Multiple sclerosis (MS), hypothyroidism, and hyperthyroidism may share a link that makes it more likely that a person will develop hypothyroidism or hyperthyroidism if they have MS.

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MS is a chronic autoimmune condition that involves the immune system attacking the healthy cells of the central nervous system. This damage can cause different symptoms in different people.

The two most common thyroid conditions are hypothyroidism and hyperthyroidism. Hypothyroidism occurs when the thyroid does not produce enough thyroid hormone for the body. Hyperthyroidism occurs when the thyroid produces too much thyroid hormone.

The most common cause of hypothyroidism is an autoimmune condition called Hashimoto’s disease. Graves’ disease, which is also an autoimmune condition, is the most common cause of hyperthyroidism.

Although these are separate conditions, they may share a link that makes it more likely that a person will develop a thyroid condition if they have MS.

The following sections explain what scientists currently know about this possible connection.

MS affects about 1 million people in the United States alone. However, doctors and researchers still do not fully understand the exact cause of MS.

According to the National Multiple Sclerosis Society, a combination of factors may cause MS. Some factors that may lead to this condition include:

  • immune system disorders
  • environmental factors
  • infections
  • genetics

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Hashimoto’s disease is the most common cause of hypothyroidism.

For many years, research has shown a possible connection between MS and thyroid disorders. In an older study from 1999, for example, researchers found that women with MS were three times more likely to develop hypothyroidism than women without MS.

In a study from 2005, researchers found significant evidence to suggest a link between MS and thyroid issues. However, the researchers did not believe that having one necessarily meant that a person would get the other. They also stated that this link is still unproven.

This study also found a significant co-occurrence between MS and Graves’ disease.

In a 2018 study, researchers learned more about the connection between MS and Hashimoto’s disease. They found that both conditions share a common deregulation of anti-inflammatory mechanisms in the body. In other words, both conditions involve inflammation.

However, the study also noted that additional research is necessary to fully understand the relationship between MS and Hashimoto’s disease.

Treatment concerns

It is possible that certain treatments for MS may trigger thyroid issues.

In a 2009 study, researchers found that interferon therapies may be responsible for thyroid issues such as thyroid nodules and subclinical hypothyroidism. They recommended that doctors monitor people with MS for thyroid issues.

In a 2017 study involving 69 people with MS who were receiving treatment with alemtuzumab infusions, 20% developed thyroid disease within 18 months of their initial treatment. Of those who developed thyroid disease, 50% developed hyperthyroidism.

However, the researchers also found that thyroid disease spontaneously resolved or remained subclinical in roughly a third of these people.

As a result, the study authors recommended ongoing active monitoring of people receiving treatment with alemtuzumab infusions for the first 5 years.

If a person has any concerns about the impact of their MS treatments on their thyroid, or if they are concerned about any other potential side effects, they should talk with a doctor to learn more about other available treatment options.

MS and the thyroid are not fully connected. However, based on some research, it is possible that having one condition may make developing the other condition more likely.

The Multiple Sclerosis Foundation states that MS and autoimmune hypothyroidism frequently occur together. That said, it also notes that other autoimmune conditions — including type 1 diabetes, rheumatoid arthritis, and psoriasis — may occur more frequently than hypothyroidism with MS.

It recommends that doctors screen for thyroid issues in all people with MS.

Hypothyroidism

Hypothyroidism develops when the thyroid does not produce enough thyroid hormone for the body.

According to the NIDDK, thyroid hormone is involved in several organs and tissues throughout the body. If those organs do not get enough of the hormone, they will not perform as well as they should.

Hypothyroidism causes some symptoms that are similar to those of MS. According to the NIDDK, some symptoms of the condition include:

  • joint and muscle pain
  • difficulty handling cold temperatures
  • fatigue
  • depression
  • a slowed heart rate
  • constipation
  • weight gain
  • fertility issues

The National Multiple Sclerosis Society states that some symptoms of MS that are similar to those of hypothyroidism include:

  • depression
  • fatigue
  • constipation or other bowel issues
  • weakness
  • sexual issues

Although some research has suggested a possible link, having one condition does not mean that a person will automatically get the other.

Hyperthyroidism

According to the NIDDK, hyperthyroidism most often develops due to an autoimmune condition known as Graves’ disease. This condition causes the immune system to attack the thyroid and make more thyroid hormone than the body needs.

Nearly every organ in the body uses thyroid hormone, so hyperthyroidism can cause serious problems with the heart, the bones, the muscles, the menstrual cycle, and fertility. It can also affect the skin and eyes.

Some symptoms of hyperthyroidism include:

  • a fast and irregular heartbeat
  • frequent bowel movements or diarrhea
  • an enlarged thyroid, or goiter
  • heat intolerance
  • nervousness or irritability
  • tiredness or muscle weakness
  • trembling hands
  • difficulty sleeping
  • weight loss

According to the National Multiple Sclerosis Society, fatigue, muscle weakness, bowel issues, and tremors are also symptoms of MS.

Shared risk factors

MS and thyroid conditions may also share some common risk factors.

Some research has suggested that the cause of MS is likely a combination of genetic predisposition and infectious agents that trigger an immune response.

It notes that some risk factors include smoking, obesity, and low exposure to the sun. However, these factors are not useful for predicting a person’s likelihood of developing MS.

The NIDDK states that there are several risk factors for hypothyroidism. Some common ones include:

  • family history
  • recent radiation treatment
  • having type 1 diabetes or rheumatoid arthritis

According to the NIDDK, a person’s risk of developing Graves’ disease increases if other family members have the condition. Hyperthyroidism may develop from a combination of genes and an outside trigger, such as a virus.

Some research has also shown that shared risk factors between MS and thyroid issues include genetic susceptibility and environmental exposures. In other words, a person with certain genetic susceptibility or environmental exposure may be at increased risk of developing both MS and a thyroid condition.

However, the researchers stated that more investigations are necessary to fully understand the risk factors.

MS and thyroid conditions share some similar potential causes and symptoms. However, they are not directly related.

People with MS or either hypothyroidism or hyperthyroidism may or may not develop the other condition.

A person with MS should talk with a doctor about screening for thyroid issues. They may develop thyroid issues due to having similar risk factors or as a result of using certain MS medications.