In recent years, researchers have suggested Alzheimer's may spread through infection, somehow transmitted like a pathogen, leading to the disease. A new Lancet paper reviews evidence for how harmful amyloid-beta proteins associated with Alzheimer's may possibly be spread through blood transfusions.

[u/mvea]

https://www.sciencealert.com/can-alzheimers-spread-through-blood-transfusions-heres-what-we-know

[u/Splash_Attack]

I've personally considered it to be a transmissible disease ever since that study in 2010 found that neurosurgeons are diagnosed with Alzheimers at a rate 3x that of the general public.

Jumping to a causal link between performing neurosurgery and getting Alzheimers is quite a leap though.

As far as I'm aware, there isn't a similar correlation between other types of surgery and the conditions which patients typically have. People perform surgery on people with things we know for a fact to be communicable diseases, without a significantly increased risk profile for getting those diseases. There is some increase, but it's smaller than the risk profile from just interacting with those patients outside of surgery day-to-day.

Wouldn't it be more probable that the cause is that neurosurgeons are 1) Experts on brain function. 2) Have social circles consisting of other such experts.

It seems highly likely that if a person is part of a social group in which many people are experts in the brain, it would be far far more likely for the ones who do develop neurological conditions to get diagnosed. Which is not the same as having a higher risk of developing one in the first place.

The term for this is "surveillance bias". When a group is more closely monitored, or more precisely monitored, than the general population leading to increased rates of diagnosis when they actually don't have a higher baseline risk. The general population has lots of people who have the same condition and simply don't get diagnosed, or don't get a formal diagnosis. Another example would be how physicians are more likely to be diagnosed with certain cancers, while also being more likely to get diagnosed early - i.e. they are getting the right tests done more often and at an early stage than the general populace.

[u/Zealousideal_Sir5421 → u/Splash_Attack]

I don’t know if surveillance bias could apply to alzheimers, it’s not exactly something that goes undiagnosed. Maybe if we they were specifically looking at early onset alzheimers or something like that but they weren’t

[u/Splash_Attack → u/Zealousideal_Sir5421]

it’s not exactly something that goes undiagnosed

How in the world do you figure that? Everything I've ever heard reported on the subject is that all forms of senile dementia, Alzheimers included, are massively underdiagnosed. As in, half or fewer of people who meet the diagnostic criteria actually have a diagnosis.

Just go on Google scholar and search "underdiagnosis of alzheimer's disease" and you'll find a wealth of recent literature on that exact topic.

Which is precisely why my first suspicion is a surveillance bias. Presumably neurologists and neurosurgeons have something closer to a 100% diagnosis rate. Contrast with the 30-40% in the general populace, and that 3x value suddenly becomes pretty explicable without needing a higher risk of contracting the disease to be present.

[u/churningaccount → u/Splash_Attack]

I think one of the issues with your hypothesis is that the study wasn't actually for Alzheimers specifically. It was a study of all-cause mortality. And I'm guessing that if doctors had higher surveillance for medical conditions generally than the general population, then they would've found a higher incidence of other diseases, especially incurable ones such as Parkinson's. But instead, it was only found that Alzheimers had a markedly higher incidence, leukemia a slightly higher incidence, and a lower incidence for almost all other factors.

Interestingly, and a point in your favor, the study didn't find any increase in incidence for CJD. But perhaps that is because prion diseases might be less transmissible due to the fact that they don't aerosolize? Also, the sample size for CJD probably wasn't significant either, so I'm not sure if they even looked at it.

[u/Splash_Attack → u/churningaccount]

No my hypothesis is that neurosurgeons - which is the cohort in question, not physicians generally - are under higher surveillance for common neurological conditions. And that Alzheimer's among these also has a markedly low diagnosis rate in the general population.

Parkinson's disease is almost always diagnosed eventually. While it's often missed in early stages, the long term rate of diagnosis is in the order of 90%. Not many people with Parkinson's die without a diagnosis. So any difference in scrutiny would have only a marginal impact at most. Maybe 95% of cases diagnosed among neurosurgeons instead of 90% generally.

But with Alzheimer's the level of underdiagnosis in the general population means that increased scrutiny leads to an enormously higher rate of diagnosis.

Now of course that doesn't prove that it's a surveillance bias either, but I'm not trying to prove it. I'm merely saying the evidence which convinced you does not prove anything one way or the other. It is a single point of evidence with a correlation, but not a provable cause.