Reminders are sent to your email address to make it easier to remember when to update your profile data (e.g., MonthlyMe, DailyMe, Treatments and Symptoms) at PatientsLikeMe. You can manage them under Account, under Email Settings.
Learn more about managing your reminder and email settings here: How do I change my email settings?
You can add forum threads to My Topics by using the Follow link at the top of the thread you want to remember. Here you can set an alert so you will be notified when someone replies.