I feel like I've identified a few fatal issues with the diagnosis process/DSM-5 that keep medical professionals from diagnosing Neurodivergence and personality disorders.
I can only speak for my experiences with ASD, ADHD, OCPD, OCD and NPD, but I'm sure these problems also happen when trying to seek diagnosis or talk about traits associated with ASPD and BPD as well.
These disorders heavily impact each other and change the surface appearance of how each disorder represents to the public/to medical professionals: My ADHD and dyslexia makes (for me) being an OCPD perfectionist impossible. I hate minute details. I often struggle to look an email over long enough before sending it. This doesn't jive with many professionals' opinion on what OCPD is supposed to look like. If you're not a perfectionist, and you don't agonize over an ever tightening spiral of details before putting a plan into action, it can make it look like you don't have OCPD. Some people's ADHD enforces their need to triple check everything and make sure it's "perfect" because they have trauma around always messing things up because of ADHD. It's such a mixed bag.
Along these same lines, ADHD and a love of attention and public affection I feel from what I associate with narcissistic tendencies makes my autism very hard to recognize. I love talking to people and touching people and being touched (in non-sexual, friendly ways) which muddies the waters further, and ADHD makes me chatty and risk-taking, further dragging the stereotype away from ASD. I could go on and on, but you get the idea. All the disorders impact and change and mask each other. I know this because I've lived with them for almost 5 decades. The 26 year old clinician covered by my insurance who does not have these disorders and is going off a checklist will mark me down as not having OCPD or OCD because of this. If I hadn't brought in a 7 page, single spaced document outlining all of my ASD symptoms for my assessment, that might have gotten missed too.
I recently spoke to the daughter of a friend who got a "Close, but it's not ASD" opinion from her ASD assessment, but when we talked about ASD traits and how they mixed with ADHD (she has both) she was like YES YES THAT'S ME I AM AUTISTIC. She got missed. A lot of us do. I told her, next time, write it all down, or they won't believe you.
Masking further muddies the waters: I am a very, very high masking individual across all my disorders, and I'm not alone. Early on, I realized that to be considered likable and to make friends (two of my main goals in life), I needed to rigorously mask any and all things about me that made me unlikeable or unpleasant to be around. This is why I only truly show my OCPD side to those that are a) very close to me and b) prove to me that they won't leave me if I get disrespectful/phobic/controlling/hyper anxious etc. It's why I pretended to be OK with boundary violations in social and sexual situations. Why I struggle greatly with confrontation, and why I have rigorously developed a charming and carefree social persona that hides a massive plethora of anxieties and compulsions. Doctors see this persona and express doubt about me having these conditions, which is very upsetting.
Although online sources confirm that you can have mild, moderate or severe versions of all disorders (personality or otherwise), I've heard doubt expressed repeatedly about my having these disorders because I am not some awful, tyrannical monster that is difficult to be around all the time: Also, if I suspect I have OCPD or NPD (even if it's a mostly non-perfectionistic expression of OCPD and a mostly non-toxic representation of NPD) then I can't have it. I can't count the times I've heard people online say some version of "you can't have narcissistic traits or OCPD and be a nice person or be aware of it." These blanket statements feel the same as "you can't have autism and have friends." People are very black and white about these disorders. Probably because only very difficult people whose lives are deeply negatively impacted ever figure it out and seek treatment. I also get it that tests for disorders are made up of criteria that's meant to screen folks out if they don't reach a certain threshold, but stating that I just CAN'T have a disorder if I am also aware that I have it is ludicrous.
I know we're in the beginning of opening up about mental health, and that there will be a DSM-6 and 7 and 8 probably that will more accurately diagnose people, but the traits of OCPD, OCD and NPD that I've recognized are pervasive in all my thoughts, actions and motivations. This stuff wends its way through my entire life and informs many of my decisions. Just because that's not always visible on the surface, doesn't mean it's not there.
I have multiple unkind, anti-social, self centered and controlling urges daily that I relentlessly suppress, because I know they are wrong, and so I can have the pleasure of connecting with other human beings. When I go to seek treatment to try and lessen the internal and external impacts these urges and thoughts have on me, my life and on a few choice other people, I am gaslighted and told my own lived experience is null and void.
