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2018-09-28
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Of Horses, Zebras & Chameleons:Diagnostic Reasoning in EM
Eric Dryver, MD, FEBEMSkåne’s University Hospital, Lund, Sweden
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CURRENT
PREVIOUS
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Zebra/Horse
• Uncommon condition
• Mistaken for common one
• Focus on false positive
Chameleon
• Common condition
• Uncommon presentation
• Focus on false negative
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Stroke Mimics
• Migraine
• Seizure
• Infection
• Psychiatric
• Nausea/vomiting
• Fall
• Vertigo
• Movement disorder
False Positive Stroke Dx False Negative Stroke Dx
Stroke Chameleons
STEMI
Stroke
Infection inthe elderly
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Diagnostic Error: Definition
Failure to:
• establish accurate and timely explanation of the patient’s health problem(s)
or
• communicate that explanation to the patient
ED Perspective
• Forefront of process
• Limited information
• Hindsight bias
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"Absolute certainty in diagnosis is unattainable, no matter how muchinformation we gather . . . . Our task is . . . to reduce the level ofdiagnostic uncertainty enough to make optimal therapeutic decisions.”
Jerome Kassirer
”Medicine is a science of uncertainty and an art of probability.”William Osler
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Bayes’ theorem
Pro
babi
lity
Pre-Test Post-Test
Time-Sensitive Diagnoses
• Pulmonary embolism
• Stroke
• Sepsis
• Lung cancer
• Multiple sclerosis
• Rheumatoid arthritis
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Over-Investigation
Test Threshold
Pro
babi
lity
Pre-Test Post-Test
Test Threshold
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Diagnostic Error in EM
• Failure to accuratelyevaluate the likelihoodof time-sensitive conditions based on available information
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Ventricular tachycardia?
Atrial fibrillation+
left bundle branch block?
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Fengler et al. Am J Emerg Med 2007;25:576-583
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Diagnostic Errors: Etiology
System-Related Errors
• Limited time/data
• Multitasking
• Interruptions
• Equipment failure
No-Fault Errors
• Uncooperative patient
Cognitive Errors
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System 1
• Unconscious
• Pattern recognition, coherence
• Jumps to conclusions
• Effortless/Emotional
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System 2
• Conscious
• Analytical
• Rule-based
• Tedious
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Diagnostic Errors: Cognitive Sources
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Diagnostic Errors: Cognitive Sources
”We only see what we know.”
Johann Wolfgang von Goethe
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Diagnostic Errors: Cognitive Sources
Premature Closure
• Fever
• Dyspnea
• Pleuritic chest pain
• WBC, CRP
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Arch et al. Stroke 2016;47:668-73
Faulty Data/Knowledge/Interpretation?
"The root cause of diagnostic error is difficult to study as errorstend to be defined only in hindsight and the ‘microscope’ that canenable detection of mental processes in live time has yet to be invented.”
Geoffrey Norman
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STEMI?
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FaultyInterpretation
FaultyData
FaultyKnowledge
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Reducing Diagnostic Error Risk
Cognitive Debiasing
• Be aware of your biases
• Apply counter-strategy
Lack of Evidence• Sherbino et al. Teach Learn Med 2011;23:78-84
• Shimizu et al. Med Teach 2013;35:e1218-29
• Sherbino et al. CJEM 2014;16:34-40
• Norman et al. Acad Med 2014;89:277-84
• Smith et al. Diagnosis 2015;2:117-121
Theoretical Concerns
• Which of the 38+ biases?
• Risk of over-investigation
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0 - 1 - 2
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0 - 1 - 2
Time-Sensitive
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Freund Y et al. JAMA Internal Medicine 2018;178:812-9
Redo table
Scenario-Based Classroom Training
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Emergency Medicine Core Competences
• Take EMCC
• Teach EMCC
• Direct EMCC locally
• Run local scenarios
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Take-Home
