I have a vascular dementia, and your husband's symptoms do not resemble mine.
It could well be that his linguistic ability is somehow compromised. We are born with certain innate linguistic wiring (see N. Chomsky's writings). Do you think he gets distracted before he can finish saying or completing his thought. or does it sound like he just forgot what he wanted to say in mid-sentence. The latter sounds more like dementia, or an attention problem, but it just might be a mental, language structural problem of some kind. You could try to find a linguistic professor at a nearby university to ask for help, and he might have more insight into what is going on than an m.d.