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.
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Symptoms
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
- fatigue
- impaired movement
- lack of responsiveness
- loss of balance
- loss of the senses, such as smell or touch
- memory problems
- numbness
- pain in the muscles, skin, or joints
- paralysis
- seizures
- speech problems
- tingling sensations in the skin
- tremors
- twitches
- vision problems
- weakness
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.
According to FND Hope, a non-profit patient advocacy organization for people with FND, symptoms of FND can be as debilitating as multiple sclerosis (MS) or Parkinson's disease.
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
Diagnosis
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.