[atiredturte]

> Why do we separate ADHD from other abnormality with similar symptoms, when ADHD itself seems symptom-based diagnosis?

What do you mean by symptom-based diagnosis? Most ailments are diagnosed by their symptoms. If you mean diagnosis by measurement of specific chemicals/etc in the brain, I've heard of some studies that show that you can diagnose ADHD through brain scans[1]. Just because there's symptom overlap doesn't make the diagnosis moot. Both allergies and the common cold can result in similar symptoms, yet we still diagnose them separately because they are not the same thing. Yes, depression and ADHD might have some similar symptoms caused by their own unique effects on dopamine in the brain, but they are both much more complex than that.

> I have my own personal hypothesis that some types of ADHD are caused by persistent stress due to sensitive sensory reactions

Given that ADHD has a very heavy genetic component, I am inclined to disagree. However, I did find a paper[2] that indicated a link between socio-economic factors and ADHD. The causation/correlation is not particularly clear in the paper, but it could be interesting to look at.

[1] https://www.medicalnewstoday.com/articles/315884.php [2] http://www.academicpedsjnl.net/pb/assets/raw/Health%20Advanc...