How can I get the neurologist to release Father's findings?

You can't actually do that on AC, I don't think - "like" your own comments. Try it.

Do you always respond like this to legitimate challenges? I wouldn't try that. Not in court, anyway. Not if you can help it.

At what point did you become aware of your father's plans to marry his girlfriend? Because either you had doubts about his competence then, in which case you ought to have challenged the marriage; or you didn't, in which case it is remarkable that all of a sudden you have now.

I'm so sorry you find it insulting, but if you think I'm the only person who's going to question your motives you are in for a shock. And, by the way, affluent people are by no means immune to avarice and vindictiveness - as I'm sure an experienced judge will know only too well.

Immediately see a lawyer and seek Guardianship if you think Dad is incompetent. Only a Judge can declare competency or incompetency.
I agree with others who suggest your father may have revoked your POA and HIPAA access. He probably also executed a new Will. You NEED a lawyer.

Um. Just looking at the timeline, there. Your father met his now wife fifteen years ago. Your father's GP referred your father to a neurologist one year ago. Your father married his girlfriend four months ago, but you didn't oppose the marriage on the grounds of his incompetence, did you? Since then he seems to have set about making provision for his wife's future security; and *now* you're concerned about his mental capacity.

You do see why people who've been closely involved in his medical care might wonder about your motives, and start behaving with additional circumspection?

To the outside observer, it is not irrational for a man in a 15+ year relationship to give thought to how to protect the woman he has loved for that long. Rather overdue, indeed, one might think. Marrying her is one way; reorganising his assets would be another. Is she fleecing him? Because I hate to say this, but it really does look more like you're concerned that she's "fleecing" you.

With all due respect, how do you know your POA is still in force? If your father wrote a new one you might not have been told.

My POA is fully intact. The doctor is reputable with 30 years experience. His failure to release medical records would only bring litigation and potentially be liable for failure to do so. Without question my father's dementia is getting worse and I need to know if he is still competent and aware of what he is doing.

I imagine your father removed his permission for you to receive information, it is probable he replaced you as POA as well. The neurologist doesn't want to be caught in the middle of a messy legal dispute, get your own legal counsel and ask them how to proceed, you may need to duke it out in the courts.