Did it get an unusual amount of sun? I don't know about the whole plant, but is it like in a window where it could have gotten burnt?

Thanks for your reply. I don't think so - its about fifteen feet away from the window so I don't think its burnt...

Could it be some kind of root damage? has it been overwatered, etc? or have you sprayed something that has pooled on the leaves for a while? Is it on new leaves only, or older ones? It might need to be repotted.