Renal Infarct: Expanding the Differential Diagnosis in Flank Pain Presentations

Flank pain is a common emergency presentation and common pitfall is premature closure, assuming that obstructive nephrolithiasis is the diagnosis; when the unenhanced CT KUB is negative – the flank pain often gets diagnosed as “MSK flank pain” which has a similar clinical picture of sudden onset flank pain that resolves over days. In patients with sudden flank pain whom unenhanced CT is negative for nephrolithiasis, and alternate diagnoses such as leaking AAA, aortic dissection, pulmonary embolism, spinal pathology etc. have been ruled out, renal infarct should be suspected.

Why do we care about renal infarct? Secondary prevention! Most are thromboembolic in origin. It is important to identify the cause, such as atrial fibrillation. Missing a renal infarct may be a missed opportunity to start patients on anticoagulation for stroke prevention. The clinical presentation of renal infarct can be thought of as “the mesenteric ischemia of flank pain”: unexplained severe flank pain in patients with a history of atrial fibrillation should be thought of similarly to unexplained severe abdominal pain in patients with a history of atrial fibrillation, in whom mesenteric ischemia should be considered.

The incidence of renal infarct is 1.4% in the general population and 2% in those with atrial fibrillation. Risk Factors to increase pre-test probability of renal infarction include:

• • Autoimmune disorders
  • Cardiovascular risk factors
  • Connective tissue disorders such as Marfan’s Syndrome
  • Hypercoagulable states such as malignancy
  • Endocarditis
  • History of atrial fibrillation
  • Active or recent infection

Work-up if renal infarct is suspected: the majority of acute renal infarcts (91%) will have isolated Lactate Dehydrogenase (LDH) elevation without evidence of hemolysis or elevation in other transaminases, and a definitive diagnosis can be made with contrast-enhanced abdominal CT. Work up outside of the ED should include an echo, Holter monitor, and a hypercoagulability workup.

=>Bottom line: Renal Infarct should be on your differential diagnosis, and consideration of a screening LDH done, for patients who present with renal colic and have a normal unenhanced CT, because most of these will be thromboembolic. If you identify the renal infarct from this cause and anticoagulate them, you could prevent a stroke.

The Podcast: EM Quick Hits 50 Normal Unenhanced CT Renal Colic DDx, Perichondritis, Magnesium in Pediatric Asthma, Steroids for Pneumonia, Chest Pain ECG

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