitive), anti-dsDNA/Sm (specific). Presents with malar rash, photosensitivity, and nephritis.

Sjögren Syndrome: Dry eyes and dry mouth (sicca). Associated with anti-Ro/SSA and anti-La/SSB antibodies.

Scleroderma: Widespread fibrosis. Limited/CREST type has anti-centromere Ab; Diffuse has anti-Scl-70 Ab.

Polymyositis/Dermatomyositis: Proximal muscle weakness, Gottron's papules, and anti-Jo-1 Ab.

Immune complex deposition (Type III HSR) is a key mechanism of tissue injury.

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