Why "a" vs "the" cause of Alzheimer's?

I describe my discovery as "a cause of Alzheimer's" rather than "the cause of Alzheimer's" not because I doubt that my discovery is the common cause of Alzheimer's, but because I am not in any position to rule out other causes. 

In such a case, to declare it a cause, rather than the clause, is simply to observe due argumentative caution.