I presume that you are undertaking treatement from a Psychiatrist curently. If not, kindly consult with one.
Secondly, to answer your specific question about there is a permament cure for ADHD, I would say the following:
Like for any other psychiatric disorder, no Psychiatrist can guarantee a cure. But the good thing about ADHD is, the fact that with right treatment, the afflcited individuals lead as normal a life as any other person, in fact better than some, in some regards. I have had colleagues with adult ADHD, who are doing wonderfully well in their professional lives.
Also, since your son is only 4 years old, you have spotted the symptoms early and that is very good. Earlier the detection, better the response to treatment interventions.
Therefore. I suggest you to take your son with a Child Psychiatrist of your choice, who would prescribe not just medication, but also behavioral techniques which would help in the long run.