I Am Wondering If My Husband Has Onset Of Parkinson's

I am wondering if my husband has onset of Parkinson's disease. His right thumb trembles and he doesn't know it. I point it out to him and then he stops. It's been going on for about 9 months. Thirteen years ago he sustained a mild traumatic brain injury. Is this related? He had to quit work at age 57. I work and he stays home and does not do much all day. I have been having a hard time getting him to go to doctors. I think its because of his brain injury. Your thoughts on Parkinson's?