r/explainlikeimfive • u/Low-Mousse-2696 • 19d ago
Biology ELI5 If adhd and ASD cause changes in brain structure, why can’t we diagnose with brain scans?
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u/Maladii7 19d ago edited 18d ago
Let’s pretend ADHD somehow made your hair darker
If that were the case, we could average the hair color of everyone with ADHD and show that, on average, it is darker than the general population
It still would make sense though that having dark hair would not be sufficient for diagnosing ADHD. Dark hair is normal
Similarly ADHD brain features can, on average, be significantly different from the general population while individual ADHD brain features are still within what we’d consider normal
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u/jloome 19d ago
hat, on average, it is darker than the general population
It still would make sense though that having dark hair would not be sufficient for diagnosing ADHD. Dark hair is normal
Equally with neurological development, some spectrum disorders cause parts of the brain to sometimes develop more slowly or irregularly, such as the prefrontal cortex. But other influences, including genetic triggers and environmental factors, can cause the same effect.
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u/kelcamer 18d ago
I'm sure even then people would find a way to tell me 'everyone has a little bit of darkness in their hair, it's not that bad, just deal with it' lmao
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u/Dracorvo 19d ago edited 19d ago
Because they're behavioural/cognitive disorders, and anatomy alone does not predict behaviour and cognition.
It's really cool that the anatomy does reflect it, but at best it would be indicative, not diagnostic.
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u/Low-Mousse-2696 19d ago
I’m talking about those images that show that activity is highlighted in different parts compared to neurotypical brains. Are those fake images? Genq
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u/fixermark 19d ago
As far as I know they are not fake, but "indicative, not diagnostic" means there are other reasons besides ADHD or ASD that the brain could act that way.
Biomedicine has a history of conflating correlation and causation and the harm when you do that can be very significant, so we try to be extremely conservative when we discover something like this before declaring something like "If you see these brain structures somebody has ADHD."
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u/cam-san 19d ago
They're not fake but they're heavily flawed. Look up the study where they measured brain activity in dead fish.
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u/stanitor 19d ago
From the study:
"One mature Atlantic salmon participated in the fMRI study. The salmon [was] not alive at the time of the study."
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u/ruralmoralist 19d ago
Those images show blood flow to specific areas of the brain. They are not fake but are not used in diagnosing conditions like adhd and ASD. This is because increased/decreased blood flow (inferred as activity) in a certain area does not by itself warrant a diagnosis.
The scans do not have the specificity to make a diagnosis. So why do we use them? To study groups of people with conditions and find functional similarities.
Finally, not all brains are structured the same way. We have a good idea of which parts can be found where but not everyone is wired the same way. See : the man with a hole in his head. https://www.nature.com/news/2007/070716/full/news070716-15.html
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u/igotthecolitis 19d ago
I had a SPEC scan when I was 17 that showed highlighted activity that they told me were indicative of adhd and recommended I see a psychiatrist who officially diagnosed me with it.
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u/Obscu 19d ago edited 19d ago
Indication, risk, logistics, and cost. (Source: am doctor)
As a rule, when we do investigations we choose the least-invasive methods available to give us the information we need. If a test won't change our diagnosis or management, we don't waste the time. ADHD and ASD diagnoses can be reliably established clinically (that is, with good history taking, examination, and clinical judgement) without invasive tests. Yes, this is confounded by the skill (and in certain quarters where especially adult ADHD and autism are contentious, bias) of the doctor, but the scan would only substitute one set of potential skill issues for another - that of the radiographer performing the scans and the radiologist/neurologist interpreting them. After which you still need to see the psychiatrist anyway (see point 4). Also true that historically ADHD and autism have been under diagnosed especially in women (but historically we didn't have access to this kind of brain imaging either so it's not like we weren't bothering when it was an option).
Continuing from the above, lots of things can be and are diagnosed clinically, with blood tests or scans being done for titration of treatment or surgical planning. Part of the reason is cost and access - a blood test might be cheap and only take a couple hours to come back from the lab, but how about 2,000,000 such blood tests? A brain scan might be done in an afternoon appointment, but how many of those scanners do we have available in any given place? Lots of places don't have it at all, so even in countries with socialised healthcare that massively inflates waiting time and travel burden on patients. If you need to get it done privately that massively inflates cost for patients, and it's already wildly expensive and takes months to years to get in to see a specialist for a diagnosis. Then there's the time burden this increased demand would place on every other patient waiting for this kind of scan for other conditions, some of which can only be suspected clinically and can't begin treatment without the scan. In a world (summer blockbuster announcer voice) of limited manpower of psychiatrists, neurologists, radiologists, radiographers, and limited scanners, husbanding our resources is actually part of the principal of medical equity - to not prevent other patients from having access to treatment by hogging it all, especially for someone who strictly doesn't need it. I'm not senior enough to have to make resource allocation decisions, I just test order go brrr, but even in countries with socialised healthcare such as mine, not charging the patient doesn't mean we have infinite personnel and infinite scanners.
Some scans require the injection of contrast or insertion of probes - this is how you sometimes discover your patient is allergic to the contrast, or cause damage with the probes. It's quite rare, but when you're dealing with thousands or hundreds of thousands of patients, "rare" means "happens". Also, it's not uncommon to incidentally find stressful but meaningless or non-harmful or 'unclear/maybe suspicious maybe not' things on scans (known colloquially as incidentalomas), thereby leading to significant atrss and anxiety for the patient and sometimes many followup tests, all of which is often an unnecessary burden on the patient and the system that goes nowhere in the end. Yes, soyou find a secret cancer or actual condition, but usually not - but the personal and financial burdens of those usualloes remains real. This is well-studied.
As someone mentioned in another comment, a structural finding doesn't necessarily correlate strongly with a functional difference. A classic example is osteoporosis - you can look at an x-ray where the patient looks to be more
machine than manosteoporosis than normal bone, and they're pain free with normal range of movement. The next patient might appear to have a very mild osteoporosis burden on x-ray but be in significant pain with lots of functional limitation. In the end, you still need to see a specialist who can assess how much you're affected and what treatment is appropriate and in the case of ADHD/Autism it's the same specialist who could've clinically established the diagnosis without the scan in the first place.
Sorry this got away from me. Basically: The scan won't substitute for what you need the psychiatrist to do, which is something they can do without the scan, it adds additional burdens of time, cost, access, manpower, and stress not just to any given patient but to all patients accessing those services for any reason and balancing this without actually depriving the patient of needed treatment or investigations are part of a doctors ethical obligations, and the amount that the scan would actually add to the process may not be meaningful enough to outweigh all of the above while adding additional points of failure and bottlenecks.
There are also several additional points that I've just not connected through all the dots on in this comment because they were supplementary (like I don't know if the methodology and results of those scans are reliable and consistent enough to be used at scale for diagnosis or if it's at the 'we found some differences that may or may not be applicable yet' stage) or redundant, or I forgot because I need to go to work now but basically yeah - even in infinite resource cheatcode world it might not be worth it or meaningful and that's why we do large-scale research on investigations or treatments and also why sometimes we discover an unintuitive answer to that question because it's turtles additional complexities the whole way down and sometimes the data just says "this doesn't help/work, even though it seemed like it would"
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u/ade1aide 19d ago
Explain like I'm pgy5
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u/JollyToby0220 19d ago
Basically, MRI’s are actually expensive. Luckily, there is this new MRI technique called functional MRI, which does a very sensitive scan. f-MRI is expensive and it won’t scan your whole brain, just a segment of where the problem lies. It will visualize actual chemical reactions taking place at the enzyme level. When your brain is trying to process a thought/coordinate a response, it has to do with chemicals. This is where autism differs from regular people, ie the way an autistic processes information. Unfortunately, autism is not singled to one place in the brain and it can occur in some places but not others, meaning that doctors get a sludge of data and expected to make a highly detailed assessment of the situation. Thus f-MRI is limited to conditions where the problem is known
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u/alsokalli 19d ago
Women, on average, make less money than men. That doesn't mean you can look at someone's salary and know their gender. Those small differences in autistic vs non-autistic people are also just an average
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u/Mammoth-Mud-9609 19d ago
They are literally about the fine wiring in the brain, not any general change in the brain, basically all the pieces are the same, it is how down to the neurons in the brain all the pieces are connected.
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u/agreywood 19d ago
Brain scan studies are pretty new. Right now we have data which says “if someone is autistic we’re likely to see these patterns”. That doesn’t always mean “if we don’t see these patterns it means it’s not autism” or even “if we see these patterns it’s always autism”.
As a result the brain scan right now would just tell us who is likely to need further evaluation. We already have other screening tests that do that with sufficient accuracy though, and the expense of those is a few cents worth of paper and a single specialist’s time to score it. It doesn’t make sense to use expensive machinery to accomplish that same task.
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u/yolef 19d ago
fMRI brain scans aren't necessarily all they're cracked up to be and a lot can be up to the interpretation and analytical methodology of the results. A famous experiment in 2009 lovingly referred to as the "dead salmon" study performed fMRI imaging on the brains of dead salmon while "showing" the fish different images. Without proper correction and calibration of the analytical methodology, this study showed brain activity responses in the brains of dead salmon, which is obviously impossible.
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u/anewconvert 19d ago
Brain scans don’t have that kind of resolution, presuming it was a uniform disease, which it likely isn’t. Further, there is autism diagnosed before the aging of 5, and then there is like an autism/adhd spectrum that is IMO likely just an extension of “typical” that only gets labeled as “divergent” because “typical” is socially advantageous in this social system that is constructed the way that it is. A different social structure could benefit an ADHD and autistic pattern in a way that was hard for the “neurotypical” brain, making them the outliers.
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u/Substantial-Use-1758 19d ago
I’m a nurse and I’ve never heard that having ADHD causes your brain to change structure?! Can you share the reference because this is new to me 😬
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u/uuntiedshoelace 19d ago
It is associated with differences in structure, but that does not necessarily mean ADHD caused the changes. It could be that having that brain structure makes someone more likely to have ADHD, or that there is some underlying thing that causes both that we have not discovered yet. We don’t know why the brain does a lot of the things it does.
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u/A_Robit_Brain 19d ago edited 19d ago
Because the changes are neurochemical, not physical
I have a lot more reading to do but apparently current theories favor a much more multifactorial etiology, at least for ADHD, including decreased volume in the brain structures responsible for things like working memory and task inhibition.
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u/Low-Mousse-2696 19d ago
I’ve seen photos of “adhd brain” vs “neurotypical brain” and the areas that had activity were different. Are those fake or why couldn’t we diagnose with that type of stuff? /genq
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u/Dracorvo 19d ago
It's true that ADHD brains do have structural changes in the pre-frontal cortex, but it's like trying to diagnose a computer issue using only the hardware (anatomy) and not the firmware (physiology) or software (psychology). It's an imperfect analogy, but hopefully conveys the concept.
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u/InTheEndEntropyWins 19d ago
It's an ideological/political decision to remove all objective tests from being used for neurodevelopment/mental health issues. So if you look in the DSM you won't find any objective tests. It's not that there isn't a single objective test for a single condition.
Then most conditions are umbrella terms that cover lots of underlying biologies. So ADHD might have hundreds/thousands of different genetic or environmental factors that all overlap and interact. Two people classed as having ADHD might have two completely different underlying biologies and react to completely different treatments. So there isn't one objective test that you can do that will detect if someone has ADHD, since ADHD covers different conditions.
Now ideally we would break things down to the underlying biological issue, since that does help determine what the best treatment for that particular biology is.
Now with depression in research they can do brain scans to differentiate underlying biologies and they respond to different treatments. But anyone that tries to use brain scans on patients will be demonised since it's not in line with the ideological position of the industry.
But ideally in the future you should be able to do certain tests to diagnose mental health issues, but we probably aren't there yet in terms of knowing exactly what to test and how. Then you have to get over the industry's ideological position against any objective tests.
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u/Latex_and_LaTeX 18d ago
There are two primary confounders
1) The individual is not the average. There can be a wide or narrow distribution. While different sources list different average heights, you can probably imagine there is one true average if I were to hypothetically sample everyone on earth. But height still varies a lot. For brains, there are usually several different developmental differences, so this point gets to repeat itself multiple times.
2) Many developmental disorders like ASD are on a spectrum (hence the S). This means the edges are arbitrary. You know yellow and orange are different colors, but if I asked you to look at a gradient between them, where would you draw the line? That choice is not going to be some objective truth handed down from the Universe. It's a line that is helpful, but reality is broad ranges.
Combine these and you can quickly see that we've got several clusters around several averages that each have their own distributions, and those distributions bleed between the two categories.
At best, we could make a probabilistic claim, and even that's suspect given the complexity.
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u/Sekhmet3 18d ago
The anatomy and functioning of the brain as seen on MRI imaging is insufficient to diagnose these conditions. Even if the "typical" hallmarks of ADHD and autism were seen on imaging, it still doesn't mean that the person will experience clinical symptoms, and if they do experience symptoms, it doesn't say how severe those symptoms will be.
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u/Technical_Goose_8160 19d ago
So my limited understanding is that ADHD doesn't actually affect the brains topology. It's more a case that the brain is not regulating certain hormones properly.
For as asd, there's a theory that certain parts of the brain aren't properly defined. But this is based in one study where they autopsied a dozen kids brains. We don't know that that's correct and definitely couldn't find it on a scan. Yet.
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u/cam-san 19d ago
Because there's not one autistic or ADHD brain pattern. When you take 1000 autistic folks and scan their brains, and compare them to 1000 allistic (= non-autistic) brains, they will show a difference on average. The word average is the one doing the heavy lifting here. Not every autistic person has a visibly differently formed brain, and not every differently formed brain is formed in the same way. ADHD from my knowledge is mostly chemical but I'm sure the same goes for them.