Suggest Treatment For Weakness In Left Arm And Shoulder

My husband has been experiencing weakness in his left arm and shoulder for close to two years. The muscle appears to have atrophied as well. Prior to that he has had pain in his neck and both shoulders for 10 - 20 years. He had back surgery about 10 years ago, but that did little to ameliorate the pain. A couple of months ago he went to an orthopaedic surgeon because he thought he might have a torn rotator cuff. The MRI showed no tear, only a little arthritis and inflammation. He then had an EMG and the neurologist recommended an MRI of the neck, believing that the current problem could be related to the back surgery. He also had 5 or 6 therapy sessions which provided no relief and only increased his arm strength minimally. Today he had an appointment with a neurosurgeon to review the results of the latest MRI, and she said that there didn t appear to be any real issues with the spinal column or discs. She prescribed a brain scan. My question is: Is there anything besides ALS which could be causing my husband s pain and shoulder weakness? We have both been researching on-line and have made ourselves sick with worry. I know you can t provide a diagnosis, but I d really feel better if there are other possible causes for his condition.