Hi and welcome to the Migraines & Headaches Community.
No diarrhea is not a typical withdrawal symptom for Topamax. However, every person is different so, it could be possible.
To be sure, I would contact your PCP and ask if it is anything to be concerned over.
I am unaware of any cases where it is related to Topamax withdrawal. However, it is a symptom which can and should be easily treated, to prevent dehydration.
Ask your doctor about taking MiraLAX (Polyethylene Glycol 3350) or some other alternative.