To me, theme is a broad category, and topic is quite specific. For example, my lessons in class this week focus on the theme of "Education". The topic for today's lesson is "Privatization of Education".

A topic is equivalent to a subject, and is often quite concrete. The topic of your discussion might be the unemployment problem, for example. A theme is much more abstract. You would say that there are several themes running through a film, for example, friendship and betrayal. You would say that the theme of isolation is common in a particular writer's work.

Let's have one illustrative example. "The topic of today's discussion is 'Primary School Education'. The theme if my paper is 'There should not be any exams'."

Good question Camilo, I think a theme is the idea or thrust of the story, while the topic is what the general story might be. Both are very close, but can be used in different situations. The topic of discussion is..., the theme of his music was...