Hello – The more common situation is for agranulocytosis to occur during the first 90 days of starting (or re-starting) antithyroid meds, but we have seen a handful of individual case studies where this situation developed years later.
As far as I know, the concern with longer-term use of PTU is with a specific complication called ANCA-positive vasculitis. It’s rare – and is more commonly reported in individuals of Asian ethnicity and in children, but it’s certainly something to be aware of.
Hopefully, you will get some responses. We have this thread “stuck”, so I will put in a reminder in the main section.