How does your husband refer to his current issue? What interventions have his doctors recommend so far?
It’s a serious issue if he refuses to follow the management program because he thinks this is something benign that will just go away. If that’s the case, you might want to discuss the situation with the clinic social worker.
On the other hand, if he is willing to follow the doctors’ recommendations in terms of adaptive equipment, keeping up nutrition and calorie intake, etc., then it really doesn’t matter if he and you refer to it as ALS, PLS, or something else.
Hopefully it’s a matter of him needing more time to come around to accept the diagnosis. A lot of people, myself included, use denial as a coping mechanism. It can sometimes be healthy in terms of helping one get through the day without obsessing over the diagnosis and the future. It is often hard for people to believe that they have a serious problem when they can still function in some capacity.
I suspect he does believe the diagnosis on some level but is terrified.
He still needs to come around to some level of acceptance to get financial and legal affairs in order including documentation of his end of life choices. You could discuss this with him and tell him it’s a good idea no matter what is going on.
Hopefully other family members and close friends can help too.