Clinical reasoning errors
Traps for the unwary - common reasoning mistakes made by junior residents
- Not accounting for the patient's unique vocabulary in determining what
is being said e.g. 'dizzy' meaning lightheaded and not vertigo, 'sudden'
meaning occurred today versus abrupt and severe,
- Leading the patient e.g. 'so the pain was crampy?' when the patient
meant fluctuating in intensity
- Not identifying a major change in the chronology of the illness and
symptoms particularly when there is an acute deterioration (e.g. ischaemic
stroke with haemorrhagic transformation)
- Not maintaining a broad enough differential diagnosis
- Moving on to an investigation strategy before even thinking about the
differential diagnosis
- Ordering tests but not anticipating what to do with unexpected results
- Seizing upon the first possibility that matches the clinical information
and taking a cursory history (see The Eureka Syndrome)
- Not looking for a plausible cause for the patient's condition (e.g.
'food poisoning' despite sharing the same food as other asymptomatic people)
An inadequate understanding of pathophysiology or disordered anatomy and
symptomatology e.g. syncope due to TIA
- Not treating the cause (e.g. transfusion for anaemia but not treating
the slowly bleeding ulcer)
- Not making a proper assessment of the severity of the condition
resulting in delayed treatment or incorrect disposition (e.g. asthma
imminently going into respiratory failure)
- Not reacting promptly when there is a change in the patient's condition
or inadequate response to treatment (e.g. hypotension following GTN infusion
for ACS - ?cardiogenic shock)
- Assuming there is only one problem going on when there may be multiple
(e.g. CCF and COAD)
"You see only what you look for; you recognise only what you know"
- This quote from the famous neuroradiologist Merrill Sosman is equally
applicable to clinical reasoning as it is to radio-diagnosis.
- Several reasoning errors are commonly committed by even experienced
clinicians. The most common one goes along these lines.....
"When you hear hoofbeats. I think horses" - In many cases this is true but
occasionally you will meet a zebra. Often there are features that suggest
it isn't a horse but the clinician neglects to make a search for these and
terminates the assessment and analysis (premature closure).
- On the other hand, the novice clinician sees zebras everywhere; lacking
an intimate knowledge of the range of diagnostic possibilities or the
practical experience to recognise common disease patterns.
- Both of these errors reflect a haphazard system of approaching an
undifferentiated complaint.
- An example is a patient who presents with upper abdominal pain and the
doctor only considers GIT causes and not cardiac or respiratory ones. The
prudent historian will ensure that such situations she would include a
screening cardiac and respiratory assessment to identify this possibility.
- A solid grounding in pathophysiological mechanisms and anatomical
relationships goes a long way to developing a systematic and meticulous
approach to the diagnostic process.
The Eureka syndrome
Premature termination of search for information (premature closure) is one
of the commonest causes of misdiagnosis.
Finalising a hypothesis should not occur just because a few symptoms are
consistent with the proposed condition.
To avoid error follow these steps........
- Is the epidemiology of the disease consistent with the age, sex and
demographics of the patient e.g. Tertiary syphilis in a 25 year Western
European native.
- Is the time course of the symptoms consistent with the known
pathogenesis and natural history of the condition (see The chronology
suggests the pathology) e.g. 2 months of occasional PR bleeding - ?acute
food poisoning
- Is the time course of the clinical data consistent with a known
complication of the disease e.g. New ST elevation 3 days post MI -
?ventricular aneurysm
- Does the patient possess known risk factors for acquiring the disease
e.g. Aortic aneurysm in a young person with no history of hyperlipidaemia,
diabetes, smoking, hypertension or family history of vascular disease
- Are the physical findings and investigations consistent with the
diagnosis e.g. pericardial rub and normal cardiac enzymes in acute MI
- Can the clinical features be equally explained by an alternative
diagnosis e.g. pleurisy vs pulmonary embolus
- Does any of the clinical information contradict what is known about the
disease e.g. normal lung function tests and emphysema
- Is the condition responding to the treatment in the time frame that is
expected e.g. no response to a course of antibiotics for 'ear infection'
- Can all of the observations be explained in mechanistic fashion (i.e.
deranged anatomy and physiology, homeostatic compensatory mechanisms,
progression of disease, symptoms and signs, investigation results, response
to treatment) e.g. massively swollen leg with normal leg ultrasound - ?small
non-visible clot
Hint - each of these examples contain contradictory information