The cause of functional neurological symptom disorder is not known.
According to the National Organization for Rare Disorders, functional neurological symptom disorder (FND) is thought to occur in 14-22 cases per 100,000 people.
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, however, have no underlying physical cause and are often associated with an emotional or psychological crisis.
A person with FND has no control over the symptoms they experience and do not consciously or deliberately produce them.
Typical signs and symptoms of FND include:
- deafness or hearing difficulties
- difficulty concentrating
- difficulty swallowing
- impaired movement
- lack of responsiveness
- loss of balance
- loss of the senses, such as smell or touch
- memory problems
- pain in the muscles, skin, or joints
- speech problems
- tingling sensations in the skin
- vision problems
Symptom duration and severity
Symptoms may come and go, or they may persist, and they can vary in their severity and location.
In most cases, symptoms resolve in a short time-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.
Causes and risk factors
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 even in the absence of stress or depression.
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:
- dissociative disorders
- personality disorders
- distressing life events
- childhood traumas
- having a family member with FND
A psychiatrist may work in conjunction with a neurologist to diagnose FND.
Diagnosing FND may take a long time, as the symptoms are not caused by an underlying physical condition and can mimic the symptoms of many other disorders. 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, the tests commonly used for diagnosis include:
A health assessment and physical exam
A doctor will note any symptoms a person is experiencing and will ask about life changes, traumas, and major stressors. The doctor may also take a full medical history and family history.
A doctor may also carry out functional tests to check for normal reflexes, balance issues, and physical movements.
X-rays and MRI scans can identify whether symptoms are related to brain injuries or neurological abnormalities.
EEG (electroencephalogram) scans can track brain waves, allowing doctors to detect problems associated with the brain's electrical activity, such as epilepsy.
A psychiatrist will use the diagnostic criteria laid out in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-5) to make a diagnosis.
To be diagnosed with FND, people:
- must have one or more symptoms that affect their movement or senses and are outside of their conscious control
- must not be able to attribute their symptoms to drug use or a physical or neurological condition
- may attribute their symptoms to a traumatic or stressful event (although this does not always have to be the case)
Due to the symptoms of FND, there is the potential for the condition to be misdiagnosed.
A 2005 review suggests that the misdiagnosis rate for FND has averaged at approximately 5 percent since 1970. Another report indicates that 41 percent of people with rare diseases will be misdiagnosed at least once.
Common misdiagnoses include:
- Guillain-Barre syndrome: A rare autoimmune disorder characterized by muscle weakness and pain.
- HIV or AIDS.
- Health anxiety: A psychological disorder characterized by excessive thoughts about having an undiagnosed illness.
- Lupus: An autoimmune disease with symptoms including fatigue and joint pain.
- Myasthenia gravis: A muscle weakness disorder.
- Neurological disorders: Disorders which affect the central nervous system, such as epilepsy, multiple sclerosis, polyneuropathy, and Parkinson's disease.
- Spinal cord injury.
Physical therapy may help to treat the physical symptoms of FND.
Symptoms can resolve without treatment in some people with FND, particularly after they are assured that their symptoms are not related to a more serious health condition.
However, treatments may be beneficial for those with:
- other (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 behavior therapy (CBT).
- Physical therapy. The physical symptoms of FND, such as impaired movement or muscle weakness or pain, may be treated with physical therapy.
- Medication. Anti-anxiety drugs or antidepressants may help to 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:
- treatment is delayed
- symptoms develop slowly
- symptoms do not improve quickly
- symptoms are not stress related
- symptoms include tremors or seizures
- there are co-occurring psychological conditions
When to see a doctor
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.