Logical commentary:
How does the clinician limit her differential diagnoses? What criteria
does she use to narrow the hypothetical diagnostic space? The clinician
will look carefully for features in the patient’s history, perform a
physical examination, and pursue initial testing. Some details will be
retained; others rejected or held in abeyance. She will listen to tone
of voice; try to assess anxiety bearing in mind that the patient has
received heretofore 30 mg of morphine. She will examine not only
quantitatively but also qualitatively—observe the state of the
manifestation of his pain, anxiety, and the look in his eyes. She must
proceed with a rapid assessment to rule out referred pain—e.g. from
acute pancreatitis, from another abdominal organ. Some of her
observations are salient at the time of the first examination. It is not
uncommon for some physicians, in certain clinical circumstances, to
delay an hour or more before an acute abdomen diagnosis is firmly
established by re-examination. But in this case there is no time to
delay, as the pain seems to be continuous even with morphine analgesia.
Some of the observations fit into a picture of myocardial damage, others
do not fit.
The emphasis must be on reforming the observations into an emerging,
bringing-into-focus picture, on filling in the pieces as expeditiously
as possible to include less common conditions, even redundantly
reviewing the initial observations so as not to overlook subtle
clues—e.g. persistent 7/10 chest pain partially relieved by higher and
more frequent narcotic administrations and a soft holosystolic murmur
across the precordium.
In the case at hand the physician is faced with conflicting observations
and testing that is equivocal. Although the history of non-exertional
chest pain seems counter-intuitive for stress-induced coronary artery
disease, the negative enzyme measurements and ECG tracings should be
evidence against the diagnosis of cardiac injury.
But there is strong clinical and epidemiologic background information
from population studies and clinical disease presentations that are
atypical and do not fit the textbook picture based on the population
under consideration. Despite the negative tests, the suspicion (prior
probability) of cardiac injury is high enough to persist in testing the
clinical presentation with routine tests or even to perform angiography
or tests to show calcification of the coronary arterial system.
The clinician must not miss the commonest diagnosis; she must not
prematurely close the consideration of hypotheses. Perhaps the
presenting picture needs refocusing and another observer must review the
data? This may be prudent as the case develops in atypical fashion i.e.
borderline enzymes, ECG non-diagnostic, pain relief minimal. At the same
time, she must not miss a life-threatening condition either. The
standard protocol calls for repeating cardiac enzymes; and it is
standard practice to continue to monitor the ECG and to observe the
patient closely for signs of decompensation, while at the same time
reviewing the differential diagnoses so not to miss or confuse this case
with another lookalike disease, a mimic of cardiac injury. If the
physician were working in or with another situation where prevalence
would differ, the list of probable diagnoses might change—e.g. in
South America she would need to consider Chagas disease, uncommon in the
U.S.A.
Now the work of the physician is to complete, as well as she can, the
picture of the specific etiology of chest pain. She may need to repeat
the initial tests, review the clinical history, and hypothesize other
explanations in a timely fashion. This is another challenge. She may
call for another pair of eyes; sometimes this is a fallback position,
other times it grows out of being confused by the picture or even
dissatisfaction with her own thought process. She may doubt her
diagnostic considerations and require additional testing to secure an
accelerated pathway to a more assured diagnosis. This is common
especially during training.
Saliency emerges based on experience—i.e. recall of the association of
clinical findings (history of non-exertional chest pain, negative
enzymes and ECG, continuing pain relieved only with narcotics) with
previous disease states. She chooses those features that functioned in
the past to anticipate an outcome—a diagnosis. Discrimination based on
previous experience gives her the ability to create a full picture and
to recognize that this clinical picture resembles, in all or most of the
details, pictures she has seen before. This may be called pattern
recognition. Patterns that clarify the way to proceed towards diagnosis
selection and treatment emerge from experience. In short, successful
diagnosis requires careful, judicious, and experienced observation for
pattern recognition.11For an exposition of how this process
works semiotically—that is, by the creation of mental signs such as
pictures, diagrams, schematta, and so on—see Silveira 2005.