Methotrexate Ulceration FBC — ORE Part 1 MCQ

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ModerateHuman Disease & Dental ManagementMethotrexate Ulceration FBCORE Part 1

A patient on long-term methotrexate and folic acid supplementation for rheumatoid arthritis presents with oral ulceration. Which investigation would best help differentiate between methotrexate-induced ulceration and recurrent aphthous ulceration?

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Correct answer: D — Full blood count

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

Answer: A – Full blood count. Methotrexate toxicity commonly causes bone marrow suppression presenting as pancytopenia, which will be evident on FBC (reduced RBC, WBC, platelets). Recurrent aphthous stomatitis has no haematological manifestation and FBC will be normal. This is the key differentiating feature. NHS guidance emphasises frequent FBC monitoring to detect myelosuppression in methotrexate-treated patients, specifically citing mouth ulcers as a warning sign requiring investigation. Distractors: LFTs (B) may be checked but are not discriminating; electrolytes/urea (C) are non-specific; CXR (D) is irrelevant; B12/folate (E) would be maintained by folic acid supplementation and do not differentiate the conditions.

Reference: NHS Specialist Pharmacy Service (2026). Managing interactions with methotrexate. https://sps.nhs.uk/articles/managing-interactions-with-methotrexate/