25th July 2023

A 68-year-old lady with well controlled epilepsy presents with bone pain in her lower limbs and muscle weakness.

A 68-year-old lady with well controlled epilepsy presents with bone pain in her lower limbs and muscle weakness. She has been taking phenytoin for the past 20 years with good effect. As she was stable, she was left on this by the neurologist, with close monitoring for side effects. On examination, she was also noted to have a waddling gait. She was found to have a Vitamin D level of 12, and thus diagnosed with osteomalacia.

What is the likely cause of this patient’s osteomalacia?

Select the SINGLE most appropriate option from the list below. Select ONE option only.