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Bullous Pemphigoid — SCE Dermatology MCQ

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EasyDermatopharmacologyBullous PemphigoidSCE Dermatology

A 60-year-old woman on long-term Azathioprine for pemphigoid is found to have a significantly low TPMT activity (homozygous deficient). What is the immediate management?

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Correct answer: B — Stop Azathioprine immediately

Thiopurine methyltransferase (TPMT) deficiency (homozygous, prevalence ~0.3%) results in accumulation of cytotoxic 6-thioguanine nucleotides, causing severe life-threatening myelosuppression (pancytopenia). Azathioprine must be stopped immediately in homozygous TPMT-deficient patients. TPMT testing should ideally be performed BEFORE starting Azathioprine. Heterozygous patients (intermediate TPMT, ~10% prevalence) require dose reduction (typically 50%). Alternative immunosuppressants (Mycophenolate mofetil, Methotrexate) should be considered. BAD guidelines mandate TPMT testing prior to Azathioprine initiation.

Reference: BAD 2018 Drug Monitoring Guidelines; BNF