Research suggests there is a link between hyperthyroidism and rheumatoid arthritis. However, the association is complex, and researchers do not fully understand how the two conditions affect each other.

Hyperthyroidism and rheumatoid arthritis (RA) have what healthcare professionals refer to as a bidirectional link. This means that having thyroid disease may increase a person’s risk of having RA. Conversely, it also means that having RA may increase their risk of having thyroid disease.

Graves’ disease, an autoimmune condition, is one of the most common causes of hyperthyroidism. Experts think an underlying mechanism that contributes to autoimmunity may explain why someone develops arthritis and hyperthyroidism.

Additionally, having one disease may worsen the other. A 2020 study suggests that people with RA and thyroid disease report worsened subjective RA symptoms.

Read on to learn more about the link between hyperthyroidism and arthritis, including their causes, treatment options, and when to contact a doctor.

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The thyroid is a butterfly-shaped gland in the neck that is part of the endocrine system. It produces thyroid hormones that help regulate the body’s temperature, energy levels, metabolism, weight, and more.

Hyperthyroidism is a condition that causes the body to produce too much thyroid hormone.

One of the most common causes of hyperthyroidism is Graves’ disease. This is an autoimmune disease that causes the immune system to attack the thyroid, stimulating it to produce too much thyroid hormone.

Researchers have long documented a link between hyperthyroidism and RA.

In one 2018 study, researchers compared 11,782 people who had RA with 57,973 controls. They found that thyroid dysfunction was more common in people with RA. Hypothyroidism, which refers to an underactive thyroid, was present in 16% of people with RA compared with 11.7% of the control group.

Hyperthyroidism was also more common in people with RA. It was present at a rate of 2.33% compared with 1.81% among controls.

Researchers do not fully understand the link between RA and hyperthyroidism. However, the results of the 2018 study show there is a link between RA and various forms of thyroid dysfunction.

There are several potential explanations, including:

  • Autoimmunity: One common cause of hyperthyroidism is the autoimmune condition Graves’ disease. RA is also an autoimmune disease.
  • Underlying syndromes and genetic risk factors: It is possible that the two diseases share underlying risk factors or genetic predispositions. Researchers have already identified one shared risk factor. Polyglandular autoimmune syndromes are a group of genetic diseases that cause endocrine disorders and various autoimmune diseases.
  • Treatment factors: Treating one disease may change the body in a way that increases the risk of developing another condition. For example, some RA drugs may damage the thyroid, increasing the risk of thyroid dysfunction and autoimmune hyperthyroidism.
  • Environmental triggers: While genetics play a role in the development of RA and hyperthyroidism, environmental factors also increase the risk and may change the behavior of genes relating to these diseases. The two diseases may share certain environmental risk factors.
  • Inflammation: Systemic inflammation from one autoimmune disease, such as RA, may increase the risk of another autoimmune disease, including autoimmune hyperthyroidism.

Researchers have not found that hyperthyroidism causes arthritis. However, they have found that there is a higher risk of RA among people with thyroid disease.

A 2020 paper emphasizes that the prevalence of RA is one to three times higher among people with autoimmune thyroid disease. Despite this, the study did not explain the mechanism behind this. Therefore, more research is necessary to identify the precise factors linking RA and thyroid disease.

It is important to note that treating thyroid disease will not prevent RA, but the presence of thyroid disease may indicate someone has a higher risk of RA.

Interestingly, muscle weakness is one of the most common symptoms of autoimmune hyperthyroidism. People may mistake this weakness for a sign of arthritis. This means that a person may have hyperthyroidism but think that they have arthritis.

Though hyperthyroidism and RA sometimes occur together, they are separate medical conditions. A person must treat both individually to achieve symptom relief and reduce the risk of complications.

There is no cure for RA, but several treatments can help manage symptoms. They include:

  • Disease-modifying anti-rheumatic drugs: This large group of drugs reduces inflammation and can prevent further attacks on the joints. In many people, these drugs bring about disease remission.
  • Pain medication: This may include over-the-counter drugs and prescription pain relievers.
  • Physical therapy: Physical therapy can help improve function, reduce pain, and help a person make activity modifications that make daily tasks easier.
  • Lifestyle changes: Some people find that lifestyle changes, such as getting more exercise, reduce the frequency or severity of RA flares.

Treatment for hyperthyroidism focuses on reducing the secretion of thyroid hormone. This may include:

  • Medication: Antithyroid hormone medication can block or reduce thyroid hormone secretion.
  • Radioactive iodine: This treatment prevents the thyroid gland from continuing to overproduce thyroid hormone.
  • Thyroidectomy: This is the surgical removal of the thyroid. With this option, a person will need supplemental thyroid hormone treatment for the rest of their life.

A person may also need treatment for symptoms. For example, beta-blockers can help with high blood pressure and anxiety.

Hyperthyroidism and RA sometimes occur together. A person may also develop other thyroid diseases, such as Hashimoto’s hypothyroidism, along with RA.

While health experts have clearly established a correlation between the conditions, the cause behind this link is not. Researchers continue to look into this connection.

Eventually, they may discover common disease pathways, and this could help with identifying new or different treatments. At present, doctors view the conditions as two separate disorders, and each requires its own treatment.