Illustration by Gianpaolo Pagni
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Why Doctors Make Mistakes
By Jerome Groopman, M.D., September & October 2008
Too often, physicians make snap decisions. Here are three questions to help get you to the right diagnosis
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Not long ago I spoke with a middle-aged woman whose mother had been misdiagnosed with Alzheimer’s disease. The elderly woman’s memory was fading, and her family was close to admitting her to a nursing home. Luckily, the family decided to get a second opinion from a neurologist at a different hospital. It turned out the woman did not have Alzheimer’s at all but, rather, vitamin B12 deficiency, a well-recognized cause of dementia. Her mild anemia, also due to vitamin B12 deficiency, had been written off by her internist as being due to “old age.” Injections with the vitamin fully reversed the anemia and restored her thinking.
Unfortunately, medical misdiagnosis is not a rare phenomenon. About 15 percent of all patients are misdiagnosed, and half of those face serious harm, even death, because of the error. Contrary to the general impression that most misdiagnoses result from a technical foul-up, such as mislabeling someone’s X-ray or mixing up a blood specimen in the laboratory, most cases are due to mistakes in the mind of the doctor.
Most errors are due to mistakes in the doctor’s thinking.
How do doctors think through a case? Making an accurate diagnosis involves arranging the information from the patient’s symptoms—findings from physical examination and laboratory tests—into a pattern. A doctor then superimposes this pattern onto a template of the typical case that exists in his or her mind. But this effort at pattern recognition doesn’t always work. Why not?
First, there may be incomplete or misleading information. Patients may not feel comfortable reporting all their symptoms to a doctor—or, as studies show, physicians may prematurely cut off a patient who is reciting his or her problems (in fact, research reveals that most physicians interrupt a patient within 18 seconds of beginning an interview). Second, pattern recognition is difficult because cases may not be “typical.” This means that diseases can have different manifestations, sometimes quite subtle, because every individual is different. Most significant is how the doctor selects the clinical elements, weighs their importance, and arranges them in his or her mind, a process that can result in several different patterns, leading to quite different diagnoses.
There are three major cognitive mistakes that can occur in the mind of the doctor and lead to misdiagnosis. The first is termed anchoring, meaning the tendency to grab on to the first symptom, physical finding, or laboratory abnormality. Such snap judgments may be correct, but they can also lead physicians astray. A second common cognitive error is termed availability. This refers to the tendency to assume that an easily remembered prior experience—what is most readily available in the physician’s memory—can explain the new situation he or she is trying to diagnose. The third mistake in thinking is termed attribution, and this accounts for many of the misdiagnoses in the elderly. Attribution refers to the tendency to mentally invoke a stereotype and “attribute” symptoms to it. Alas, often this stereotype is a negative one, such as an older person who is seen as a complainer, a hypochondriac, or a person unable to cope with his or her naturally declining abilities. The doctor ignores the possibility of an illness not specifically linked to “old age,” as in the case of the woman with B12 deficiency. Imagine how much it would have cost in physical resources—not to mention emotional ones—to keep her in a nursing home for the rest of her life.
What can patients do to help prevent medical thinking from going astray? I have formulated three simple questions to ask. It is quite appropriate for patients and their families to pose these questions to their doctor when he or she is making a diagnosis.
1. “What else could it be?” This question helps to prevent an anchoring error or an availability error, where a diagnosis is formulated too quickly in the physician’s mind because it corresponds to the initial symptom or abnormality (anchoring) or because it is most familiar to the doctor (availability).
2. “Could two things be going on to explain my symptoms?” In medical school doctors are taught to be parsimonious in their thinking, meaning they are taught to identify a single cause to explain a variety of complaints and symptoms. But sometimes a patient can have two medical problems simultaneously. Physicians sometimes stop searching once they find an initial problem, even if the patient does not fully recover.
3. “Is there anything in my history, physical examination, laboratory findings, or other tests that seems not to fit with your working diagnosis?” All physicians tend to discount information that seems to contradict their hypothesis. This bias can lead a doctor down the wrong path; his or her anchor diagnosis may be so firmly fixed that this leads to ignoring contradictory data.
I have found that smart and dedicated physicians are able to explain their thinking, and they are able to put into clear and accessible lay language how they arrived at their working diagnosis. In some instances these questions may cause the doctor to go back and reexamine assumptions, to think again, and to come up with a different, and now correct, diagnosis. All doctors want the best treatment for their patients, and the best treatment involves the most open-minded thinking.
Jerome Groopman, M.D., is the author of the New York Times bestseller How Doctors Think (Mariner Books, 2008).
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