titterbug,
I put down a link below that I had bookmarked. Since you're in Canada is this a greenhouse grown plant? I know you said stems (plural) but is there only one plant of one variety with this condition? Anyway, there should be some help by comparing the pictures on the link.

Here is a link that might be useful: http://aggie-horticulture.tamu.edu/tomatoproblemsolver/index.html