Will speech deteriorate over time?

I received this email earlier today:

“Mother seems to have all the major symptoms described with PSP except her speech. I can still understand everything she says easily (although her voice is weaker). Will this change over time too?”

Here’s my answer:

Probably though no one can be certain. People with the PSP-parkinsonism type of PSP don’t have dysarthria as a primary symptom. But these people often develop speech problems later on.

In a woman in our local support group who has PSP-P, her speech was understandable by me for the last couple of years. Now her voice has gotten so quiet that I can’t hear her, and no one else can either. She hardly speaks any more now.