Secondary nocturnal enuresis is when a child has been dry at night for 6 months and then begins to wet again. Secondary nocturnal enuresis is easier to treat, because in most cases this is a result of a change in the child's life.
Identifying the change and addressing it will resolve the issue in most cases. The change may be situational such as a change is eating, drinking or sleeping habits.
It could be physical, such as the onset of diabetes or a urinary tract infection or it could be psychological such as a divorce, death, move, birth of new sibling etc.