After being on erfa thyroid for around 8 months I switched to a T4 + T3 combination about a year ago. I gradually increased the T3 and decreased the T4 over many months, the last dose I was ok on was 40mg T3 and 75mg T4 over the summer though my TSH was suppressed as it has been for years.
When at the end of last August I changed to 40mg T3 and 25mg T4 and for the first time since I was 6 years old my T4 bloods level was out of the lower range (which I know shouldn't technically be relevant...) I developed pain and discomfort in my lower arms wrists and hands.
At first I assumed it was RSI/tendonitis as I'm a violinist but after 3 months of complete rest, strong anti inflammatories, splints, physio and regular icing it had only gotten worse and I was unable to wash my own hair/dress myself and even holding a fork or a cup was too painful. I also had to stop going to uni as I'm studying violin and have been unable to play for months, and couldn't even hold a pen to write my essays.
I then thought back and noticed it had gotten worse when at the end of October (about 3 weeks after the pain began) I took out the T4 altogether and was on only 50mg T3.
In mid december after noticing the possible connection I went back to my previous dose of 40mg T3 and 25mg T4 and my hands improved slightly but were still bad and I developed pain in my legs too. I saw my endo at the start of Jan and we decided to gradually up my T4 to 75 and T3 down to 30mg. When I increased my T4 to 50 it improved a lot, then a week later when I increased to T4 75 the pain/discomfort was improved again, though it is still there but around 60-70% better than it was on no T4.
Any logical explanation for this?! I certainly can't think of one!