People with ankylosing spondylitis are more likely than other people to receive a diagnosis of an autoimmune thyroid condition, such as Hashimoto’s disease.

Hashimoto’s disease, also known as Hashimoto’s thyroiditis, and ankylosing spondylitis are both autoimmune conditions. This classification means that they develop when the immune system attacks the body’s own tissues.

In Hashimoto’s disease, the immune system attacks and damages the thyroid gland, which can lead to hypothyroidism, or an underactive thyroid. Hypothyroidism can cause fatigue and weight gain, among many other symptoms.

In ankylosing spondylitis, the immune system attacks the joints and ligaments in the spine. Common symptoms include back pain and stiffness. The condition may also cause inflammation in other joints and organs, such as the eyes.

Some small studies have found an association between Hashimoto’s disease and ankylosing spondylitis. People who have one of these conditions may have an increased risk of developing the other condition, as well.

A 2012 study evaluated the thyroid health of 108 people with ankylosing spondylitis. The authors concluded that people with ankylosing spondylitis have an increased likelihood of having autoimmune thyroid disease.

A 2014 study evaluated Hashimoto’s disease more specifically. The researchers compared the thyroid health of 80 people with ankylosing spondylitis with that of 80 people without the condition. Roughly 10% of those with ankylosing spondylitis met the criteria for Hashimoto’s disease. In comparison, only 2.5% of those without ankylosing spondylitis had Hashimoto’s disease.

More research is necessary to confirm the potential link between Hashimoto’s disease and ankylosing spondylitis. Experts do not know the exact cause of either disease, but they believe that a combination of genetic and environmental factors likely plays a role.

More research is necessary to determine whether ankylosing spondylitis directly contributes to thyroid problems, including Hashimoto’s disease. Shared genetic or environmental risk factors may account for the link between these two conditions.

Certain immune cells and processes appear to play a role in both diseases. These include tumor necrosis factor (TNF), a small protein that the immune system uses for cell signaling, which drives inflammation.

Some research suggests that in people with ankylosing spondylitis, anti-TNF treatments may help prevent autoimmune thyroid disease. Anti-TNFs are a class of biologic medications that help reduce inflammation in people with certain autoimmune conditions, including ankylosing spondylitis.

For instance, in the abovementioned 2012 study, people with ankylosing spondylitis were less likely to have autoimmune thyroid disease if they were receiving treatment with anti-TNFs.

A 2020 study also found that thyroid dysfunction was less common in people with ankylosing spondylitis who were receiving anti-TNF treatment compared with those who were taking nonsteroidal anti-inflammatory drugs (NSAIDs).

Hashimoto’s disease is not a connective tissue disease. However, it can cause muscle pain, joint pain, and other symptoms similar to those of certain connective tissue disorders.

People with Hashimoto’s disease show signs of connective tissue diseases more often than the average person. These conditions include:

  • rheumatoid arthritis
  • psoriatic arthritis
  • ankylosing spondylitis
  • Sjögren’s disease

The researchers behind a study in Clinical Rheumatology note that people with Hashimoto’s disease also have an increased risk of fibromyalgia. This chronic pain condition causes muscle and joint pain, tender points, and other symptoms.

For people with Hashimoto’s disease or ankylosing spondylitis, attending regular checkups with a doctor is important. These individuals should let a doctor know if they experience any changes in their health, even if those changes seem unrelated to their condition.

Autoimmune conditions such as Hashimoto’s disease and ankylosing spondylitis can affect multiple parts of the body. People with one autoimmune condition have an increased risk of developing another.

A person’s doctor may order tests to determine the cause of their symptoms. The doctor may then recommend changes to the person’s treatment plan, including their prescribed medication.

Treating ankylosing spondylitis may involve NSAIDs, biologics such as anti-TNFs, or other medications. To treat hypothyroidism from Hashimoto’s disease, doctors may prescribe the medication levothyroxine.

A person’s doctor may also recommend lifestyle changes to help manage the symptoms, reduce the risk of complications, and improve quality of life.