Chronic Cerebral Ischemia: Where “Evidence-Based Medicine” Fails Patients

Abstract

The publication of the COSS (Carotid Occlusion Surgery Study) trial in 2011 concluded that the addition of external carotid to internal carotid (EC-IC) bypass to a medical regimen "did not reduce the risk of ipsilateral ischemic stroke at 2 years" for patients with symptomatic internal carotid artery occlusion. This has resulted in decreasing referrals for surgical management under the guise of "evidence-based" medicine. The conclusions drawn from a study can only be as good as the selected end points. COSS did not consider important end points such as the effects of long-term cerebral ischemia or recurrent debilitating transient ischemic attacks (TIAs). However, the study is often quoted as "proof" that EC-IC bypass has no role in the treatment of these patients. A middle-aged patient presented to a primary neurologist with left-sided weakness and 2 months of personality changes. Magnetic resonance imaging (MRI) showed small watershed infarcts in the right hemisphere. An angiogram showed right carotid occlusion. Perfusion scans confirmed hypoperfusion. The patient was managed medically. Without any further clinical stroke events, the patient progressed to complete hemispheric infarction on MRI over the next 5 months. The public perception of the results of large randomized clinical trials is significantly altered by their ubiquitous dissemination and broad generalization without adequate understanding of the details. Careful assessment of the methodology and end points of a trial are essential when applying the results for evidence-based medicine to individual patients. This patient would have been considered a medical "success" in COSS, but her outcome with surgical intervention will never be known.