What you describe is not Hirayama's disease. Hirayama only affects the hands as far as I know (from online research). Generally it only affects one hand, though a lesser effect can sometimes hit both hands. Legs are not part of this particular disease. What your brother has seems to be something else. I can't say much more, but hopefully closing this door will allow you to search for the true answer. I pray your brother gets through this with a recovery.