A patient develops a blue toe after cardiac catheterization, with rising creatinine and BUN. The most likely diagnosis is:

• A. Acute tubular necrosis from contrast
• B. Thromboembolism to the toe
• C. Cholesterol embolization to the kidneys without eosinophils
• D. Atheroembolism to renal circulation with eosinophiluria

Answer: (D)

Cholesterol crystal embolization from atherosclerotic plaques after vascular procedures is the driving idea. When catheters scrape along the aorta, cholesterol crystals can shower into small arteries, lodging in skin and kidney arterioles. This produces a blue toe or livedo reticularis from digital ischemia and an acute kidney injury as the microvasculature in the kidneys is blocked. The inflammatory response to these crystal emboli often includes eosinophils, which can appear in the urine as eosinophiluria and help confirm the diagnosis. So, the combination of a recent vascular procedure, a blue or mottled toe, rising BUN and creatinine, and eosinophiluria fits best with atheroembolism to the renal circulation with eosinophiluria.

Contrast-induced acute tubular necrosis from the contrast would explain the kidney injury after exposure but not the toe ischemia and typically lacks eosinophiluria. Atheroembolism to the kidneys without eosinophils is less likely given the eosinophiluria. A thromboembolism to the toe explains the limb findings but not the concurrent renal injury with eosinophilia.