Knowledge and the Half-Life of Truth

Once upon a time I could dream in German and read Caesar's Gallic Wars in Latin. I knew Avogadro's number, Bernoulli's principle, and the Laws of Thermodynamics. I could compose in iambic pentameter, recite a few lines from Horatius at the Bridge, and write the ancient Greek alphabet. Polynomials, logarithms, and quadratic equations got me into medical school. I was once very good at all these things. I even understood fractals and chaos theory. Now, on a good day, I can calculate the volume of a cube or the area of a circle, remember pi to the second decimal place, and recite the 11 times table. As I recall, the speed of light is 186,000 miles per second. Don't ask me what it is in metric. If I look at my watch I can remember the date. And, generally, the world is a pretty chaotic place.

I have already forgotten several times the amount that I still know. I don't mind losing the facts and the information; it's the lost knowledge that I regret. Where did all that knowledge go? I thought it was just disuse atrophy. Turns out, according to an article in Nature (2002; 418:970-75), something called PP1 (protein phosphatase 1) is going around my soft drive deleting unused files. Intellectually, I can cope with that. "Use it or lose it." I can even cope with the idea that my soft drive ain't what it used to be.

But what about all that stuff I crammed away in medical school? "Infectious" and "serum" are now "A" and "B." "Australia" is "surface" and "non A, non B" turns out to be "C." Diabetics check blood glucose not urine ketones. Alcohol is still bad for my liver but is good for my heart. (I can cope with that.) Many of the facts we learned in medical school were useless from the beginning.

Then I became a resident. A fact junkie and information addict, trying to know everything about everything. And finally a consultant, coping by learning more and more about less and less. And I became a fact and information producer but now am embarrassed to say that a PubMed author search of "sullivan sn" turned up a paper I don't even remember writing.

Once upon a time a single man could grasp the sum of medical knowledge. Osler recorded it in the 1,079 pages of The Principles and Practice of Medicine. My 1996 CD-ROM of Scientific American Medicine contains 385 megabytes. The National Library of Medicine's MEDLINE has more than 12 million citations from more than 4,500 journals. I follow all of this on the internet and faithfully read, cover to cover, the paper copies of five general medical journals, five journals in my subspecialty, and the hundredweight of throwaway stuff that crosses my desk each year.

I have seen more than my lifetime quota of Wilson's disease and Zollinger-Ellison syndrome, but, still, each article draws my attention. Much of what I read I already know. A small percent is new. Little is useful. Some, like the Nature article on PP1 and a recent BMJ filler on the genetics of earwax is interesting and might be useful in cocktail-party conversation. But a big chunk isn't (and never will be) of any use in my medical practice.

So why do I read about things I may never see and almost certainly will never treat? Information addiction? Because I read everything and anything that passes over my desk or through my mail slot. Fear? Because I'm afraid of not knowing the answer to a question no matter how obscure the problem. Will I be thought less of for having missed a diagnosis? I don't know, so I continue to read my journals.

But the trouble is, every now and again somebody changes the truth. Fifty years ago, my mother's radical mastectomy and radiotherapy were the best treatment available. Now, a lumpectomy would be just as good and she wouldn't have lymphedema. Twenty years ago duodenal ulcers were all about diet and stress and too much acid. God, how embarrassing to think that I used to tell medical students that Pepto-Bismol had no role in their treatment. And my wife, on my advice, took HRT for more than a decade to protect her heart – and other things. She has now gone cold (or is it hot?) turkey.

Sometimes, I think it would be nice to pull a Rip Van Winkle. Go to sleep and wake up when the fighting is over and the real true truth has been found.

And, now, barring an infusion of telomerase or the return of Ponce de Leon, I've passed the half-life of my life and I find that the half-life of truth in medicine is only 45 years (Lancet 1997; 350:1752 and Lancet 1998; 351:376). Even in my limited sub-subspecialty of hepatology, 19% of what I learned is obsolete and 21% was never true in the first place. And the methodological quality of a study did not affect its likelihood of being or remaining true. Even more distressing is that the studies with negative conclusions were five times more likely to be true 50 years later than the studies with positive conclusions (Ann Int Med 2002; 136:888-95). And to make it worse, I am now into that very difficult phase of my life when I am actively trying to unlearn the things that I once believed were gospel. I still remember my very first telephone number but not the one I had only six months ago.

I've learned that in medicine nothing is "never" and it's certainly never "always." And the Heisenberg Uncertainty Principle only applies if you are raising teenagers. I just wish somebody would publish the Journal of Probably True and Immediately Useful Information and that all of its articles would have informative titles. Something like, "Penicillin Cures Syphilis" rather than, "The Role of Dietary Microparticles and Calcium in Apoptosis and Interleukin-1 Release of Intestinal Macrophages."

And this is the truth, as I believe it to be, in the the Year of our Lord, 2008.

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