It could be that you have a Parkinsonism other than Parkinson's Disease that doesn't respond to carbidopa because it isn't a dopamine issue. Is your doctor a Movement Disorder Specialist?

thanks Ginny for your input. we're going to see the neurologist tomorrow. I'm definitely looking into a movement disorder specialist

A MDS is someone with more training and knowledge in Parkinson's and Parkinsonism than a regular neurologist. You can Google it to find one who is local to you. If your husband has vascular dementia, that would explain why the PD drugs weren't helpful.

my husbands datscan did reveal parkinsonian syndrome. his dr is a neurologist. I'm not sure what a Movement Disorder Specialist is. He has PT 3 times a week. he was diagnosed with vascular dementia in 2017. he recently came off Sertralne which was a cause for Seratonin syndrome. the only dementia related drug he takes is Memantine. he takes no drugs for Parkinson's now. how do I research Movement Disorder specialists? google?