uk-dgm MCQ (SBA): Statin-Induced Myopathy

A 73-year-old woman presents with a 4-month history of progressive bilateral leg weakness, fatigue, and difficulty rising from a chair. She has been on Atorvastatin 80 mg for 2 years. Examination reveals proximal muscle weakness (MRC grade 4/5) in the hip flexors and shoulder abductors bilaterally. CK is mildly elevated at 580 U/L (normal <200). What is the MOST likely cause of her symptoms?