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Azathioprine – Macrocytosis — SCE Neurology MCQ

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ModeratePeripheral Neuropathy & NeuromuscularAzathioprine – MacrocytosisSCE Neurology

A 40-year-old woman with generalised myasthenia gravis has taken azathioprine at a stable dose for 10 months. Her MCV has increased from 90 to 108 fL, but haemoglobin, neutrophils and platelets are unchanged; liver tests are normal and she is well. Which is the most appropriate interpretation and action?

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Correct answer: E — Check other causes of macrocytosis but continue FBC surveillance if no cytopenia is present

Azathioprine can cause a reversible increase in MCV. Isolated macrocytosis does not itself prove efficacy or toxicity, so concurrent causes such as B12 or folate deficiency should be considered while FBC monitoring continues. Myelotoxicity is suggested by leucopenia, thrombocytopenia or pancytopenia, which would require urgent reassessment. Dose escalation based on MCV, automatic B12 treatment, and abandonment of monitoring are unsafe.

Reference: Azathioprine Summary of Product Characteristics: https://www.medicines.org.uk/emc/product/14296/smpc