My husband died in 2019 from progressive supranuclear palsy. He was in Vietnam from 1963-1964, is this possibly from agent orange exposure?
There are many similarities between presumptive Parkinson's Disease and Progressive Supranuclear Palsy. However, VA does not recognize PSP as an agent orange presumptive disease. To establish service connection for benefits will require an Independent Medical Opinion from an expert disability physician.
Once the physician has established that the veterans PSP is more likely than not caused by agent orange exposure, a service connection is likely to be made. See this BVA appeal.
You can learn more about the IMO and meet the doctors I refer to here. Good luck.