What Causes Numbness In Arm?

My husband has lost use of his right arm, he woke up with a numb hand last week and it has spread to the whole of his arm. The amount of numbness varies, he has strength but no feeling. He has been having a tremendous number of migraines, up to 4 a day, we think due to changing weather here. Could this be migrain aura he is suffering? if so will the feeling come back?. He is being referred to a neurologist.