Radiation Trismus — ORE Part 1 MCQ

Instant feedback + full explanation. One question, done properly.

ModerateOral MedicineRadiation TrismusORE Part 1

A 50-year-old patient received radiotherapy for head and neck cancer 2 years ago, with the masticatory muscles within the treatment field. They now have persistent restricted mouth opening of 18 mm, without acute pain, facial swelling or fever. What is the most likely underlying cause?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Fibrosis of the masticatory muscles

Explanation lettering: D = shown as A · A = shown as C · E = shown as D · C = shown as E

A is correct. Head and neck radiotherapy can produce late fibrosis and stiffness in directly irradiated masticatory muscles, resulting in persistent trismus. The previous radiotherapy field and marked, non-acute reduction in mouth opening are the discriminating features. Temporomandibular osteoarthritis may limit movement but would not be specifically explained by irradiation of the masticatory muscles. Myofascial pain dysfunction usually has pain-related muscle dysfunction rather than progressive structural post-radiotherapy stiffness. Coronoid hyperplasia causes mechanical restriction but is unrelated to the treatment history. Acute odontogenic infection can cause trismus, but would be expected to present with acute pain, swelling and/or systemic features rather than isolated longstanding restriction 2 years after radiotherapy.

Reference: Cambridge University Hospitals NHS Foundation Trust. Radiotherapy – head and neck cancer team radiotherapy for head and neck cancers (late effect: jaw muscle tightening/trismus). https://www.cuh.nhs.uk/patient-information/radiotherapy-head-and-neck-cancer-team-radiotherapy-for-head-and-neck-cancers/