He warned of mimics and chameleons. For example the conditions that mimic stroke are migraines, seizures, infections and psychiatric conditions, which can lead to false positive stroke diagnoses. False negative stroke diagnoses can arise from stroke chameleons — nausea/vomiting, falls, vertigo and movement disorders. One study found that misdiagnosis occurred both in a community hospital and an academic teaching hospital. 22% of strokes were initially misdiagnosed.
The Zebra/horse dyad refers to uncommon conditions that can be mistaken for common ones with a focus on false positive. Chameleons are common conditions with uncommon presentations with focus on false negative.
What leads to diagnostic error in the emergency department?
There are system-related errors, due to limited time and/or data, multi-tasking, interruptions and equipment failure. There are cognitive errors on the part of the physician and also no-fault errors, such as an uncooperative patient. There may be insufficient data or that doctors only see what they know. Data can be interpreted in different ways (premature closure).
“The root cause of diagnostic error is difficult to study as errors tend to be defined only in hindsight and the ‘microscope’ that can enable detection of mental processes in live time has yet to be invented”—Geoffrey Norman. Professor of Clinical Epidemiology & Biostatistics, McMaster University
In the emergency department at Lund they have symptom checklists, e.g. for chest/thoracic pain - these cover background information to be collected, history, physical examination and tests with suggested diagnoses. These are available on the lucem (clarity in emergency medicine) website.
Dryver cited anonymous internal medicine dogma: “when you hear hoofbeats, think horses, not zebras” and Kline’s dogma collar “If you don’t know what a zebra looks like, good luck putting a saddle on that ‘horse’.
And he recommended reading Effect of Systematic Physician Cross-checking on Reducing Adverse Events in the Emergency Department: The CHARMED Cluster Randomized Trial.