Medicine & Research

MS and Autoimmune Thyroiditis

By Roger S. Williams, M.D.

Current evidence suggests that MS is an autoimmune disease. This means that tissue damage is not caused primarily by an external agent, such as a virus or toxin, but by the person’s own immune system. The immune system is our defense mechanism against the potentially harmful effects of other agents, either external or generated from within.

Our immune system, which is controlled by our genes, protects us by neutralizing potentially harmful agents, like bacteria and viruses. Our immune system operates through our cells, including T-cells, B-cells, and macrophages. These cells communicate through various chemical messengers, such as complement, interferons, and antibodies. Our immune cells and chemical messengers bind to sites on the harmful agent called antigens, sort of like a lock and key. But if the foreign antigen looks like a normal part of our body, such as myelin proteins for example, the immune system may mistakenly attack. This paradoxical damage of our own tissues by the activated, normally protective, immune system is the basis for autoimmune disease.

Some people are genetically more prone to develop autoimmune diseases than others. Currently, the genetic control of immunity and autoimmune diseases is a vigorous area of research. It is hoped that a better understanding of the genetic mechanisms of disease susceptibility will allow for the development of better therapies or means of disease prevention.

It has been observed that genetic susceptibility to autoimmune disease can result in a cluster, or an increased prevalence, that appears in some people and their families. MS and autoimmune thyroiditis are commonly seen together and there is also an overlap in symptoms, such as fatigue, weakness and cognitive slowing. Other autoimmune diseases that may be at least somewhat more prevalent in patients with MS are type I diabetes, rheumatoid arthritis, Crohn’s disease, Sjögren’s disease, psoriasis, vitiligo and uveitis.

A relationship between some treatments for MS and autoimmune thyroid disease has also been noted. Beta interferons (Avonex®, Betaseron®, Rebif®) and alemtuzumab (Campath*) increase the risk of thyroid disease in patients with MS.

It is good practice to check thyroid function as part of the diagnostic evaluation of anyone suspected of having MS, and to monitor thyroid function periodically during the course of the disease. More frequent monitoring of thyroid function is required in patients who are treated with beta interferons.

Dr. Williams is the Medical Director of the Northern Rockies MS Center (NRMSC), a division of St. Vincent Healthcare in Billings, Montana. He is a Fellow of the American Academy of Neurology and is certified as an MS sub-specialist by the Consortium of MS Centers. He has academic appointments at Montana State University and the University of Washington School of Medicine.

* Campath is an immunosuppressant used to prevent transplant rejection. Campath is being investigated for use in MS but safety and efficacy have not yet been established. It is not an FDA-approved drug for MS.

(Last reviewed 7/2009)