I'm also in a Zone 5 climate but o the other side of the border.

I usually prune mine in the fall in order to get them inside. There is nothing saying that you have to prune it.

I would prune it only if you are unhappy with the shape of your brug.

:)

I agree with the previous post. Pruning new growth will set back flowering and you have a short season to begin with. Once you see where the new growth is coming from you can trim off the dead stems.