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AED-Induced Osteoporosis — SCE Neurology MCQ

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ModerateEpilepsy & Seizure DisordersAED-Induced OsteoporosisSCE Neurology

A 60-year-old man with known epilepsy on long-term phenytoin and carbamazepine presents with back pain and a DEXA scan showing a T-score of −2.8 at the lumbar spine. What is the relationship between his antiseizure medications and bone health?

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Correct answer: C — Enzyme-inducing AEDs (phenytoin, carbamazepine) increase vitamin D metabolism via CYP450 induction, contributing to reduced bone mineral density and increased fracture risk

Enzyme-inducing AEDs (phenytoin, carbamazepine, phenobarbital) increase CYP450 activity, accelerating the metabolism of vitamin D to inactive metabolites. This leads to reduced calcium absorption, secondary hyperparathyroidism, reduced bone mineral density, and increased fracture risk. NICE NG217 recommends assessing bone health in patients on long-term enzyme-inducing AEDs. Vitamin D supplementation, DEXA screening, and consideration of switching to non-enzyme-inducing AEDs are recommended. A: There is a well-established relationship. C: AEDs do not protect bone. D: Non-enzyme-inducing AEDs may also affect bone through different mechanisms. E: Bone loss begins much earlier.

Reference: NICE NG217 (2025); BNF; ABN Epilepsy Guidelines