History:

A 64-year-old male presents with a 4-month history of progressively worsening generalized weakness and fatigue. He has recently developed decreased urine output. There is no history of diabetes mellitus or hypertension. Laboratory investigations reveal a serum creatinine of 3.8 mg/dL and blood urea of 95 mg/dL. Urinalysis shows proteinuria of 1.2 g/day with granular casts.