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Thrombolysis Contraindication – Recent Haemorrhage — SCE Neurology MCQ

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HardCerebrovascular DiseaseThrombolysis Contraindication – Recent HaemorrhageSCE Neurology

A 21-year-old with heavy nitrous-oxide exposure develops sensory ataxia, distal weakness and dorsal-column cervical MRI signal. Haemoglobin, MCV and serum B12 are normal. Which next diagnostic and treatment step is most appropriate?

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

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Correct answer: B — Check methylmalonic acid or homocysteine and give intramuscular cobalamin after stopping nitrous oxide

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

A is wrong because nitrous oxide functionally inactivates cobalamin and serum B12 may remain normal. B delays treatment until a haematological feature that may never appear and continued exposure prevents recovery. C is correct: raised methylmalonic acid or homocysteine demonstrates functional B12 deficiency; intramuscular B12 should start promptly and abstinence is essential. D risks misdiagnosing a toxic myeloneuropathy as GBS. E does not reverse cobalamin inactivation and can obscure haematological deficiency without treating neurological disease.

Reference: Nitrous oxide-induced subacute combined degeneration: diagnosis and treatment: https://pn.bmj.com/content/23/3/222