Mythmaking in medical education and medical practice.

Background: Despite the emergence of evidence-based medicine, gaps in medical knowledge are filled by tradition, common sense, and experience, giving rise to medical myths.

Methods: We explored the origins of and evidence related to four medical myths: patients with shellfish allergies should not receive intravenous contrast, patients with atrial fibrillation of less than 48 hours' duration do not require anticoagulation before cardioversion, patients with suspected meningitis should have a computed tomography (CT) scan before a lumbar puncture, and patients with respiratory disease should not receive β-blockers. We conducted a literature review to describe each myth's origins and the quality of supporting evidence.

Results: All patients with allergies, including but not limited to seafood allergies, are at an increased risk for anaphylactoid reactions to radiocontrast. No conclusive studies indicate that patients with atrial fibrillation of less than 48 hours' duration do not require anticoagulation before cardioversion. A CT scan before lumbar puncture in suspected acute bacterial meningitis is a clinically inefficient precaution. β-blockers can be safely used in patients with respiratory disease and may even prevent cardiac events in these patients.

Conclusions: These familiar myths have maintained prominent roles in medical thinking because they represent wisdom passed down from eminent sources, they teach physiology and medical skills, and they offer physicians a sense of control in the face of uncertainty. In addition to providing scientific evidence, changing physicians' practice requires acknowledging that even meticulous care cannot always avert bad outcomes.