[carld]

Thanks Alan, I dug up this bit with a quick search of Wikipedia "At the start of the novel, Dr. Butters asks Dresden if he is still having headaches."

That's not what I'm thinking of, however. At some point before, during, or after the final battle with the Skinwalker, Harry mentions that Joseph Listens-to-Wind (AKA "Injun Joe") helped him deal with his headaches.

It seemed to be a reference to past events and a tie-in to a short story or graphic novel or something like that. I was sure there was something there that I'd missed, maybe not.