Hello ! I read your question and understand your concern . A brainstem tumor can cause different symptoms , like troubles with swallowing, breathing, spastic paralysis of four limbs, imbalance and problems with the gait, double vision , facial numbness, loss of hearing , raised intracranial pressure causing headaches and loss of vision etc. I think that the muscle spasms when he walks are related to the spastic paralysis from the brainstem involvement from the tumor of from the brain damage from high intracranial pressure (you refer that he has a shunt for this problem). This is a very common symptom in cases like this . I don t think that the muscle spasm are related to any medication. So I would recommend a lot of physiotherapy and stretching for the muscles. Baclofen would be very helpful if the pain is severe and the muscular contractions are interfering with his daily activity. Hope to have been of help! Best wishes, Dr. Abaz Quka