Anotherwords, PD is lack of Dopamine. Schezophrenia is too much dopamine. If your husband was doing well on Sinemet (YOPD are more sensitive to Sinemet) why did the neurologist add Mirapex to the med list? This will make more dopamine available to the brain and if your husband is as sensitive to Sinemet as I am, He may be getting more Sinemet than he needs.

Doctors follow what is written in research. If research says to add a MAO inhibiter then thats what they do. Most neurologists start a patient newly diagnosed with Eldepryl, and wait as long as it works before adding Sinemet.
Sinemet has bad side affects after 20 years. At your husband's age time goes by fast. Maybe you might want to get a second opion if your current one is not open to discussing options such as taking him off Sinemet or putting him on Requip (another drug simliar to Mirapex but fewer people seem to suffer side effects.)

Keep in touch and let us know how both of you are doing.

Dianna