My Son,30 Years Of Age ,had A Shwanoma Removed From

My son,30 years of age ,had a shwanoma removed from C2 to C5 area in 2009 .He has weakness to his lt upper arm because one nurve had to be compramised.His last MRI in july this year shows that the tumur has grown back 3cms and has to undergo another surgery to remove that.
Recently,he is experiencing,shivering or shaky tremor like movement on his week hand above elbow level ,more when he plays key board and he cant control fingers.
Could someone explain this ,why and remedy
Thank you'
Molly.