Imam Ahmed has narrarted that Usamah bin Shuraik said that " I was with Prophet Muhammad ( P.B.U.H) that when Bedouins came to him and said ' O Messenger of Allah ( GOD ), should we seek medicine ? He ( Muhammad P.B.U.H ), 'Yes , O slaves of Allah (GOD), seek medicine, for Allah has not created a disease except that he has In addition created its cure, except for one illness.' They said.'And what is that ?' He said, 'Old Age." link to it ( Click here )
Reference " Ibn Hanbal 'Musnad' 1:377
So from this we can see that every disease has a cure for it in this world.