Wednesday, September 26, 2018

Treating the differential diagnosis

Generating and then re-assessing the differential diagnosis for a patient is critical. It is important even when we feel fairly certain about the working diagnosis already assigned. At any point in the future, we may learn from a new observation that not all swans are white.

At times, the definitive diagnosis is not clear. Often, to make the definitive diagnosis, data from the future are needed in the present. This is not possible. At the present moment, we do not have the full trajectory of the patient's illness course available to us for review. We have (some of) the past (the parts that we know from the history); we have the present (the signs and symptoms readily available); and, we have knowledge about the typical trajectories of illnesses that are on our differential. Clearly, we face limitations in diagnosing patients.

Generating and re-assessing the differential diagnosis helps us hedge against this uncertainty. It includes possible diagnoses for this particular patient at this particular time under these particular circumstances. Thinking through the differential diagnosis involves considering the key features of each diagnosis, including probability and impact, to characterize this patient's current state of affairs. We might think, "It could be X given A, B, and C; but, it could, though less likely, be Y given D and E, and if it were Y, then it would have Z implications for care." Thus, in practice, we may find value in thinking about how to treat the differential diagnosis.

For example, a 20-year-old male presents with a complex picture: for the past year, he has had periods of low mood, high mood, and psychosis that impair his function. The details about these affective and psychotic experiences are important; but, in the limit (or at the margin), the following reality remains: knowing the future would provide a lot more diagnostic clarity in the present. A leading diagnosis, based on the nature of the details (the phenomenology), could be major depressive disorder with mixed features. But it could be bipolar disorder (I or II) with psychotic features; or, it could be first-episode schizophrenia. Given the different courses that characterize these illnesses--the prognosis--there is a reality that "time will tell" or that "the true diagnosis will declare itself."

However, we are challenged with treating the patient in the present. Over time, as we care for this patient, we will continually re-assess the differential diagnosis in light of new data (this data stream is the "trajectory"), and our management of the patient will evolve accordingly. But at each moment, as we grapple with the uncertainty of our working (or leading) diagnosis, we could make treatment decisions, when possible, that account for both the leading diagnosis and the other possible diagnoses on our differential.

This is a "thinking-about-thinking in medicine" dynamic that I'm exposing to the envelope of serendipity (via blogging) to learn more about and to integrate into my own practice as a physician.

It seems that practicing epoche might inform how to treat the differential diagnosis.

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