What is Functional Neurological Disorder (FND)?

FND (Functional Neurological Disorder) is real—meaning the symptoms are not “imaginary”—but the underlying issue isn’t a detectable injury or disease like stroke, MS, or a damaged nerve pathway on the usual scans and exams.

Instead, FND is thought of as a problem with how the brain and nervous system are working together: the networks that control movement, coordination, sensation, and predictions about what will happen can become dysregulated. This can lead to symptoms such as weakness or paralysis, abnormal movements (tremor, jerking, dystonia), gait or balance problems, sensory changes, speech problems, and sometimes blackouts/seizure-like episodes.

A key feature is variability: symptoms can worsen or improve depending on context (fatigue, stress, attention, safety, distraction), and they may shift in form over time.

Treatment focuses on retraining the nervous system and reducing the processes that keep symptoms going—often involving education about the diagnosis, physiotherapy/occupational therapy, psychotherapy (trauma-focused or somatic approaches), and addressing comorbid issues like chronic pain, migraine, anxiety, sleep problems, or dysautonomia.

How is FND diagnosed?

Clinicians diagnose FND not by “ruling out everything” only, but by finding positive signs on history and exam—patterns that are typical of functional symptoms (for example, certain inconsistent weaknesses, movement that changes with distraction, or specific features of functional seizures).

Due to similarities, FND can be misdiagnosed as a neurological disorder, and it can take years for the patient to find out that he, she, or they does not actually have a neurological disorder. FND has been diagnosed in children, teenagers, and adults.

Clinicians often look for four related features: distractibility, suppressibility, variability, and entrainment. They are especially useful for movement symptoms, tremor, weakness, gait problems, and abnormal postures, although “entrainment” applies most directly to rhythmic movements such as tremor.

• Distractibility: The symptom improves, disappears, or changes when attention is directed to another task. For example, weakness may improve during an automatic movement, an abnormal gait may look more normal when walking backward, or a tremor may lessen during mental arithmetic.

• Suppressibility: The symptom can be reduced or temporarily stopped by a deliberate action, change in posture, or different movement. This does not mean the person is consciously producing the symptom. It means the symptom can be modified by voluntary control under certain conditions.

• Variability: The symptom changes more than would typically be expected. This may involve its severity, speed, rhythm, direction, distribution, or triggers. A person may show marked difficulty with one requested movement but perform a similar movement better automatically or in another context.

• Entrainment: A rhythmic symptom—usually a tremor or shaking movement—changes to match the rhythm of a voluntary movement elsewhere in the body. For example, a shaking limb may adopt the tapping rhythm of the opposite hand. This is less relevant to non-rhythmic symptoms such as isolated weakness or sensory changes.

These are positive clinical signs, meaning they help support an FND diagnosis through the way the symptom behaves. They are not proof on their own, and clinicians interpret them alongside the history, neurological examination, and any tests needed to assess other or coexisting conditions. FND symptoms are genuine and involuntary; these terms describe symptom behavior, not conscious fabrication.

FND and the Nervous System

As part of Dr. Moenter’s applied polyvagal approach to working with functional neurological symptoms, she divides symptoms into two categories: those of a nervous system in sympathetic activation (such as functional seizures, twitches, jerks, pain, etc.) and those of a nervous system in dorsal vagal collapse (such as paralysis, drop attacks, limb weakness, etc.).