I am sorry to hear about the rough time your husband is having... I am a patient myself but this is what I know.
It is very typical to use the steroids and high dose steroids to reduce swelling. Some people don't have many side effects while others are effected greatly and sadly it cannot be predicted.
The steroid is temporary (they should tell you that) and he should taper off in a bit. I don't know why they can't find another pain med to help, there are other options... Does he have allergies? Is there an option to see another pain place?
There is also a special psych doc that specializes in brain patients, a neuro psych I think it is, and they can help a bit more than a regular shrink as they understand the physical reasons why your hubby is feeling the way he is as well as the stress of the illness... I would press for a referral to one of those and maybe he can add (or subtract) meds to get your husband feeling better.
Post back and let us know how he is doing.