Musculoskeletal and Skin: Osteoporosis, Psoriasis · USMLE Step 1

A patient with psoriasis experiences worsening symptoms after streptococcal pharyngitis. Which type of hypersensitivity is implicated?

  1. Type I hypersensitivity
  2. Type II hypersensitivity
  3. Type III hypersensitivity
  4. Type IV hypersensitivity
Show answer and explanation

Correct answer: Type IV hypersensitivity

Psoriasis is a Type IV (T-cell–mediated) hypersensitivity reaction, with T cells driving keratinocyte proliferation. Infections such as streptococcal pharyngitis can trigger or exacerbate disease activity.

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