Chapter 003. Decision-Making in Clinical Medicine (Part 2)

The following three examples introduce the subject of clinical reasoning:A 46-year-old man presents to his internist with a chiefcomplaint of hemoptysis. The physician knows that the differential diagnosis of hemoptysis includes over 100 different conditions, including cancer and tuberculosis. The examination begins with some general background questions, and the patient is asked to describe his symptoms and their chronology. By the time the examination is completed, and even before any tests are run, the physician has formulated a working diagnostic hypothesis and planned a series of steps to test it. In an otherwise healthy and nonsmoking patient recovering from...
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Chapter 003. Decision-Making in Clinical Medicine (Part 2) Chapter 003. Decision-Making in Clinical Medicine (Part 2)The following three examples introduce the subject of clinical reasoning:  A 46-year-old man presents to his internist with a chiefcomplaint of hemoptysis. The physician knows that the differentialdiagnosis of hemoptysis includes over 100 different conditions, includingcancer and tuberculosis. The examination begins with some generalbackground questions, and the patient is asked to describe his symptomsand their chronology. By the time the examination is completed, and evenbefore any tests are run, the physician has formulated a working diagnostichypothesis and planned a series of steps to test it. In an otherwise healthyand nonsmoking patient recovering from a viral bronchitis, the doctors hypothesis would be that the acute bronchitis is responsible for the small amount of blood-streaked sputum the patient observed. In this case, a chest x-ray may provide sufficient reassurance that a more serious disorder is not present.  A second 46-year-old patient with the same chief complaint who has a 100-pack-year smoking history, a productive morning cough, and episodes of blood-streaked sputum may generate the principal diagnostic hypothesis of carcinoma of the lung. Consequently, along with the chest x-ray, the physician obtains a sputum cytology examination and refers this patient for fiberoptic bronchoscopy.  A third 46-year-old patient with hemoptysis who is from a developing country is evaluated with an echocardiogram as well, because the physician thinks she hears a soft diastolic rumbling murmur at the apex on cardiac auscultation, suggesting rheumatic mitral stenosis. These three simple vignettes illustrate two aspects of expert clinicalreasoning: (1) the use of cognitive shortcuts as a way to organize the complexunstructured material that is collected in the clinical evaluation, and (2) the use ofdiagnostic hypotheses to consolidate the information and indicate appropriatemanagement steps. The Use of Cognitive Shortcuts Cognitive shortcuts or rules of thumb, sometimes referred to as heuristics,can help solve complex problems, of the sort encountered daily in clinicalmedicine, with great efficiency. Clinicians rely on three basic types of heuristics.When assessing a particular patient, clinicians often weigh the probability that thispatients clinical features match those of the class of patients with the leadingdiagnostic hypotheses being considered. In other words, the clinician is searchingfor the diagnosis for which the patient appears to be a representative example; thiscognitive shortcut is called the representativeness heuristic. It may take only a few characteristics from the history for an expertclinician using the representativeness heuristic to arrive at a sound diagnostichypothesis. For example, an elderly patient with new-onset fever, coughproductive of copious sputum, unilateral pleuritic chest pain, and dyspnea isreadily identified as fitting the pattern for acute pneumonia, probably of bacterialorigin. Evidence of focal pulmonary consolidation on the physical examinationwill increase the clinicians confidence in the diagnosis because it fits the expectedpattern of acute bacterial pneumonia. Knowing this allows the experiencedclinician to conduct an efficient, directed, and therapeutically productive patientevaluation since there may be little else in the history or physical examination ofdirect relevance. The inexperienced medical student or resident, who has not yetlearned the patterns most prevalent in clinical medicine, must work much harder toachieve the same result and is often at risk of missing the important clinicalproblem in a sea of compulsively collected but unhelpful data. However, physicians using the representativeness heuristic can reacherroneous conclusions if they fail to consider the underlying prevalence of twocompeting diagnoses (i.e., the prior, or pretest, probabilities). Consider a patientwith pleuritic chest pain, dyspnea, and a low-grade fever. A clinician mightconsider acute pneumonia and acute pulmonary embolism to be the two leadingdiagnostic alternatives. Using the representativeness heuristic, the clinician mightjudge both diagnostic candidates to be equally likely, although to do so would bewrong if pneumonia was much more prevalent in the underlying population.Mistakes may also result from a failure to consider that a pattern based on a smallnumber of prior observations will likely be less reliable than one based on largersamples. A second commonly used cognitive shortcut, ...