4.11 Antibody Review

Rheumatology review for the USMLE Step 1 Exam.

ANA Principles

• ANA (Anti-Nuclear Antibody):
  • Non-specific antibody.
  • Reacts against nuclear antigens, including proteins, DNA, RNA, and nucleic acid-protein complexes.
  • Includes a group of antibodies such as anti-dsDNA, anti-histone, SSA/Ro, SSB/La, Scl-70, anti-aminoacyl-tRNA synthetase (Jo-1).
  • Found in 20-30% of the general public without connective tissue disorder symptoms.
• ANA+ individuals may or may not have a rheumatologic disorder.
• Further workup is needed in ANA+ cases to determine the specific disorder.

Antibodies by Disease Process

• Systemic Lupus Erythematosus (SLE)

  • Anti-dsDNA antibody.
  • Anti-Smith antibody.

• Drug-Induced Lupus

  • Anti-histone antibody.

• Diffuse vs. Limited Scleroderma

  • Diffuse: Anti-Scl-70 (anti-topoisomerase I).
  • Limited: Anti-centromere (often called CREST syndrome, with CREST standing for centromere).

• Sjogren's Syndrome

  • Anti-SSA (Ro).
  • Anti-SSB (La), which usually occurs in the presence of SSA.
  • SSA is considered the Sjogren-specific antibody, leading to the presence of SSB.

• Rheumatoid Arthritis (RA)

  • Anti-CCP (Cyclic Citrullinated Peptide).
  • RF (Rheumatoid Factor) is non-specific.

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