Some patients with Graves' or Hashimoto's disease also have a tendency to certain kinds of tendon and joint inflammation. Painful tendonitis and bursitis of the shoulder, for example, was reported in 6.7 percent of patients but occurs in only about 1.7 percent of the general population.
Rheumatoid arthritis is a more serious disease, in which there is a symmetrical inflammation of many joints of the body, most typically the knuckles, wrists, and elbows. It is also characterized by joint stiffness that is most severe in the morning. Severe rheumatoid arthritis appears to be only slightly more common among patients with thyroid dysfunction than in the general population. If you have hyper- or hypothyroidism you may notice mild morning joint pain and stiffness.
If so, like patients with rheumatoid arthritis, you can benefit from treatment with heat, aspirin, and related drugs. On the other hand, some hypothyroid patients have joint pain and stiffness that improves when they are treated with thyroid medication.