A close link between systemic arthritis and autoimmune thyroid disease exists. Because symptoms of arthritis are common in autoimmune hypothyroidism, joint pain has long been listed as a symptom of hypothyroidism. Some researchers are questioning whether hypothyroidism is responsible for arthritic symptoms and suspect that these symptoms may be caused by other co-existing autoimmune rheumatological conditions. Another theory is that thyroid autoantibodies are responsible for rheumatologic symptoms. This is supported by the fact that antibodies to thyroid hormone are commonly seen in autoimmune rheumatological disorders.
Symptoms
Patients with autoimmune thyroid disorders, more often Hashimoto’s thyroiditis but also Graves’ disease, often have rheumatic manifestations including a mild non-erosive variety of arthritis, polyarthralgia (multiple joints affected), myalgia (muscle pain), and sicca syndrome without a true Sjogren’s syndrome.
Thyroid Autoantibodies and Antinuclear Antibodies (ANA)
Besides TSH receptor antibodies and antibodies to thyroglobulin and thyroid peroxidase, patients with autoimmune thyroid disorders may also rarely have antibodies to TSH, T4, and/or T3. These antibodies are suspected, and subsequently tested for, when laboratory results are erratic and do not correlate with symptoms or other thyroid function tests. For instance patients with T4 antibodies will have elevated FT4 levels with normal TSH levels and no symptoms of hyperthyroidism.
Because of the many overlapping symptoms, patients with connective tissue disorders often have thyroid function tests. In a recent study, Italian researchers studied blood samples from patients with autoimmune thyroid diseases, rheumatoid arthritis and Sjogren’s Syndrome collected over the course of the past 30 years. They found that patients with rheumatoid arthritis and Sjogren’s syndrome were more likely than patients with Graves’ disease or Hashimoto’s thyroiditis to have antibodies to T3 and T4 and less likely to have thyroglobulin antibodies.
Patients with the autoimmune thyroid disorders were less likely to have antibodies to T4 and T3 but more likely to have thyroglobulin antibodies. In addition, patients with autoimmune thyroid disease often have positive tests for antinuclear antibodies.
Studies suggest that there is a close connection between the proteins that the immune system targets during the development of both the rheumatological and autoimmune thyroid disorders.
Overlap Syndromes
Just as there are overlapping autoimmune liver diseases, such as autoimmune hepatitis and primary biliary cirrhosis, and an overlap between systemic lupus and undifferentiated connective tissue disorders, some researchers suggest that there are overlapping thyroid and rheumatological disorders that may elude a definitive diagnosis. It’s suspected that patients with joint pain that occurs when thyroid hormone levels are low may be expressing latent conditions of rheumatoid arthritis or undifferentiated connective tissue disease. This theory would explain why not all patients with hypothyroidism exhibit joint pain. This theory also explains why joint pain can occur in patients with thyroid antibodies who are euthyroid.
Mosaic of Autoimmunity
Many of the autoimmune disorders are characterized by inflammation along with the production of various autoantibodies. In addition, many autoimmune disorders are triggered by genetic, immunological, hormonal, and environmental factors. The interplay between these disorders is referred to as the mosaic of autoimmunity. The term mosaic refers to the diversity of symptoms and manifestations among people genetically predisposed to autoimmune diseases. This concept is sometimes used to explain the fact that thyroid and antinuclear (ANA) autoantibodies frequently occur in both rheumatological and thyroid disorders. This would also explain the arthritic symptoms that frequently occur in people with thyroid disorders.
Studies in Children
Because of the appearance of autoimmune thyroid disease so often seen in patients with systemic autoimmune diseases such as systemic lupus erythematosus, Sjogren’s syndrome, and rheumatoid arthritis, Bulgarian researchers conducted a study to assess the frequency of thyroid antibodies, thyroid inflammation and thyroid lesions in children with rheumatological disorder. The results showed that 44 percent of children with juvenile arthritis had thyroglobulin or TPO antibodies. Of these children with thyroid antibodies, 85.2 percent were euthyroid (normal thyroid function, 11.1 percent had compensated hypothyroidism, and 3.7 percent had hashitoxicosis.
Resources;
Rugger, R.M. Galetti, M. and Aragona, P, Thyroid hormone autoantibodies in primary Sjögren's syndrome and rheumatoid arthritis are more prevalent than in autoimmune thyroid disease, becoming progressively more frequent in these disease, Journal of Endocrinological Investigation ISSN 0391-4097 CODEN JEIND7, 2002, 447-454.
L. Punzi, and C. Betterie, Chronic autoimmune thyroiditis and rheumatic manifestations, Joint Bone Spine, July 2004l 71(40L 275-283.
Miailova D, Grigorova R, Autoimmune thyroid disorders in juvenile chronic arthritis and systemic lupus erythematosus, Adv Exp med Biol, 1999L 55-60.
Elaine Moore - I'm a retired medical technologist and medical writer with more than 30 years experience working in hospital laboratories. Currently, I ...
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