The Connection Between Fibromyalgia and Thyroid Disease

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Thyroid disease and fibromyalgia are connected in a number of important ways. Not only do these conditions share many common symptoms, but both are often misdiagnosed. Even when properly diagnosed, it's important to be aware of how people with one of these conditions may be predisposed to the other, and how having a combination of both conditions impacts each disease. Despite the connections, however, theories looking into a possible underlying cause of both conditions span the spectrum from autoimmunity, to dysfunction of the hypothalamus, to viral and bacterial infections, and more. Let's look at information to date on the connection between autoimmune thyroid disease and fibromyalgia, and share some thoughts on what you should know today if you are coping with either or both of these conditions.

Thyroid Disease and Fibromyalgia Basics

A connection between thyroid disease and fibromyalgia begins with similarities in the incidence and populations affected by these diseases.

Incidence

Both thyroid disease and fibromyalgia are very common in the United States. Estimates suggest that at least 5 percent of adults in the United States are living with hypothyroidism, though this number does not include the roughly 13 million people thought to have undiagnosed hypothyroidism. Autoimmune hypothyroidism or Hashimoto's disease is the most common form of hypothyroidism. According to the CDC, 2 percent of the population, or around 4 million people, are living with fibromyalgia.

Combined Occurrence

Not only are hypothyroidism and fibromyalgia both common, but they frequently occur together. According to a 2017 study, the prevalence of fibromyalgia in the general population was 2 percent to 7 percent, but as high as 30 percent to 40 percent in people. Using newer diagnostic criteria for fibromyalgia, the incidence rose to 62 percent.

Among people with hypothyroidism, fibromyalgia was more common in those who were overweight, had positive anti-thyroperoxidase antibodies, and who had been living with thyroid disease for a long period of time.

Similarities in Epidemiology

Thyroid disease and fibromyalgia tend to affect a similar population of people:

  • Gender: Both conditions are much more common in women
  • Age: Both conditions are most common during the childbearing years and in middle age (though they can occur at any age)

Similarities such as these raise the question as to whether both conditions may occur due to an underlying issue that predisposes people to both diseases.

Shared Symptoms

There are a number of symptoms that are similar between hypothyroidism and fibromyalgia as well as some that are more common with one condition than the other.

Overlapping Symptoms

Symptoms that are very common among both people with hypothyroidism and those with fibromyalgia include:

  • Fatigue and exhaustion, with non-restful sleep
  • Body aches (muscle and joint pain)
  • Cognitive problems, often referred to as "brain fog"
  • Depression and anxiety

Symptoms That are More Common in Hypothyroidism

In comparison to fibromyalgia, people with hypothyroidism are more likely to experience weight gain, thinning of hair, constipation, dry skin, and menstrual irregularities.

Symptoms That are More Common in Fibromyalgia

Symptoms that are more common with fibromyalgia than with hypothyroidism include headaches, paresthesias (abnormal sensations such as tingling of the extremities), and muscle spasms. In addition, cognitive concerns and depression are often more pronounced with fibromyalgia.

Symptoms of Thyroid Disease Can Affect Fibromyalgia and Vice Versa

Autoimmune thyroid disease often leads to a worsening of fibromyalgia symptoms. Fibromyalgia may also enhance the symptoms of thyroid disease, or make it more difficult to know if thyroid hormone replacement therapy is optimal.

Potential Causes

Hashimoto's disease (the most common form of hypothyroidism) is an autoimmune disease, in which autoantibodies (antibodies against self) damage thyroid tissue. There is a great deal of controversy over the underlying cause of fibromyalgia. Some researchers believe that fibromyalgia may also be an autoimmune disease, while others believe that symptoms thought to be fibromyalgia may actually be symptoms related to hypothyroidism instead. Yet others have postulated that both autoimmune thyroid disease and fibromyalgia are caused by a similar underlying process that can predispose to both conditions. Whatever the connection, the two conditions are often connected.

Looking upstream for potential causes of both conditions, some of the possibilities that have been suggested include:

Autoimmunity

The autoimmune basis of Hashimoto's disease can be demonstrated with the presence of anti-thyroperoxidase (TPO) antibodies. A 2017 study found a potential link to autoimmune disease with fibromyalgia as well. Compared to the general population, people with fibromyalgia had a high degree of positivity to TPO antibodies as well. Theories vary, though some have theorized that underlying autoimmune disease precipitates the development of both conditions.

Suppression of the Hypothalamus

The hypothalamus is a region of the brain that has been likened to the utility center. It functions to maintain homeostasis, or a steady state in the body by regulating hormone levels (including thyroid hormones), sleep, temperature, hunger, and the autonomic nervous system (the involuntary part of the nervous system that controls blood pressure, blood flow, digestion, and much more).

Some researchers have suggested that dysfunction of the hypothalamus may be the root cause of both disorders, and by itself, hypothalamic dysfunction can cause many of the symptoms attributed to thyroid disease or fibromyalgia. Suppression of the hypothalamus may occur due to problems with the mitochondria in hypothalamic cells, the organelles that are considered the "energy furnaces" of cells.

Viral or Bacterial Infections

Both autoimmune disease and fibromyalgia sometimes occur following an infection with the Epstein Barr virus (the cause of mononucleosis), or Lyme disease. Epstein Barr virus infections, in particular, have been implicated in autoimmune diseases when a component of the virus resembles proteins in the body (so that antibodies are "accidentally" produced against self), or due to the immune system being "overactivated" in response to the infection.

Trauma

As with some infections, both autoimmune thyroid disease and fibromyalgia are sometimes preceded by trauma. Trauma, in turn, lends credence to an autoimmune basis, as it activates the immune system. This activation might lead to a hyperactive state (causing autoimmunity) after the injury has resolved.

Hormonal Problems

Other hormonal problems, such as low cortisol production by the adrenal gland, have also been postulated as underlying causes of both conditions.

Diagnosis

Hypothyroidism and fibromyalgia have an unfortunate commonality in that they are both frequently misdiagnosed.

The diagnosis of hypothyroidism often begins with a TSH test, though some experts believe that a normal TSH is insufficient to rule out thyroid disease, especially in those who have a family history of an autoimmune thyroid condition (such as Hashimoto's thyroiditis or Grave's disease). In this case, diagnostic tests may include a total and free T4, a total and free T3, and thyroid antibody tests. In addition, people with thyroid disease who have thyroid autoantibodies are also more likely to have fibromyalgia. Thyroid testing is extremely important as hypothyroidism is underdiagnosed, and frequently misdiagnosed as premenstrual syndrome, depression (including postpartum depression), stress, and more.

The diagnosis of fibromyalgia is primarily a clinical diagnosis based on symptoms of pain, fatigue, and cognitive symptoms. Since under-treated hypothyroidism can cause symptoms that are very similar, it can be challenging to know whether a person meets the criteria for fibromyalgia with hypothyroidism.

Separating Out the Diagnoses

Before diagnosing fibromyalgia, thyroid function testing should be done. If autoimmune hypothyroidism is found, it's reasonable to treat the thyroid condition alone at first and see if pain resolves. If a person is already on thyroid replacement therapy and has symptoms of fibromyalgia, the goal should be optimal control before the diagnosis is made (see below).

Differential Diagnosis

In addition to fibromyalgia and hypothyroidism, there are other conditions that may cause similar symptoms (and can make these diagnoses less obvious and challenging, or mask the development of fibromyalgia with hypothyroidism and vice versa). These include:

  • Anemia
  • Depression and/or anxiety
  • Vitamin D deficiency
  • Kidney disease
  • Liver disease
  • Infections (such as mononucleosis, Lyme disease, and more)
  • Sleep apnea
  • Hormonal conditions (such as menopause or premenstrual syndrome)
  • Other autoimmune diseases (such as lupus)

Tips for Those Living with Either Condition

The connection between hypothyroidism and fibromyalgia is more than academic, and an awareness of this overlap may be important whether you have one of these conditions alone, or a combination of both.

People with Fibromyalgia

If you have fibromyalgia, ask your doctor to test for a thyroid condition that could be contributing to—or even causing your symptoms. This is especially important if you have fibromyalgia that is not responding to treatment. Those who have fibromyalgia may have a predisposition to developing Hashimoto's disease, and autoimmune thyroid disease can worsen the symptoms of fibromyalgia.

People with Hypothyroidism

If you have autoimmune thyroid disease, be aware that you may have a predisposition to developing fibromyalgia. This can be challenging to diagnose, however, since undertreated hypothyroidism can mimic the symptoms of fibromyalgia. Hence, fibromyalgia should not be diagnosed until a person has a normal TSH (though there is controversy about what an "ideal" TSH should be). That said, a normal TSH alone may not be adequate.

"Cellular Hypothyroidism"

Some researchers believe that even if TSH is within normal limits, it doesn't tell whether or not a person has adequate T3 circulating in their bloodstream. In the body, T4 is converted to T3, which is the active form of the hormone at a cellular level. The theory is that a lack of T3 (due to an impairment in the conversion of T4 to T3 in the body) may be insufficient to maintain normal metabolism in cells. We do know that some signs of hypothyroidism, such as an elevated cholesterol level, may persist despite a normal TSH (but become lower when TSH is suppressed), giving indirect support to this theory.

Proponents of this theory claim that levothyroxine alone is not enough to raise circulating T3 levels, and treatments such as combination T4/T3 therapy or natural desiccated thyroid therapy should be considered.

People With Both

While living with both thyroid disease and fibromyalgia is common, make sure to talk to your doctor about optimal thyroid hormone replacement as for people with hypothyroidism alone. Adequate treatment of undertreated hypothyroidism may resolve the symptoms of fibromyalgia.

A Word From Verywell

Thyroid disease and fibromyalgia have many commonalities, though the exact connection between the two conditions is still unclear. What is better understood, however, is that it's important to be aware of both conditions and potential interactions when making a diagnosis and selecting treatment options.

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