PSP is very rare and very difficult to diagnose, and is usually diagnosed in people who have previously been diagnosed with Parkinson’s or Parkinsonism.

The main differences between the two are eye contact and facial masking. Here’s a comparison:

https://www.mayoclinic.org/diseases-conditions/...

The big difference is that it progresses much quicker than Parkinson’s disease in fact it’s been called Parkinson’s plus. Also
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An overview:

https://www.ninds.nih.gov/health-information/di...