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Step 1: Identify the Problem
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Be certain you understand what the patient is telling you (Figure 1-1). Sometimes “I’m tired” means “I become short of breath when I walk” and at other times means “My muscles are weak.” Construct a complete problem list consisting of the chief complaint, other acute symptoms and physical exam abnormalities, laboratory test abnormalities, chronic active problems (such as diabetes or hypertension), and important past problems (such as history of bowel obstruction or cancer). Problems that are likely to be related, such as shortness of breath and chest pain, should be grouped together. It is necessary to accurately identify the problem every time you evaluate a patient.
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Step 2: Frame the Differential Diagnosis
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The differential diagnosis should be framed in a way that facilitates recall. It might be possible to memorize long lists of causes, or differential diagnoses, for various problems. However, doing so would not necessarily lead to a useful organization of differentials that helps you remember or use them. Instead, it is preferable to use some kind of problem-specific framework to organize differentials into subcategories that are easier to remember and often clinically useful. Problem-specific frameworks can be anatomic, a framework often used for chest pain; organ/system, used for symptoms with very broad differentials like fatigue; physiologic; or based on pivotal points (defined below). Each chapter in Symptom to Diagnosis begins with a problem-specific framework for the differential. Using such frameworks has been shown to improve the diagnostic accuracy of medical students.
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Step 3: Organize the Differential Diagnosis
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Structuring the differential diagnosis into clinically useful subgroups can enable you to systematically work through the differential diagnosis. Sometimes the framework that is easiest to remember, such as grouping causes of dyspnea as cardiac or pulmonary, does not facilitate reasoning. Then, reorganizing the differential in a way that helps you understand the order in which to consider various diagnoses is necessary. The most clinically useful differentials are organized using pivotal points, one of a pair of opposing descriptors that compare and contrast clinical characteristics. Examples include old versus new headache, unilateral versus bilateral edema, and right lower quadrant pain versus epigastric pain. When pivotal points are used to frame the differential in the first place, it is not necessary to reorganize the differential to create a diagnostic algorithm.
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You can frame and reorganize the differential yourself or find a source that does so in a way that makes sense to you. Each chapter in Symptom to Diagnosis contains a diagnostic algorithm that uses pivotal points to highlight logical reasoning pathways for each symptom. Steps 2 and 3 need to be done only once for each clinical problem you encounter; with experience, you will develop a repertoire of logically framed differentials and structured diagnostic approaches to problems you encounter.
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Step 4: Limit the Differential ...