Tetanus — DTM&H MCQ

Correct answer: A — Tetanus

Tetanus (A) is correct because the vignette describes trismus, painful muscle spasms and autonomic instability arising 9 days after a contaminated wound in a patient with uncertain vaccination status, matching the classic incubation and clinical pattern of Clostridium tetani neurotoxin (tetanospasmin) causing disinhibition of inhibitory spinal interneurones. UKHSA guidance notes an incubation period of 4 to 21 days, most commonly around 10 days, with generalised rigidity, spasms and autonomic disturbance being the hallmark presentation, exactly as described here. The contaminated soil-associated wound in a farmer and unclear immunisation history further raise pre-test probability, since spores are ubiquitous in soil and manure and non-immunised or partially immunised individuals are at highest risk. Why the other options are wrong: E. Rabies: causes hydrophobia, hypersalivation and encephalitic or paralytic features after an animal bite, typically with a much longer and more variable incubation (weeks to months), and trismus is not a defining feature. C. Bacterial meningitis: presents acutely with fever, neck stiffness, headache and photophobia, not trismus or painful generalised spasms, and progresses over hours to days rather than appearing 9 days after a limb wound. B. Strychnine poisoning: produces similar spasms and trismus but is due to acute toxin ingestion, has a rapid onset within minutes to hours, and lacks the wound and incubation history given. D. Hypocalcaemia: causes tetany and carpopedal spasm but not trismus, autonomic instability, or a temporal link to a contaminated wound. Key point: Trismus plus generalised spasms and autonomic instability roughly a week or more after a contaminated wound, especially with uncertain vaccination status, is classic for tetanus.

Reference: UKHSA Green Book, Chapter 30: Tetanus (2025), https://assets.publishing.service.gov.uk/media/683dceaa81deb72cce2680fc/Tetanus-green_book-chapter-30-02-06-25.pdf