Healing of diseases is done by medical institutions and yoga is not trying to take the place of medicine. Yoga doesn’t substitute medicine. Yoga is a system of self-exploration, which helps to maintain health and sometimes deals with certain diseases, but it is simply a side-effect of self-exploration process, no more than that. If you have any disease, it is necessary, first of all, to seek qualified medical advice!
Of course, there are situations when yoga helps to overcome health problems, that doctors were not able to deal with.