Sometimes one wants to focus on a disease low in the differential diagnosis.
Example to work through
Consider the case of a 43-year-old man who had onset over ~1 year of tremor and ascites (fluid buildup in spaces in the abdomen), and anemia of unknown duration. A variety of liver diseases are worth considering, but one with low probability given this clinical situation is Wilson disease, as illustrated in the image below (Registered users can click the images below to jump into the software; some videos may be helpful in navigating from there):
The useful findings focus on common causes of liver disease, but since Wilson disease is so treatable (and can be fatal if left untreated) one might want to focus on ruling in or ruling out the disease, even though it is considered to have low probability. Seasoned clinicians know that sometimes diseases don’t present in the “normal way” and consider more than the top few diagnoses.
Clicking Wilson disease selects it as the active disease and offers a “Rule in or out active disease” option. Selecting it, a different set of Useful findings are offered on the “Add findings” tab. Among these are checking the iris for Kayser-Fleischer rings and collection of family history.
Selecting “Add tests” focuses on assessment of copper metabolism, used to diagnose Wilson disease.
The cognitive error associated failure to use “rule-in, rule-out” thinking is called “Representativeness”: dismissing a disease that doesn’t match the classic clinical pattern. It is easier to avoid this problem if the findings relevant for ruling in or out the disease can be summoned up readily.
This page is part of a series on the Elements of Diagnosis.
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