I would like to assess the symptom of neck flexure in PSP. The typical position repeated in most descriptions of PSP is "backwards" (called retrocollis). However, some have their neck "forwards" with chin on their chest (called antecollis, that is common in Parkinson's).
My wife's neck bends forwards and her chin often drops onto her chest. Diagnosed with PSP, she has very clear clinical (and MRI) signs of PSP and not Parkinson's, even though she has this antecollis.
Can you send a quick post about your loved one's neck position.