Question

During morning rounds, a hospital medicine team evaluates a 68-year-old male with acute kidney injury. The patient underwent coronary angiography with drug-eluting stent placement two weeks prior for unstable angina. At that time, his baseline serum creatinine was $1.0\text{ mg/dL}$, which has steadily increased to $3.5\text{ mg/dL}$ over the past three days. He reports vague lower extremity pain. Physical examination reveals a reticular, purplish discoloration over his bilateral toes and soles. Laboratory testing shows a peripheral blood eosinophilia of $8\%$. Urinalysis demonstrates $1+$ proteinuria with $5$ to $10$ white blood cells per high-power field, some of which are identified as eosinophils. To clarify the diagnosis, a percutaneous renal biopsy is performed. Light microscopy of the biopsy specimen reveals small and medium-sized muscular arteries with lumens partially occluded by biconvex, needle-shaped empty spaces. These clear spaces are surrounded by an accumulation of multinucleated giant cells and a fibrotic intimal reaction. The glomerular tufts are ischemic but otherwise unremarkable. Based on the biopsy findings and clinical presentation, which of the following is the most likely diagnosis?