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Allopurinol SJS – Temporal Relationship — SCE Neurology MCQ

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HardEpilepsy & Seizure DisordersAllopurinol SJS – Temporal RelationshipSCE Neurology

A 55-year-old man with known epilepsy on carbamazepine develops a painful skin rash 3 weeks after starting allopurinol for gout. The rash has mucosal involvement and he has systemic symptoms (fever, malaise). What is the most likely drug responsible?

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Correct answer: E — Allopurinol — this is the most common cause of SJS/TEN overall, and the temporal relationship (3 weeks after initiation) confirms it as the causative agent rather than carbamazepine (which he has been on for years)

While carbamazepine is a well-known cause of SJS/TEN, this patient has been on it for years without reaction. Allopurinol is the most common overall cause of SJS/TEN and was recently introduced (3 weeks ago — within the typical 1–8 week window for drug-induced SJS). The temporal relationship to allopurinol initiation makes it the most likely causative agent. Both carbamazepine and allopurinol share cross-reactivity through the HLA-B*58:01 allele. Management: stop allopurinol immediately. A: CBZ has been tolerated for years. C: Temporal relationship favours allopurinol. D: Drug cause is likely. E: Viral infection is less likely with the temporal drug relationship.

Reference: BAD SJS/TEN Guidelines; BNF