Aphasia is a fairly common symptom of Parkinson’s there is a loud program available for PWP. It is helpful for a full range of speech issues.
My twin brother has a Parkinsonian illness called PSP (progressive supranuclear palsy). He has severe aphasia from this, as well as bad balance, etc.
It sounds like almost any disease affecting the brain can cause some form of aphasia. When I first asked this question I halfway assumed it was MSA; now I know I have had 2 small strokes in just the right places so as to cause aphasia, yet so does the MSA. The brain must be like a vast canyon with all sizes of caves for problems to pop out of their hiding places.
It’s brutal on the psyche! Be patient with him! Oooorah!