Brachial Neuritis...how do I prevent atrophy?

At 39 years old, I'm 4 days into acute brachial neuritis. I had it 19 years ago on the right side and the paralysis and atrophy in my deltoid persists. I still have not recovered full extension of the fingers on my right hand.

It has now presented in my left side and I would like to treat it differently. If i can endure the pain, should i aggressively exercise these muscles, rather than simply maintain range of motion?

Any suggestions would be appreciated.

Brian