Question

A 68-year-old man with hypertension and coronary artery disease undergoes percutaneous coronary intervention (PCI) for unstable angina. Two weeks later, he presents with fatigue, worsening renal function (creatinine 3.1 mg/dL from baseline 1.2 mg/dL), eosinophilia, and a serpiginous, mottled rash over both legs. Which of the following is the most likely diagnosis?

• A. Acute tubular necrosis
• B. Contrast-induced nephropathy
• C. Cholesterol crystal embolism
• D. Acute interstitial nephritis

Hint:

Differentiating post-cath AKI:
Contrast Nephropathy: Onset within 24-48 hours. Usually recovers in a week. No systemic signs.
Cholesterol Embolism: Onset delayed (1-2 weeks). Cutaneous signs (livedo reticularis, blue toes), Eosinophilia, Hypocomplementemia. Prognosis is generally poor.

Answer 1

The Correct Option is C

Concept:
The clinical picture involves an elderly man with severe vascular disease who underwent an endovascular procedure (PCI) and subsequently developed a delayed Acute Kidney Injury (AKI) combined with systemic and cutaneous findings.
This triad is the hallmark of atheroembolic renal disease (cholesterol crystal embolism).
Explanation:
• During catheter-based vascular interventions like coronary angiography or PCI, catheters inevitably scrape the walls of the aorta.

• In patients with severe atherosclerosis, this mechanical trauma can dislodge fragments of cholesterol-rich atherosclerotic plaques.

• These microscopic cholesterol crystals embolize downstream, lodging in small arterioles in various organs, most notably the kidneys, skin, and gastrointestinal tract.

• The crystals trigger a prominent foreign-body macrophage response and inflammatory reaction.

• This delayed inflammatory response explains why the AKI in cholesterol embolism typically manifests 1 to 2 weeks post-procedure, rather than immediately.

• The cutaneous manifestation described as a "serpiginous, mottled rash" is livedo reticularis, resulting from microvascular occlusion in the skin. Embolization to the digits causes "blue toe syndrome".

• The systemic inflammatory response accounts for the characteristic laboratory finding of eosinophilia (and eosinophiluria).

• Option (A), Acute tubular necrosis (ATN), typically results from profound ischemia or toxins but does not produce livedo reticularis or eosinophilia.

• Option (B), Contrast-induced nephropathy (CIN), also occurs post-PCI but exhibits a completely different timeline. CIN occurs acutely within 24 to 48 hours of contrast administration and rapidly peaks within 3 to 5 days. It does not cause cutaneous lesions or eosinophilia.

• Option (D), Acute interstitial nephritis (AIN), could cause AKI and eosinophilia (usually drug-induced, e.g., NSAIDs or antibiotics), but it does not cause livedo reticularis.
Final answer:
The combination of a recent endovascular procedure, delayed AKI, eosinophilia, and livedo reticularis is diagnostic of Cholesterol crystal embolism.