League has blocked global hoykeys (eg: music players like iTunes/Winamp) since 2009.

http://forums.na.leagueoflegends.com/board/showthread.php?t=30524&page=1

Only keyboards with dedicated media keys will work, and even then, only sometimes. Custom hotkeys (eg: ctrl+alt+arrow keys) have never worked. There is a fix at the very end of that thread using autohotkey. But with the new anti-cheat stuff live, who knows. That might not work (or might get me banned). Why has this not been addressed in almost 10 years?