October 27th, 2011
The Art of Arriving at a Diagnosis
John E Brush, MD
A 55-year-old man came to the emergency room complaining of aching chest pain radiating to the back. The pain had started the day before and recurred several times. It seemed to worsen with exertion and resolve with rest. One resting episode was associated with diaphoresis. Exam, EKG, and cardiac enzymes were normal. A portable chest X-ray showed a slightly widened mediastinum. The ER resident ordered a CT scan of the chest, and the preliminary report was negative for aortic dissection but showed a small pericardial effusion. The patient was placed on aspirin, a beta-blocker, and heparin. A cardiology consultation was called, for presumed unstable angina.
I was on call and saw the patient that Saturday afternoon. After talking with him, I began to question the preliminary CT scan report. I asked an attending radiologist to go over the scan with me, and on careful review, a subtle dissection was noted. The heparin was stopped, and the patient underwent emergency aortic repair. The ER resident was stunned.
“What caused you to doubt the preliminary CT scan report?” he asked. “How did you know?”
“The scan result just didn’t fit,” I said.
Had I simply made a lucky guess? Perhaps. But after eliciting a history, examining the patient, and going over the other details, I formed a mental picture of the case that made me question the preliminary CT scan report.
How do experienced doctors “see” a diagnosis and start to solve a diagnostic problem? How do we begin to generate the “early hypotheses” that I discussed in my previous post? The answer, in my view, lies in pattern recognition.
The Way We Detect Patterns
During the first two years of medical school, we learn about causal reasoning — how basic biologic defects manifest in disease. Unfortunately, patients don’t come to us with an orderly textbook description of a condition. They present with signs and symptoms, forcing us to work backward in seeking a diagnosis. The philosopher Charles S. Peirce described this abductive reasoning as “regressing from a consequent to a hypothetical antecedent.” To begin to work backward, we have to recognize a pattern. The pattern may not be clear initially, or it may lack some key parts — but eventually one does emerge, and it starts us on the path of diagnostic evaluation.
Pattern recognition reinforces two traditional methods in medical practice: the use of narrative and the differential diagnosis. Kathryn Montgomery discusses the use of narrative in her book How Doctors Think. While in training, we physicians present cases repeatedly, practicing the art of developing stories that have meaning. The narratives are detailed, chronological, and structured by events. As we develop a narrative, we set ourselves up to detect patterns.
Judith Bowen has discussed how we transform the details of a patient’s case into a mental abstraction called a “problem representation” (N Engl J Med 2006; 355:2217). I like to think of this transformative step as being similar to solving an algebraic equation — sorting, factoring, canceling, and simplifying. The process starts with active listening, and it requires attentiveness and cognitive energy. We then compare the problem representation with “illness scripts” that are stored in our memory from past clinical decision-making experiences. When we find a match, we have a hypothesis or plausible conjecture that we test (usually against imaging or blood-test results) to work toward a final diagnosis.
But this process has its pitfalls. One is called post hoc, ergo propter hoc — a Latin phrase that describes the faulty assumption that temporal sequence implies causation. Another trap is confirmation bias, or selective use of facts to conform to a desired story. A third trap is anchoring, or placing too much weight on a particular aspect of a story. As we draw inferences from a particular case to arrive at a general principle or conclusion (i.e., as we reason abductively), we must of course avoid hasty generalizations or overgeneralizations. That’s where our training in differential diagnosis comes into play — it helps us entertain alternative diagnoses so that we don’t leap to erroneous conclusions.
Reflecting on how we think, how we generate hypotheses, and how we test them makes us more mindful about the art of arriving at a final diagnosis. In this era of imaging and biomarkers, do we need these diagnostic reasoning skills as much as we once did? To what extent has the art of diagnostic reasoning changed because of our new tools and tests?
13 Responses to “The Art of Arriving at a Diagnosis”
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John, you present a most intriguing case.
I think we have all seen the “missed aortic dissection” by now – often with catastrophic consequences for the patient (I recall one very sad case misdiagnosed and treated with enoxaparin who decompensated and did not make it out of the OR).
Question – and more for my own curiosity – was the preliminary CT interpretation provided on call by a radiology resident or a radiology consultant? Radiologists also engage in this process of pattern recognition. If it was a radiology resident then it would be ironic that the case was misdiagnosed by both an ER resident followed by a radiology resident – but I have actually seen this sequence of “multiplication of errors” many times.
Another note – it can be very hard to start all over again when a case has been handed over to you as a solid “fait accompli” diagnosis (in this case, acute coronary syndrome). One literally has to ignore all the information provided by the referring physician and start again, clearing your mind of any a priori bias. Sounds like you not only worked backwards on this case (as you mentioned) – you also worked forwards (by starting over again with a history, physical examination and then re-examination of the films with an attending radiologist).
A final note: atypical features which do not “fit” with the presumed diagnosis, in this case a widened mediastinum, a pericardial effusion and a history of pain radiating to the back, mandate that one constantly question the working diagnosis, particularly when a catastrophic alternative needs to be excluded and the attendant consequences to the patient are so high.
Dan,
You raise some very good points.
This case occurred several years ago now. As I recall, the initial read was from a resident. But for me, as a cardiologist, the take-away message of the case related to the cognitive pattern recognition that led to questioning the preliminary report. I’m sure the radiology department used this case to demonstrate a very different take-away message about image interpretation and reporting.
As you point out, we could have become “anchored” to the erroneous report, causing us to miss the diagnosis. I suspect that all of us have had similar experiences, where being alert and mindful helped us avoid a serious error. I think it’s fascinating how the mind works, enabling us to reason through clinical problems like this one each and every day.
Thanks for your comments.
John, no doubt this resident (perhaps already an ER attending) will now suffer from availability bias – meaning that every case of chest pain he sees in the ER is deemed a potential aortic dissection that must be ruled out, investigated, worked up. The same bias occurs often in therapy too — if the last patient I treated with warfarin developed an intracerebral bleed, I might be very cautious about applying warfarin in the future, particularly in low to intermediate risk patients. This availability bias has actually been documented in the literature by Choudhry et al in BMJ (and it’s particularly unfortunate, because the last bleed you see has nothing to do with the evidence base favoring (or disfavoring) an intervention – it’s purely a cognitive bias):
BMJ. 2006 Jan 21;332(7534):141-5. Epub 2006 Jan 10.
Impact of adverse events on prescribing warfarin in patients with atrial fibrillation: matched pair analysis.
Choudhry NK, Anderson GM, Laupacis A, Ross-Degnan D, Normand SL, Soumerai SB.
Abstract
OBJECTIVES:
To quantify the influence of physicians’ experiences of adverse events in patients with atrial fibrillation who were taking warfarin.
DESIGN:
Population based, matched pair before and after analysis.
SETTING:
Database study in Ontario, Canada.
PARTICIPANTS:
The physicians of patients with atrial fibrillation admitted to hospital for adverse events (major haemorrhage while taking warfarin and thromboembolic strokes while not taking warfarin). Pairs of other patients with atrial fibrillation treated by the same physicians were selected.
MAIN OUTCOME MEASURES:
Odds of receiving warfarin by matched pairs of a given physician’s patients (one treated after and one treated before the event) were compared, with adjustment for stroke and bleeding risk factors that might also influence warfarin use. The odds of prescriptions for angiotensin converting enzyme (ACE) inhibitor before and after the event was assessed as a neutral control.
RESULTS:
For the 530 physicians who had a patient with an adverse bleeding event (exposure) and who treated other patients with atrial fibrillation during the 90 days before and the 90 days after the exposure, the odds of prescribing warfarin was 21% lower for patients after the exposure (adjusted odds ratio 0.79, 95% confidence interval 0.62 to 1.00). Greater reductions in warfarin prescribing were found in analyses with patients for whom more time had elapsed between the physician’s exposure and the patient’s treatment. There were no significant changes in warfarin prescribing after a physician had a patient who had a stroke while not on warfarin or in the prescribing of ACE inhibitors by physicians who had patients with either bleeding events or strokes.
CONCLUSIONS:
A physician’s experience with bleeding events associated with warfarin can influence prescribing warfarin. Adverse events that are possibly associated with underuse of warfarin may not affect subsequent prescribing.
I think this is an excellent example of why clinical reasoning and judgement based on sound clinical experience is far more important than relying blindly on investigation results and imaging studies which do not conform to the working clinical diagnosis !
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We need diagnostic skills more than ever, but not for the same reasons than before.
What we must be able to do, is to judge adequately before using imaging and biological tools.
Especially because the clinical performance (PPV & NPV) of these tools depends on the prevalence in the population in which we use them.
Great vignette loaded with teaching points. One that jumped out at me was your statement that ” after talking with him” (the patient), you began to question the diagnosis made by others. I suspect that you were the first to elicit a detailed history and really listen to the patient. On teaching rounds, I am routinely horrified by oral presentations that merely state the chief complaint followed by a reading of the radiologist’s report of CT test (images that are rarely scrutinized by the ordering physician). I fear that as a profession we are seeing the demise of of our most valuable tool, the art and skill of history building. Another barrier to improving our skill in pattern recognition is the lack of continuity of care that routinely occurs today in training centers due to compliance with non evidence-based regulations from the RRC. By the way, was there any discrepancies in the arm or leg blood pressures?
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None
Thank you for your great comments.
I think that learning about cognitive psychology reinforces many of the traditions of medicine that we were taught. These traditions evolved and became part of practice because they are useful. Understanding the psychology helps me appreciate the importance of a careful history and review of systems. I wish I had been aware of these principles of cognitive psychology earlier in my career. And I agree that the art seems to be lost in favor of slavishly ordering troponins, BNPs and scans. But you just can’t automate good clinical judgement.
The continuity of care issue is also a problem in private practice. Continuity of care is critically important, yet we are giving it up in an effort to gain efficiency, through-put, etc.
BTW, my patient’s pulses were equal throught.
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My old mentor used to say that “A good clinician can sniff out the diagnosis from the foot of the bed.” I think he was referring to “pattern recognition”. See enough permutations and combinations of same problem, and, as you said, the story just won’t fit with the imaging.
We have got to get back to the old fashioned history and physician supplemented by a (small) modicum of labs and imaging, rather than the omnipresent scattershot approach being used today.
Unfortunately, residents and medical students just haven’t seen enough clinical material to “sniff out the diagnosis from the foot of the bed.” The tendency is to start with the labs and imaging and work our way backwards with a very selective history and physical exam – confirmation bias. While this saves time, rare, catastrophic and unusual diagnoses will inevitably be missed. Thank you for sharing this wonderful case – it should be posted on the wall in every ward and clinic.
This situation is exactly what I’m confronted to in my everyday practice. It’s comforting to read such a clever analysis of the process of medical reasoning without relying blindly to imaging and labs.
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Good case and wonderful analysis of “how we think” (or should I say how we should think). In addition the commentaries are enlightening. Without diverging from the main and very important points made, I did want to reply to this, ” ….Pattern recognition reinforces two traditional methods in medical practice: the use of narrative and the differential diagnosis”.
I think the use of the narrative is going the way of high-buckle shoes. In the days when I could actually dictate an H&P or a consult, I could describe in detail (with flourishes at times!) the patient’s symptom complex and chief complaint. Now however with the use of the EHR we are limited by drop-box menus or our typing skills. I am discouraged from describing in two or even five paragraphs how a patient suffered a syncopal episode or how the current chest pain is different from the chest pain that preceded their prior MI.
The vast majority of diagnosis is in the history obtained from the patient, I think we should strive to convey that narrative the best we can.
I agree. The electronic medical record forces physicians to type a condensed HPI, which often saps meaning out of the narrative.
An EMR has many advantages, and imaging can be very useful. We just have to learn how to incorporate these technologies into our thought processes, rather than struggling to accomodate our thought processes to the new technologies.
Great posts and comments. I would like to add that many times phyisicians are reluctant to take time to the narrative and to know the detailed history from the patient’s words. Usually this practice delays diagnosis instead of reaching it at the proper time, and what is worst, it adds potential risks to the patient beacause of a misdiagnosis, as in many cases we see daily. I completely agree with Dr Leutkemeyer when he says that maybe you were the first to obtain a detailed history from the patient and to take a real look to the images which rarely are seen, at least in my everyday practice I also notice that most pyhisicians just read reports. Maybe you were the first who took the time the case deserved to understand what was happening to the patient, and time is something that is very scarce in hospitals in general, I think this is one of the main explanations behind histories of this kind.
John- your compulsive approach to scrutinize both subjective and objective elements of the entirety is to be commended. This harkens back to the adage of one of my mentors, Mary Charleson(yes, on the Charleson morbidity index)- “Act on evidence, not on inference”.
To be fair, we who come in the “next day” often have the benefit of the distillation of a bombardment of objective data, which at the sharp point of collection and collation on the part of house staff, is often difficult for the latter to organize and sort through. Also, did you have in your recesses of mindful data storage the pillar of the dissection triad codified by IRAD(International Registry of Aortic Dissection)- tearing chest pain with radiation to back(although tearing not described in your synopsis), widened mediastinum on CXR, pulse deficit(which you latter qualify as not being present) which has a 66% positive predictive value for aortic dissection in present or past hypertensive patient? As to the hypertension element, was this present?