Art, Science, and Observation

This is one of the most important chapters of the book, because it considers the methods and concepts of evaluating the signs and symptoms involved in diagnostic reasoning. The previous chapters discuss the “science” of medicine by explaining the techniques for interviewing and performing the physical examination. The ability to make the “best” decision in the presence of uncertainty is the “art” of medicine. But there are rules and standards for the practice of this art, and these are the focus of this chapter.

The primary steps in this process involve the following:

Data collection is the product of the history and the physical examination. These can be augmented with laboratory and other test results such as blood chemistry profiles, complete blood cell counts, bacterial cultures, electrocardiograms, and chest radiographs. The history, which is the most important element of the database, accounts for more than 70% of the problem list. The physical examination findings contribute an additional 20% to 25% of the database; less than 10% of the database is related to laboratory and other test results.

For example, suppose the interviewer obtains a history of dyspnea, cough, earache, and hemoptysis. Dyspnea, cough, and hemoptysis can be grouped together as symptoms suggestive of cardiopulmonary disease. Earache does not fit with the other three symptoms and may be indicative of another problem. For another patient who complains of epigastric burning relieved by eating and whose stool is found to contain blood, this symptom and this sign should be studied together. These data suggest an abnormality of the gastrointestinal tract, possibly a duodenal ulcer. Although patients usually have multiple symptoms or signs from a pathologic condition, they may not always manifest all the symptoms or signs of the disease being considered. For instance, the presence of polyuria and polydipsia in a patient with a family history of diabetes is adequate to raise the suspicion that a lateral rectus palsy may be related to diabetes, even if diabetes has not previously been diagnosed in this patient. In another patient, a 30-pound weight loss, anorexia, jaundice, and a left supraclavicular lymph node are suggestive of gastric carcinoma with liver metastasis to the porta hepatis. This illustrates the concept of data processing multiple symptoms into a single diagnosis. The process has sometimes been likened to the rule of Occam’s razor: The simplest theory is preferable—in this case, that all the symptoms can be explained by one diagnosis. Although it is a useful rule to keep in mind, it is not always applicable.

The presence of a symptom or sign related to a specific problem is a pertinent positive finding. For example, a history of gout and increased uric acid level are pertinent positive findings in a man suffering from excruciating back pain radiating to his testicle. This patient may be suffering from renal colic secondary to a uric acid kidney stone. The absence of a symptom or sign that, if present, would be suggestive of a diagnosis is a pertinent negative finding. A pertinent negative finding may be just as important as a pertinent positive finding; the fact that a key finding is not present may help rule out a certain diagnosis. For example, the absence of tachycardia in a woman with weight loss and a tremor makes the existence of hyperthyroidism less likely; the presence of tachycardia would strengthen the likelihood of hyperthyroidism.

An important consideration in any database is the patient’s demographic information: sex, age, ethnicity, and area of residence. A man with a bleeding disorder dating from birth is likely to have hemophilia. A 65-year-old person with exertional chest pain is probably suffering, statistically, from coronary artery disease. A 26-year-old African-American patient with multiple episodes of severe bone pain may be suffering from sickle cell anemia. A person living in the San Joaquin Valley who has pulmonary symptoms may have coccidioidomycosis. This information is often suggestive of a unifying diagnosis, but the absence of a “usual” finding should never totally exclude a diagnosis.

Finally, “A rare disease is not rare for the patient who has the disease.” If a patient’s symptoms and signs are suggestive of an uncommon condition, that patient may be the 1 in 10,000 with the disease. Nevertheless, statistics based on population groups provide a useful guide in approaching clinical decision-making for individual patients.

Diagnostic Reasoning from Signs and Symptoms

Unfortunately, decisions in medicine can rarely be made with 100% certainty. Probability weights the decision. Only if the cluster of symptoms, signs, and test results is unequivocal can the clinician be certain of a diagnosis. This does not occur often. How, then, can the clinician make the “best” decision—best in light of current knowledge and research?

Laboratory tests immediately come to mind. But signs and symptoms obtained from the patient’s history and physical examination perform the same function as laboratory tests, and the information and results obtained from signs, symptoms, and tests are evaluated in the same way and are subject to the same rules and standards of evidence for diagnostic reasoning. Also, signs and symptoms actually account for more (90%) of the developing problem list than do laboratory test results (<10%).