Functional disorders: IBS, fibromyalgia, FND and chronic pain

"Functional" is a word doctors use for symptoms that come from a change in how part of the body works, rather than from damage to its structure. Irritable bowel syndrome (IBS), fibromyalgia, functional neurological disorder (FND) and chronic primary pain are some of the best-known examples.

These conditions are real, common and often disabling. Standard tests and scans are often normal, but doctors can recognize them by their typical patterns. They are not imagined, and they are not a sign of weakness. Functional symptoms come up in about a third of visits to family doctors and specialists.¹

What does "functional" mean?

The National Institute of Neurological Disorders and Stroke describes FND as a condition caused by changes in how brain networks work, rather than changes in the structure of the brain. The symptoms are real, even though scans of the brain's structure look normal.²

Some doctors explain this with a computer comparison. The hardware, meaning the body's organs, nerves and tissues, is not broken. The problem is in the software, meaning the way signals are sent, received and processed. Software problems are real problems, and they can sometimes be improved with retraining.

The comparison is useful, but it has limits:

• "Software" does not mean imaginary, made up or under your control.
• It does not mean the cause is purely psychological. Researchers think these conditions involve body systems, such as the immune system, the automatic nervous system and stress hormones. They also involve the brain, such as how body signals are processed and how sensitive the pain system is.¹
• A group of leading researchers describes functional disorders as neither purely physical nor purely mental, but a mix of both.¹

A functional diagnosis should be made from positive signs and typical patterns, not only because tests were normal. As with any diagnosis, doctors also consider other possible causes first.¹ In FND, for example, a doctor may use a bedside test called Hoover's sign to show a typical pattern of leg weakness.²

Common functional disorders

Irritable bowel syndrome (IBS)

IBS causes belly pain along with diarrhea, constipation or both. About 12 in 100 people in the U.S. have it. Women are up to twice as likely as men to have it, and it is more common before age 50.⁴

Experts describe IBS as a problem with brain–gut interaction. In some people, food moves through the gut too fast or too slowly. Others feel pain from normal amounts of gas or stool.⁵ Things linked with a higher risk include a family member with IBS, stressful or hard events in childhood, and a severe gut infection.⁴ People with IBS often also have fibromyalgia, chronic fatigue, chronic pelvic pain, anxiety, depression or somatic symptom disorder.⁴

Weight loss you cannot explain or blood in your stool needs a medical check. See Getting checked.

Fibromyalgia

Fibromyalgia is a long-lasting condition that causes widespread pain and tenderness, often described as aching, burning or throbbing, along with tiredness and poor sleep. Many people also have stiffness, numbness or tingling, and trouble with memory and concentration, sometimes called "fibro fog." Some are more sensitive to light, noise, smells and temperature.⁶

It is more common in women and usually begins in middle age. Brain imaging studies show changes in the nerve pathways that process pain, which helps explain why people with fibromyalgia feel pain more strongly.⁶ U.K. guidelines and the World Health Organization's disease list (ICD-11) count fibromyalgia as a type of chronic primary pain.⁷

Functional neurological disorder (FND)

FND can cause seizure-like episodes, tremor, jerks, unusual postures, weakness or paralysis of a limb, trouble walking, speech problems, dizziness, vision or hearing problems, numbness, pain and extreme tiredness. The symptoms are not produced on purpose. They may get worse when the person pays attention to them and ease when they are distracted.²

FND is one of the most common reasons people are referred to a neurologist, making up about 1 in 6 new referrals.³ Stress and childhood adversity raise the risk, but in most studies more than half of people with FND reported neither.³ Some health workers wrongly assume people with FND are faking, which adds stigma.^2,3 Early diagnosis and treatment can help.²

Functional dizziness is a related condition, often called persistent postural-perceptual dizziness (PPPD). It often follows an inner ear problem or another bout of dizziness. In specialist dizziness clinics, it is the most common cause of long-lasting dizziness. The typical patient is in their mid-50s, and women are affected about twice as often as men.³

Chronic primary pain

Chronic pain means pain that lasts or keeps coming back for more than 3 months. U.K. guidelines describe chronic primary pain as pain with no clear underlying condition, or pain whose impact is out of proportion to any injury or disease that can be seen. It often comes with marked distress and disability.⁷

It includes fibromyalgia, some long-term headaches and face pain, chronic belly or pelvic pain, and chronic muscle and joint pain. It can exist alongside pain from a known cause such as arthritis.⁷ See Chronic pain and mood and Pain in midlife.

ME/CFS: a separate illness

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) shares some symptoms with the conditions above, such as tiredness, pain, poor sleep and dizziness. But it is a distinct illness, and it is important not to confuse the two.

• The CDC describes ME/CFS as a serious, often long-lasting biological illness that affects many parts of the body. Up to 3.3 million people in the U.S. may have it, and more than 9 in 10 have not been diagnosed.⁸
• Its hallmark is post-exertional malaise: symptoms get worse after physical or mental activity. About 1 in 4 people with ME/CFS are confined to bed at some point.⁸
• A 2015 report from the National Academies stressed that ME/CFS is a medical, not a psychiatric or psychological, illness. It noted that patients often reported hostility from health workers and treatments that made their symptoms worse.⁹
• U.K. guidelines advise against graded exercise therapy, which raises activity by fixed steps, for ME/CFS. They say CBT should be offered only to help people cope with a long-term illness, not as a cure.¹⁰

There is no single test for ME/CFS. It is diagnosed through a careful history, a physical exam and targeted tests to rule out other illnesses.^8,9 If you have severe tiredness that worsens after activity, ask your doctor about ME/CFS, and see our self-help page for how its approach to activity differs.

How functional disorders overlap with anxiety and depression

Functional disorders often go along with anxiety and depression.^1,4 The reasons are not fully known. Living with pain, bowel problems or seizures is stressful. Stress, in turn, can make symptoms flare. Some of the same body and brain processes may be involved in both.¹

Overlap does not mean the symptoms are "caused by" anxiety or depression. Experts say psychological features are not required for the diagnosis.¹ In FND, more than half of people in most studies reported no major stress or childhood adversity.³ There is also overlap among the functional disorders themselves. Many people meet the criteria for more than one, such as IBS and fibromyalgia.¹ When anxiety or depression is present, treating it is part of good care and can make the body symptoms easier to live with. See How stress, anxiety and depression cause real body symptoms.

What helps

Guidelines say care should start with a clear diagnosis and a plain explanation of what is happening in the body.^11,12 Many people use a mix of approaches. The badges show how strong the research is (see how we rate evidence).

What usually does not help. For chronic primary pain, U.K. guidelines advise doctors not to start opioids, anti-seizure medicines such as gabapentin, benzodiazepines, anti-inflammatory painkillers or acetaminophen, because evidence of benefit is lacking.⁷ European fibromyalgia guidelines advise against strong opioids.¹¹ If you already take one of these, do not stop on your own. Talk with your doctor about a safe plan.

Common questions

My tests are normal. Does that mean it is psychological?

No. Normal tests mean structural damage has not been found. Functional disorders involve real changes in how the body and nervous system work, and they are diagnosed by their own typical signs.^1,2

Is ME/CFS a functional disorder?

ME/CFS is recognized as its own medical illness, with post-exertional malaise as its key feature. Leading U.S. bodies describe it as biological and medical, not psychological.^8,9

Can functional disorders get better?

Yes. For some people, symptoms are short-lived. For others, they last for years or come and go. Early diagnosis and treatment can lessen symptoms.²

When to get help

See a doctor if you have long-lasting pain, bowel problems, dizziness, weakness, shaking or episodes of passing out, especially if they are new or changing. Get help right away for any warning signs listed on our Getting checked page. Sudden weakness, numbness or trouble speaking needs 911.

Living with a long-term condition can be exhausting. If you feel hopeless or have thoughts of suicide, call or text 988 any time.

Education only. This page is general information written from the sources listed. It is not medical, legal or financial advice and does not replace a doctor, therapist or lawyer who knows your situation. How we write and check pages.