It's a pretty common side effect of Topamax that it interferes with your ability to remember words. I quit taking it for that reason. I write for a living, and the ability to recall words became more and more difficult for me, interfering not only with my ability to converse with people but also my ability to write.
I've been off it for several months now, and though my word recall problem has improved somewhat, it hasn't gone away. I'm beginning to think that topamax damaged my brain permanently.