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A Chicken vs. Egg Issue in Medicine

by Scott MacStravic

A report yesterday indicated that there is a strange chicken or egg question about how at least one medical diagnosis is made.  The issue is: Does the diagnosis precede the choice of treatment, or does the choice of treatment come first, then cause the diagnosis in order to justify the treatment?

It has long been known that physicians are idiosyncratic in their approach to diagnosing patients.  In some cases, they prescribe a treatment in the hopes that it will show what the diagnosis was by either working or not working.  The character “House” in that eponymous TV show is fond of this approach.  And it makes sense when the risks and side effects of the treatment are minimal, and no other approach to diagnosis has worked.

Physicians’ diagnoses and treatment choices are also understandably influenced by their specialty training and experience.  Just as the “law of the hammer” notes that when you have a hammer in hand, more things begin to look like nails, so when you specialize in one kind of treatment, such as surgery vs. chemotherapy vs. radiation therapy for cancer, the choice of treatment is bound to be influenced by which the physician specializes in.

But “scientific evidence” for the dynamic “loop” of mutual causation emerged in a review of the rate of diagnosis of depression before vs. after “black box” warnings were issued by the Federal Drug Administration about the use of the class of anti-depressants called SSRIs.  In the five years before the warning that these drugs can cause teen suicide, the depression diagnosis rate had climbed from 6 to 11 per thousand, among managed care plan members.  Then when the FDA warning was issued in 2005, the rate decreased significantly, from 8.0 to 5.8 for men, and from 17.4 to 12.4 for women.

The use of SSRIs understandably dropped, as well, from 53% of depression episodes to only 22% and even non-SSRI anti-depressants were used less often.  On the other hand, the number of patients who received at least some psychotherapy and alternatives to anti-depressants did not decline, as should be the case given that the warning only applied to anti-depressants. [“Depression Diagnoses Down After Drug Warning” MSNBC.comSep 5, 2007]

But what was the cause of the decline in the diagnosis of depression?  There appears to be no logical connection between the decline in the use of anti-depressants as a cause of the decline in diagnosis.  That is unless physicians were heretofore pressured by patients to prescribe anti-depressants for their depressed feelings, and when the warning was issued, the “popularity” of the diagnosis went down.  Or perhaps, physicians were previously prescribing anti-depressants as a diagnostic test, and non longer used this test once the warning was issued.

As patients, we non-physicians may expect, and even prefer that diagnoses come first, and are based on something other than the need to justify a presumption or guess about the diagnosis.  The fact that diagnoses of depression decreased so markedly, so fast, after increasing so dramatically before the FDA warning, at least suggests that diagnoses were being made on less than model criteria and using a variety of processes that may not fit “evidence-based medicine”.

There are technologies that can assist physicians in making diagnoses, involving computer programs that work physicians through a differential diagnosis program from symptoms to possible to most likely diagnosis.  And physicians have been shown by autopsy studies to misdiagnose patients (at least the ones who die) between 8% and 24% of the time.  Given this finding, one would think physicians might welcome technological assistance, but they are often described, and many times dismissed as “cookbook medicine”. [E. Donaghue “For Doctors, Diagnosing Gets a Technological Boost” USAToday.com Sep 5, 2007]

Even though cookbook medicine, where presumably computers take over completely in diagnosing and choosing treatments, is a threat to the “art” of medicine, most physicians are perfectly capable of using the technology as a guide to, rather than a substitute for their own judgment.  And given the chicken vs. egg issue illustrated by the depression example, consumers might prefer that technology were used more often.

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