Fibromyalgia and Ankylosing Spondylitis

Reviewed by: HU Medical Review Board | Last reviewed: February 2019 | Last updated: August 2021

Fibromyalgia is a condition that causes widespread pain in the body. People with ankylosing spondylitis (AS) have a greater risk of developing fibromyalgia, which can complicate their symptoms and the progression of their AS.

What is fibromyalgia?

Fibromyalgia is a neurological condition. Researchers believe that the condition affects the nerves by making them more sensitive to pain. While experts don't know why fibromyalgia occurs, it can begin after a physical trauma, infection, or significant emotional stress.1 In the general population, fibromyalgia is more common in women than men, although some studies have found there is not a difference in gender among people with AS, with both men and women with AS getting fibromyalgia at similar rates.1,2 Fibromyalgia is common in people with other painful conditions, including irritable bowel syndrome, migraine, irritable or overactive bladder, depression or anxiety, and temporomandibular joint (TMJ) disorders.1,3

How common is fibromyalgia among people with AS?

Fibromyalgia occurs in approximately 2-4 percent of the general population.3 In people with AS, fibromyalgia is more common. One meta-analysis (a research study that reviews and combines data from several studies) found that the prevalence of AS varied among the studies, from 4 percent to 25 percent.4 Another recent study found that the prevalence of fibromyalgia may be as high as 43 percent in people with AS.2 Despite this wide variation, fibromyalgia is significantly higher among people with AS than those without the condition.

What are the symptoms of fibromyalgia?

Fibromyalgia causes widespread, chronic pain in the muscles, joints, and/or skin. The pain is often described as a dull ache and points may be tender to the touch. Fibromyalgia also causes significant fatigue, sleep problems, and cognitive difficulties (challenges with concentration or thinking clearly, sometimes called "fibro fog").1,3

How does fibromyalgia complicate AS?

Because both fibromyalgia and AS can cause similar symptoms, there is a risk of misdiagnosis. Some people may be diagnosed with fibromyalgia and AS may be missed. While a proper diagnosis of both conditions is important, fibromyalgia does not cause damage to the structure of the body like AS can. Receiving a diagnosis and getting treated for AS is important to slow or stop the disease progression.2,5

Fibromyalgia can also complicate AS by increasing the disease activity of AS, causing worsening symptoms. However, fibromyalgia may only increase the experience of symptoms, such as pain and fatigue. There have been conflicting studies on whether fibromyalgia increases inflammatory markers (like C-reactive protein, CRP) or other physical findings in people with AS.6,7

How is fibromyalgia diagnosed?

Fibromyalgia is diagnosed with a physical exam and medical history. Generally, a diagnosis of fibromyalgia may be made if the individual has experienced pain both above and below the waist for more than three months and there is no underlying condition that causes the pain. While there are no blood tests that diagnose fibromyalgia, doctors may order blood tests to rule out other conditions.1

How is fibromyalgia treated?

Although there is no currently no cure for fibromyalgia, symptoms can be treated and are often managed with a combination of approaches, including over-the-counter and prescription medications, physical therapy, exercise, counseling, stress management techniques, and complementary approaches, like acupuncture.1,3

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