A while back, I ran across a post by Virginia Sherr, MD, a psychiatrist who also has Lyme herself, posting at TheHumanSideOfLyme [dot] net. Part of the post talked a bit about thyroid function in those with Lyme. Here's a bit:
"In my psychiatric office, I had been listening for years to a subset of patients who were exquisitely sensitive to everything chemical in their lives. Medicine that required a dosage of 50 mg for the average person was too strong at 12.5 mg for them. Any commonplace side effects were magnified, and therefore, the idea of taking medicine had become anxiety-producing to them and, I remember, to myself as well, for the same reason. ...
"It turns out that Lyme disease tends to interfere with the metabolism of the liver in such a way that chemicals are processed too slowly. And there is a failure of the 'T4 thyroid hormone' to convert properly into T3 hormone at the cellular level. [Lyme disease] causes a Wilson's syndrome -- a lowering of body temperature -- which makes all chemical reactions sluggish. This causes a backlog of molecules, which are imperfectly metabolized if at all and which then act as if the person has taken an overdose."
Interesting.