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Lamotrigine SJS — MRCPsych Paper B MCQ

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ModerateMood DisordersLamotrigine SJSMRCPsych Paper B

A 48-year-old man with bipolar I disorder is taking valproate. Lamotrigine is added and its dose is increased more rapidly than the recommended schedule. Three weeks later, he develops fever, marked skin pain, dusky macules, flaccid blisters, oral and ocular erosions, and epidermal detachment affecting 12% of his body surface area. Which serious adverse drug reaction is most likely?

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Correct answer: C — Stevens–Johnson syndrome/toxic epidermal necrolysis

The correct answer is Stevens–Johnson syndrome/toxic epidermal necrolysis (SJS/TEN). Early onset after starting lamotrigine, skin pain, dusky lesions, prominent mucosal erosions and epidermal detachment are characteristic. Detachment of 10–30% of body surface area is classified as SJS/TEN overlap. Lamotrigine risk is increased by excessive initial dosing or rapid escalation and by concomitant valproate, which inhibits lamotrigine metabolism. DRESS more typically features facial oedema, eosinophilia and internal-organ involvement. Acute generalised exanthematous pustulosis produces numerous sterile pustules. Bullous pemphigoid usually causes tense, pruritic blisters, while erythema multiforme major classically has raised target lesions with limited detachment. Lamotrigine should be stopped immediately, and it must never be restarted after SJS/TEN.

Reference: Electronic Medicines Compendium, Lamotrigine Milpharm 50 mg tablets, Summary of Product Characteristics, sections 4.2 and 4.4, revised 12 May 2026. https://www.medicines.org.uk/emc/product/4737/smpc