Unfortunately yes. It is a possible side effect or complication. And that's exactly what happened when I had botox injected into my urinary sphincter (bladder wall too). Though I don't know how they would handle that with the anus.
I'd say still go through with it too. You don't stop driving a car even though you could get into a crash. But you do need to be aware it could happen.
Do you think it could really cause the anus to seize up? I have never considered that at all. I really hope it doesn't do that. At this point I'm going ahead anyway. The good thing is that hasn't happened to the other person who had it done.
This is making me a little concerned because I just thought you were all talking about the urinary sphincter but if you think this can happen to the anus then I could have a problem. But I don't think it's likely??