Often a patient seems to have a familiar disease. In such situations, however, it is often worthwhile to consider other diseases that can appear similarly. One of the 3 cognitive modes of starting the process of diagnosis is to develop a differential diagnosis by considering the findings typical of the suspected disease.
Example to work through
A 65-year-old man appeared to have Parkinson disease. After entering the age and sex on the Start screen, 3 cognitive modes are offered, including “suspected disease”:
Clicking on the blue magnifying glass button at the bottom of the image (or on the blue magnifying glass on the top black Navigation bar) and searching for Parkinson disease directs you to the Profile Disease screen, where you can specify recent onset of tremor and bradykinesia using the components to the left of the findings (click the images below to jump into the software):
Notice that this screen shows you the frequency of each finding in the disease as the total length of the bar, with details about the age of onset in black, brown, and purple. The length of the frequency bars is less than 100%, reflecting the fact that not all patients have all findings described in the disease. Such variable presentation is one of the factors that makes diagnosis difficult.
Clicking the Dx button on the top black Navigation bar shows a differential diagnosis with Parkinson disease ranked #1, but Dementia with Lewy bodies is #2; in the image below the Add Tests tab is selected.
One can then comment on various findings useful in distinguishing among the diseases in the differential diagnosis, such REM Sleep Behavior disorder, in which an individual acts out dreams.
Adding that finding as recent elevates Dementia with Lewy Bodies to #1 in the differential diagnosis.
One can view the frequency of a finding in the differential diagnosis by using the green V on the top black navigation bar. This shows the influence of a finding on the differential diagnosis; in this example, REM sleep behavior disorder is more common in dementia with Lewy bodies than in Parkinson disease.
In this case the diagnosis of Dementia with Lewy Bodies was not appreciated, even though the wife had described a history highly suggestive of REM Sleep Behavior. Unfortunately, the patient was treated with neuroleptics and deteriorated rapidly (to see why, click in the software on the red Risk asterisk to the left of Dementia with Lewy bodies).
The cognitive error associated with not using this element is called “Premature closure”: jumping to a diagnosis and failing to consider alternative diseases.
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