MSRA-2370

A 65-year-old woman with type 2 diabetes is found to have an elevated plasma creatinine of 150 μmol/l (reference range 62–106 μmol/l). Her blood pressure is 170/95 mmHg, and fundoscopy reveals mild hypertensive changes and background diabetic retinopathy. She has a neuroischaemic ulcer on her left foot and no palpable pedal pulses. Urine dipstick is negative, and renal ultrasound shows a 8.5-cm left kidney and a 6.2-cm right kidney, with reduced cortical thickness.
What is the most likely cause of the renal impairment?