Functional neurological disorder (FND), or conversion disorder, is a complex condition that causes neurological symptoms, like fainting and tremors, without an apparent structural problem in the nervous system.

According to the Journal of Psychiatry and Neuroscience, FND occurs in 4–12 per 100,000 people. The exact cause is not completely understood, but stress can be a major contributor.

While it can affect children, FND is more common among adolescents and adults. People in rural settings and military personnel may be at higher risk of FND than other groups.

Individuals who have FND experience physical symptoms. These symptoms have no underlying structural cause and are often associated with an emotional or psychological crisis. However, many individuals have FND that did not result from an emotional or psychological cause.

A person with FND has no control over the symptoms they experience and does not consciously or deliberately produce them.

Typical signs and symptoms of FND include:

Symptom duration and severity

Symptoms may come and go, or they may persist. They can vary in severity and location.

In some cases, symptoms resolve within a short period. However, in some people, they may continue for months or years and can hinder a person’s ability to work and carry out everyday activities.

According to FND Hope, a non-profit patient advocacy organization for people with FND, the symptoms of FND can be as debilitating as those of multiple sclerosis or Parkinson’s disease.

The exact cause of FND is not known.

One theory is that FND results from an “internal conflict,” and the symptoms are the body’s attempt to provide a solution to this stress.

For example, someone who believes violence is wrong yet experiences an urge to react violently to a traumatic situation may experience numbness in their arms or legs as a way of suppressing the urge to hit or kick.

However, some people may develop FND in the absence of stress, depression, or other psychological factors.

Some studies have shown that people with FND have decreased functional connectivity in certain parts of their brains, including those parts that control the muscles and senses. This indicates the body’s lack of control over physical movement or actions.

Factors that may increase the risk of developing FND include:

Diagnosing FND may take a long time, as the symptoms do not result from an underlying physical condition and can mimic the symptoms of many other conditions. Doctors should not diagnose FND on the basis that tests for other conditions have proved negative.

In many cases, both a neurologist and a psychiatrist will be involved in a diagnosis. A neurologist will help rule out underlying neurological conditions, while a psychiatrist can rule out other psychological causes and confirm a diagnosis of FND.

Although there is no standard test to check for FND, tests commonly used for diagnosis include:

A health assessment and physical exam

A doctor will note any symptoms a person is experiencing and ask about life changes, traumas, and major stressors. They may also take a full medical history and family history.

A doctor may carry out functional tests to check a person’s reflexes, balance, and physical movements.

Imaging tests

X-rays and MRI scans can identify whether symptoms are related to brain injuries or neurological abnormalities.

Electroencephalogram scans can track brain waves, allowing doctors to detect problems associated with the brain’s electrical activity, such as epilepsy.

DSM criteria

A psychiatrist will use the diagnostic criteria laid out in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) to make a diagnosis.

To receive a diagnosis of FND, people will:

  • have one or more symptoms that affect their movement or senses and are outside of their conscious control
  • not be able to attribute their symptoms to drug use or a physical or neurological condition
  • find that their symptoms cause significant distress or problems socializing, at work, or in other areas of life, or are significant enough that medical evaluation is required

Due to the symptoms of FND, there is the potential for doctors to misdiagnose the condition.

A 2005 review suggests that the misdiagnosis rate for FND has averaged at approximately 4% since 1970. Another report indicates that 41% of people with rare diseases receive an incorrect diagnosis at least once.

Common misdiagnoses for people with FND include:

Symptoms can resolve without treatment in some people with FND, particularly after they receive assurance that their symptoms are not related to a more serious health condition.

However, treatments may be beneficial for those with:

  • co-occurring psychological conditions
  • severe FND symptoms
  • symptoms that are slow to resolve
  • recurrent symptoms

In general, doctors recommend a combination of treatments. These treatments include:

  • Psychotherapy: People with FND related to a stressful or traumatic event or an underlying mental health condition may benefit from working with a psychotherapist or psychologist. Some individuals with FND undergo cognitive behavioral therapy.
  • Physical therapy: People may treat the physical symptoms of FND, such as impaired movement or muscle weakness, or pain, with physical therapy.
  • Medication: Antianxiety drugs or antidepressants may help treat the stress or anxiety that contributed to the onset of FND.
  • Transcranial magnetic stimulation (TMS): This treatment uses magnetic fields to stimulate certain parts of the brain. Some reports suggest TMS is beneficial for people with FND, but there is limited evidence at this stage.
  • Lifestyle changes: Engaging in activities that alleviate stress and anxiety, such as yoga, meditation, and progressive muscle relaxation, may be helpful for some people with FND. Eating a balanced diet, getting enough sleep, fostering positive relationships, and maintaining a good quality of life also contribute to stress reduction.

The duration and severity of symptoms vary from person to person. Typically, the symptoms are not life threatening, but complications that arise may be debilitating or decrease a person’s quality of life.

Once reassured that their symptoms are not related to a physical condition or serious illness, many people with FND recover.

However, some people may experience ongoing symptoms, recurring symptoms, or the development of new symptoms at a later stage, particularly if:

  • they delay treatment
  • symptoms develop slowly
  • symptoms do not improve quickly
  • symptoms are not stress-related
  • symptoms include tremors or seizures
  • there are co-occurring psychological conditions

It is important to consult a doctor if a person experiences any of the signs and symptoms of FND, particularly as symptoms can be associated with other medical conditions. In these situations, early intervention may be important to resolve the underlying problem.

Early intervention is also important as untreated FND may result in further complications or debilitation.