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"Yes, ideally we would run every possible test on any patient that walks in with a stomachache. But there are limits to our economy and to doctors' time. It's a complex problem."

The problem isn't necessarily economical, a lot of those tests are actually very cheap.

The problem is that most tests have high false-positive rates, which you account for by using bayesian inference: the probability of having the disease when you have both symptoms and a positive result on the test, is very high, even if the test itself has a high false-positive rate.

But if you just run all tests in a healthy patient, you'll get back a lot of false positives.

https://people.ucsc.edu/~abrsvn/intro_bayes_1.pdf

This actually depends on how rare the disease is. With a relatively high false positive rate and the disease being quite rare (given symptoms that arguably match), the false positives dominate the true positives anyways.

It does get worse if you run everything on a healthy patient though.. you definitely get back many false positives.

I see. I was wrong to make assumptions about what the limitations are.

Thanks for the link. I wonder how closely doctors follow bayesian inference (and how many know about it). It seems pretty intuitive, so maybe it's already largely applied?

"It seems pretty intuitive, so maybe it's already largely applied?"

It is! That's why doctors don't order every single possible test every time you show up sick!

That's also why consumers SHOULD NOT be testing by themselves without medical supervision (I'm looking at you, Elisabeth Holmes and Theranos).

It is at least implicit in testing practices; the reason diagnosis often involves a series of tests is that they first screen with cheap, low-false-negative testing, then apply more expensive tests to weed out the false positives. But of course the rarer the disease, the harder that second phase becomes.

In one of my courses in medical school, our professor, a physician, told us that many doctors follow Bayesian inference without even realizing, based on their experience and education. The best doctors recognize this ang educate themselves on epidemiological studies to better use tests and procedures and medications to take care of patients most effectively.

I've actually been going through this recently with a series of cancer tests with a high false positive rate. When I was discussing it with my specialist he said that he and other doctors don't necessarily think of it in rigorously Bayesian terms, but they're familiar with the sensitivity and specificity of each test and have a pretty strong understanding of what that means based on priors.

Talking to medical students I get the same impression. The refrain I commonly hear is that high sensitivity tests can rule something out, and a high specificity test can rule it in. Obviously that's a reasonably shallow understanding, but when they combine that with their intuition of a prior it seems like they get pretty good results.

I don't think it's that they get good results, but moreso that it's the conventional wisdom (or "standard of care") and a good mechanism for learning from and properly attributing bad patient outcomes just isn't there. I doubt anybody has told them that their patient died or was given inappropriate treatments because they didn't have the proper appreciation for Bayes theorem, even if it were the root cause. That's just not the culture of medicine today.

The ailments you describe though can certainly be debilitating but require no underlying diagnosis. Me and my mother have horrible migraines, no one knows why but it doesn't matter because I was prescribed a medicine, didn't work. I was prescribed a second one and it worked and it is frustrating and it sucks but quality of life is the same.

For all those ailments, we can treat stomach aches, dizziness, headaches. But when one day you're relatively healthy and 3 months later you can't walk then you NEED a diagnosis. Its like when you get stomach aches vs stomach aches plus throwing up for 99% of the food you eat or bleeding stools and frequent constipation then you get a diagnosis to figure out what is going on, usually a colonoscopy/MRI for IBS or UC.

For most things we don't need a proper diagnosis. A ligament tear grade 1,2,3 can be treated without any radiographs. Often similar conditions can be treated with the same exact splint or therapy. There is no need to further diagnose if quality of life can be the same with less than 6 months of treatment and medications.

But when you can't work or do normal daily life functions al of a sudden, you can't just give up and say too bad. Unfortunately if I had Medicaid that is exactly what would have happened. Doctor classifies it under a broad diagnosis requiring little tests and you're screwed for life. Since I had ppo from work, I went to a bunch of doctors until I got a clear obvious diagnosis. Now that I have a diagnosis I can improve.

Also, if problems aren't certain as they are chronic, widespread or hard to diagnose you see certain specialists who are trained to diagnose. You don't see a general physician

To be clear, I'm not at all saying that false negatives are acceptable. I'm sorry that your migraines went undiagnosed for so long and am happy to hear that you were eventually helped.

I just wanted to point out that it is a complex issue because there most likely are a significant number of patients who have pyschosomatic pain. And because of them it's, unfortunately, difficult to achieve comprehensive testing. (But I don't want to sound like I'm blaming this group very much. Stress can be terrible, especially when it's chronic. Though freeloaders are a different problem..)

> Also, if problems aren't certain as they are chronic, widespread or hard to diagnose you see certain specialists who are trained to diagnose. You don't see a general physician

This is actually (imo) one of the largest failings in the UK's various health systems -- Diagnosticians as you have them in the US, do not exist. The entire system relies on GPs keeping up to date on various diseases and symptoms. This means that a lot of the time diseases that typically present with vague symptoms, like cancer, can go undiagnosed for years.

We have diagnosticians? This is my first time hearing of them so they must be pretty rare.

Would have been nice when one of my family members was in the hospital for 6 months. Maybe he was talking about Dr. House?

> Doctor classifies it under a broad diagnosis requiring little tests and you're screwed for life.

I don't understand. Can you clarify what you're saying?

A stomachache is hardly the same as years of debilitating pain and fatigue. One might think a chronic condition that presents consistently enough in type of symptoms across more than a million patients may be worth considering as possibly physiological in nature. Certainly this team at Stanford believed so.

The symptoms of this syndrome include pain, dizziness, and headache so that's three of the four you mentioned. The very story is about how this syndrome is often not diagnosed properly. That means that some portion of MUPS may be explained with the tests the team at Stanford is developing.

Just dismissing it because there's not yet a great test is the problem they're trying to solve.

The commenter to which I replied seemed to be extrapolating the idea past Chronic Fatigue Syndrome to all cases where patients are not successfully diagnosed for reported pain. Thus my argument was not specific to CFS.

I agree that it seems unlikely for years of fatigue to be psychosomatic, but we won't know the numbers until there is a test.

When you have chest pain you better get to a doctor, it might be a heart attack. Most chest pain is not a heart attack, but only a doctor can tell. Thus I expect most people to run to the doctor over "nothing": it probably is nothing but you need to verify that.

also, psychological illness can be just as devastating and debilitating as physical illness.

OCD for example leads to years of life lost to disability.

I don't think the CFS crowd realise how fucking annoying they are when they dismiss psychological illness as "all in your head".

That is a pretty sweeping generalization to make. I've been sick with ME/CFS for several years now and I've never come across another patient dismissing psychological illness as not debilitating. Instead, many that I know have premorbid or comorbid psychological illness and know firsthand how debilitating psychological illness is.

If a person with OCD was told that their illness was due to poor lifestyle choices and that they could be cured of their OCD if they just stop believing they have OCD and that they just need to get to sleep on time and get a bit of exercise, they would probably not appreciate that. This is how people with ME/CFS are treated by many health professionals and medical researchers. There is a large and influential group of psychiatrists that posit that the disease is caused by nothing more than the belief that you have a disease. This is why there is seemingly an intense backlash against psychiatry and a frantic hunt for biomedical proof in ME/CFS.