Thursday, August 22, 2013

Conservative Medicine: What's new about this book?

How do you know when you are sick? This may seem like a silly question at first blush, but the proliferation of increasingly sensitive screening tests that aim to diagnose diseases long before they can cause symptoms (and, hopefully, deliver treatments that will be more effective during the asymptomatic stage) has changed the answer. Today, more patients than ever find out that they're sick not because they feel sick, but because a doctor tells them they are.

Your blood pressure or sugar level or cholesterol level is too high. You have a prostate cancer that you can't see or feel - that the doctor can't even feel - but that a pathologist diagnosed by looking at a small sample of cells from a blind biopsy needle that followed a "simple" blood test your doctor might not have bothered to tell you about. Some of these abnormalities will eventually cause suffering or premature death. Many of them won't. It's not possible to know for sure which is which. So naturally, you have aggressive treatment, just in case, and experience all of the resulting side effects.

Although long ignored or downplayed by screening advocates, overdiagnosis and overtreatment have been recognized as important problems in medicine for years. In a few weeks, I will attend an international conference on Preventing Overdiagnosis at the Dartmouth Institute for Health Policy and Clinical Practice. The conference website includes an excellent reading list of books about the topic written by prestigious experts. So where does Conservative Medicine fit in? What will my book say that hasn't been said already?

In my view, overdiagnosis would be much less of a medical problem if our definitions of disease weren't so elastic. A study published last week in PLoS Medicine determined that most expert guidelines published since 2000 expanded the definitions of diseases and eligibility for treatment - for example, lowering the threshold for "high" cholesterol or using a more sensitive diagnostic test for a heart attack. This might not necessarily be a bad thing if it meant that more patients would benefit from effective treatments, but the study researchers also found that 3 in 4 guideline panel members had received payments from pharmaceutical or device companies that stood to benefit directly from more expansive disease definitions. More people with "high" cholesterol meant more prescriptions for cholesterol-lowering drugs, and the scientists who lowered the threshold were on the payroll of the companies that sold those drugs. Hmm.

A related phenomenon is epidemics of "predisease" - people who do not have disease but are considered more likely than others to develop that disease in the future. Prehypertension, prediabetes, and osteopenia are common examples of such conditions. As family physician and public health specialist Anthony Viera explained in this Epidemiologic Reviews article, the concept of predisease only makes sense if people with predisease are at much greater risk than others of developing true disease, if an intervention exists to lower that risk, and if the benefits of that intervention outweigh the harms in the population. That last point is worth repeating: if the benefits of that intervention outweigh the harms. Just being told you have predisease will change your life, and not always for the better.

In addition to taking a hard look at the effectiveness of screening tests, Conservative Medicine will argue that expanding disease definitions and being careless about labeling patients as prediseased often lead to more harm than good.


This is the third in a series of brainstorming posts about a book that I plan to write titled Conservative Medicine.