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Sunday, December 13, 2015

Predicting the future has it limits

The IOM has issued it's report on diagnostic errors which I believe highlights highlights major issues in the diagnostic realm. I have not had a chance to review it completely but I have been involved with the Society for Improved Diagnosis in Medicine (SIDM). I have heard much of discussions leading up to the report and have devoted much thought to problems in diagnosis.

One colleague in Pathology whose thinking and writings have influenced me greatly in this realm is Dr. Elliott Foucar who for more than 20 years highlighted the limitations of anatomic pathology is the diagnostic sphere. One key concept that he highlighted is that pathology made a transition in the 20th century from being a taxonomic activity to being engaged in the assessment of risk. I now have come to realize that the remainder of medicine has followed in the transition without having grasped that the transition has occurred. The SIDM and the IOM have delved into this world without explicitly recognizing the relevance of this concept to the act of making a diagnosis.

What Dr. Foucar has written about is how anatomic pathology at it origins focused on the autopsy with the sole purpose of identifying characteristics of disease which caused someone's death. An autopsy of a woman with a breast mass might identify a tumor with a specific histology and evidence of tumors elsewhere. This information was subsequently used to make predictions about live individuals who shared certain characteristics with someone already dead. For example, a live woman might present with a ulcerated 5 cm breast mass which when samples demonstrated a tumor with great similarity to what had already been observed in patients on the autopsy table. In contrast, another live woman might present with a similar mass which was showed a cyst and inflammatory cells. Histology was an amazingly powerful tool which allowed for clear separation of these distinct entities. What anatomic histology functioned as here is as a taxonomic tool, separating a being inflammatory process from a clearly malignant one. Diagnosing a ulcerated breast cancer as an infected cyst would be a clear diagnostic error, misidentifying one entity with a almost certain malignant course as a distinct entity with a benign clinical course.

Fast forward to the 21st century. Now instead of attempting to distinguish distinct clinical entities with distinct pathologies, anatomic pathology tries to separate infinite grades of dysplasias from forms of actual cancer. There is no clear line which can separate low grade dysplasias from high grade dysplasias; scoring systems are riddled with subjectivity and inconsistencies, whether the tissues are breasts, prostates, or pigmented lesions of skin, The life expectancy of those diagnosed with dysplastic lesions tend to be identical to those diagnosed with malignancies.

The transition which has occurred is one where the pathologist has moved from being a taxonomist to being an actuary. Actuaries use information to identify people or groups who are at risk for certain outcomes. Their functions are essential for certain financial entities such as insurance companies which need to put money aside to cover costs which might occur when particular events occur such as floods, fire, or illness.  They assign specific odds for such events in particular populations.

In many respects, diagnoses are always actuarial statements. Someone who presents with chest pain, shortness of breath, an abnormal EKG, and positive cardiac muscle enzymes almost certainly is having an acute myocardial infarction. This carries with it the immediate morbidity but the diagnosis has a prediction about the future built into it as well. Those affected are at near immediate risk for death. This is a prediction one does not need to wait around for months or years to assess. The acute MI diagnosis is an actuarial statement of short term outcomes.

A host of tools within the cardiovascular realm have purported to extend the ability to predict future outcomes much further into the future. We can image the coronary circulation using a variety of tools. However, moving the time frame for the predictions creates all sorts of problems, both practical and conceptually. For a patient who has clear cardiac symptoms and functional impairment short of what qualifies as an acute MI, imaging tools may allow for predictions in the non-acute time frame. However, there are efforts to push out the time windows for predictions out into years or even decades into the future. Conceptually, do "abnormal" findings observed from studies of asymptomatic individuals represent distinct diseases or diagnoses or do they represent risk factors? What represents an abnormality if the finding is common within the population studied?

Our ability to peer inside of people now is unprecedented. Whether we peer using ultrasound, x-rays, CAT scans, MRI scans, or PET scans, we can literally visualize and see what could not previously be seen unless someone was cut open on the operating table. A recent story published in the New York Times discussed new observations regarding the use of scans looking for calcification of coronary arteries. The absence of calcium seem to predictive of much lower risk of cardiac events in a 10 year time line than what conventional risk calculators might suggest. However, questions were raised because of the nearly 5% incidental findings on scan. The reality is we don't know what the range of normal findings might look like. Similarly, the ability to do ultrasound on thyroids has led to an epidemic of thyroid biopsies. We are about to embark on widespread CAT scans to detect lung cancers, most of which are likely to be indolent.

As we peer at and into into people with tools of increasing resolution and sensitivity, we will see things. Whether the things we observe will represent variations with little or not relevance to future outcomes, or whether they will represent abnormalities which place a given patient at risk for a bad outcomes will be asked. The temptation will always be there to view anything out of the ordinary as a reason to act. As the tools get more sensitive, the opportunities to observe variations will become overwhelming. When will we recommend acting and when will we write variations off as simply variations? Like screenings at the airport and those working at homeland security, we will have to deal with rare signals within a sea of noise. Ideally, we can become like actuaries, if we can accumulate enough solid data to allow us to make data driven decisions. Until then, we will make our decisions driven by fear and complacency.

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