Body Scanning and Philosophy
The Midjourney promise of body ultrasound, like the total body MRI body imagers, suffer the same problem--and it isn't technical, it's philosophical
Journalist Christina Farr hosted this interview/podcast with three doctors regarding the idea of preventive total body imaging to extend life. It’s a good discussion. My friend Venk Murthy particularly excels.
The concept is enticing: many diseases (heart and cancer, primarily) lie dormant before causing death. A scan could find these early, at a stage where surgery or medicine could cure. Doing this would extend life.
Even some doctors are fooled, saying they went into medicine to prevent disease not just throw pills at diseases that could be cured if caught earlier.
Of course, anyone who is tempted to fall for this folly fails basic numerical literacy.
That is, if a disease has a 1% prevalence (and many of the diseases found on these scans have an even lower incidence) and a test is 90% sensitive and 90% specific most of the “positives” are false positives.
To review the calculation. It’s disease prevalence multiplied by the likelihood ratio (sensitivity/1-specificity) equals the after test probability.
1% x [.9/.1] = 9%. Meaning that if 100 people have a positive scan, 9 will be a true positive and 91 will be false positive.
We learn this basic stuff in medical school then it is promptly forgotten. It’s why mammography has such a hard time reducing breast cancer outcomes. The inherent problem is looking for low incidence conditions. Even a good test (90% sensitive and specific) produces more false positives than true positives when disease prevalence is low.
Every doctor can tell you horror stories of false positives. The person who has a coronary calcium scan and is found to have a lung nodule—who nearly dies during the biopsy procedure of the non-cancerous nodule, for instance.
But this self-evident medical fact is not the biggest problem with these total body scans. Let me show you two more.
First, in the opening paragraph of the Death of Humane Medicine, the late Dr. Petr Skrabanek laid out the biggest problem with this idea:
Health, like love, beauty or happiness, is a metaphysical concept, which eludes all attempts at objectivisation. Healthy people do not think of health, unless they are hypochondriacs, which, strictly speaking, is not a sign of health. Similarly, when our organs perform their functions perfectly, we are not aware of them. It is the absence of health that gives rise to dreaming about health, just as the real meaning of freedom is only experienced in prison.
The pursuit of health is a symptom of unhealth.
Healthy people do not think of health. The pursuit of heath is a symptom of unhealth. As I age, fewer ideas ring truer.
For the second problem, I cite the great book Conflict of Visions by Thomas Sowell.
The unconstrained vision holds that there are ideal solutions to every problem and that compromise is never acceptable. Just tweak human nature enough and you can fix all that ails society.
The constrained vision holds that human nature has never changed, cannot be modified and, here, compromise is essential because there are no ideal solutions, only trade offs. Constrained thinkers favor evidence to sort out these tradeoffs.
Now apply that frame to medicine.
Unconstrained thinkers dominate medicine. More is better. We can solve human disease. We just need to do more tests, give more drugs, keep innovating. Everything is modifiable. Of course, there is profit in being an unconstrained thinker.
The concept of total body scanning is unconstrained thinking raised to exponential levels.
I am a constrained vision person. I am shocked more doctors are not this way. It’s as if we ignore what we see everyday. We see patients survive an MI only to die a year later with pancreatic cancer; we see thousands of diseases affect our patients.
The idea that a scan or search from one disease could save you belies any sense of health and disease.
Religious people say people die when God calls them. I am not that religious but I am absolutely convinced that we die when it is our time. And it is only modifiable on the margins.
You wear a seatbelt (low harm) and do not ignore a bump in your armpit or new symptoms. You do basic things, mostly pay attention. I’ve seen cyclists call their new breathlessness asthma when it was an LAD lesion that could have been fixed before causing cardiac arrest. These are the “evidence” parts in the constrained vision.
Short of paying attention, the wealth of diseases that could kill you are hardly worth chasing. Better to healthily not pursue health.
Finally, the corollary of this philosophy pertains to doctoring: yes, doctors are supposed to treat the sick. Our job is to help people who are asking for our help. Prevention is best left to a person’s smart choices and good luck.
John, thank you so much for this super post. Coincidentally I just covered the same topic with the same math, but from the standpoint of blood tests for early cancer detection, the so-called “liquid biopsies.“. You added the philosophy and I really appreciated it. https://jamesstein18.substack.com/p/multi-cancer-early-detection-tests?r=p5sxn&utm_medium=ios
I share your concern about why more physicians do not follow the constrained vision. However, I have read much of Thomas Sowell in the past but never Conflict of visions. But the concept of the unconstrained versus constrained vision seems to be in the pattern of a several 1000-year old conflict between Plato and Aristotle. The idea of the deductive versus inductive reasoning. I have just finished reading Arthur Herman's The Cave and the Light and I am going to read it again. It covers 2500 years of the philosophy of the conflict of this vision and its impact on society, politics as well as science. I took this moment to upgrade my subscription to paid. After 30 years in medicine I am starting to understand what I see things so differently than many other physicians.