What is a thyroid disease ?Can it be cured permanently or one is required to take medication life long?

Is it a disease or a distubed gland condition which needs one time treatement or life long treatment? Can it be corrected for once and for ever with the modern day medicines? If not treated out of ignorance then what are the extreme harmful effects of the disease? Can any medical professional guide me about this disease as to help me approach the doctor to be guided properly to overcome the problem?