Make sure those T3 and T4 thyroid hormones are FREE T3 and FREE T4.....
But if you have thyroid antibodies like most that lead to Hoshimotos or Graves disease, that would be the cause.
Important to get TPO, TgAb and TSI antibodies tested if your T3 or T4 thyroid hormones are abnormally low or high.
"So, for example, a C5 C6 disc that is herniated will affect the nerves that control the muscles in the shoulders, arms, hands, neck, as well as other areas of the body such as the head, eyes, ears, and thyroid gland.
Because of this, if there is any pressure applied to these nerves (whether it be from a herniated disc, or some other condition), it is very common that you will not only experience neck pain, but also symptoms related to these other areas.
For example, you may also experience arm pain, burning, numbness, weakness, headaches, thyroid problems, problems with your vision, ringing in the ears, etc." - C5 C6 Disc Herniated - Heal Your Bulging Disc