Yes, it is possible. In fact, a person can have both MG and MS.

If your husband has had an MRI, the doctor should have been able to tell if it is MS. Not always though. Sometimes MRIs get misinterpreted, or the signs of MS don't show up.

Dry mouth isn't a typical symptom of MS. It's often related to a medicine the person is taking. It can be caused by mouth-breathing too.

I have dry mouth but it can be managed with one of the oral moisturizers that are on the market.

I hope your husband will be able to find out the cause of his symptoms soon.