Researchers Find Correlation Between All Types of Thyroid Disorders and Myasthenia Gravis

Researchers have found a correlation between all types of thyroid disorders and myasthenia gravis, particularly in women and older men, a study reports.

The research, “The Concomitant Association of Thyroid Disorders and Myasthenia Gravis,” was published in the journal Translational Neuroscience.

Surprisingly, the first study suggesting an association between autoimmune thyroid diseases, or ATDs, and myasthenia gravis stretches all the way back to 1908. The scientist involved, Dr. G.E. Rennie,  discovered a link between MG and Graves’ disease, a type of ATD.

Studies since then have generated conflicting results. Some have reported no evidence for the association, while others have reported high correlation levels.

A study that supported the correlation demonstrated that thyroid disorders occurred much more frequently in patients with MG than in people with other autoimmune conditions.

Researchers at Taipei Medical University Hospital hoped to come up with a definitive answer on a correlation.

There are three major types of autoimmune thyroid diseases. One is hyperthyroidism stemming from Graves’ disease. Another is hypothyroidism due to Hashimoto’s thyroiditis. And the third is euthyroid that stems from thyroid autoantibodies.

Researchers scoured Taiwanese Bureau National Health Insurance records from 2000 to 2002 to find patients with thyroid disorders and patients with myasthenia gravis. They found 520,628 people with thyroid conditions and 7,965 with MG.

A comparison of the records showed a significant association between the two kinds of disorders. The correlation was highest for Graves’ disease, which is also known as diffuse toxic goiter: 4.37 percent of those with the disorder had myasthernia gravis. Other correlations were nontoxic nodular goiter, 1.46 percent; simple goiter, 1.19 percent; chronic lymphocytic thyroiditis, 0.60 percent; thyroid cancer, 0.34 percent; and toxic nodular goiter, 0.25 percent.

In all of the associations, women had a significantly higher correlation rate than men.

Scientists use Q values to characterize the strength of an association between two diseases. A Q value of greater than 1 indicates a significant association between two disorders.

Researchers reported a Q value of 30 in men with chronic lymphocytic thyroiditis and MG. Other Q values were thyrotoxicosis, 13.3; acquired hypothyroidism; 12.7, thyroid cancer, 12.4; and simple goiter, 12.2. All were considered high correlations.

The team reported intermediate correlation levels between women who had thyroid disorders and MG. The thyroid conditions that fell into this category included toxic nodular/multinodular goiter, chronic lymphocytic thyroiditis, simple goiter, and non-toxic nodular/multinodular goiter.

The bottom line was that the researchers found a correlation between all thyroid disorders and MG. They also found a higher association between ATDs and MG in women and a higher correlation between the diseases in older men.

The co-existence of the disorders indicates that autoimmunity plays a role in the development of MG, they concluded.