Functional tremor (FT) is a common type of functional movement disorder (FMD), which falls under the broader category of Functional Neurological Disorder (FND). This condition involves uncontrollable shaking of a body part, often an arm or a leg, that results from a temporary problem in the nervous system’s signaling rather than damage to the brain’s structure. The symptoms are genuine and involuntary, meaning the person experiencing the tremor is not consciously producing the movement. FT represents a disruption in the way the brain sends and receives signals, which can be conceptually understood as a “software” issue rather than a “hardware” failure like a stroke or multiple sclerosis.
Defining Functional Tremor
Functional tremor is defined by the absence of an underlying structural or neurodegenerative disease that would typically explain the persistent movement disorder. Unlike other tremors, the issue is not related to the death of nerve cells, such as in Parkinson’s disease, or a structural lesion in the brain. The term “functional” highlights that the normal function of the nervous system is altered, even though diagnostic scans like MRI often show a structurally healthy brain. FT is the most frequently reported type of functional movement disorder.
The mechanism of FT involves a temporary and potentially reversible problem in how the brain processes movement signals. This differs significantly from Essential Tremor or Parkinsonian Tremor, which have distinct neurological causes. Because the issue is functional, not degenerative, the condition can sometimes improve or even resolve completely. The diagnosis is based on the recognition of specific positive clinical signs rather than merely ruling out other neurological diseases.
Recognizing Characteristic Clinical Signs
The diagnosis of functional tremor relies heavily on identifying several positive clinical signs during a neurological examination that are incongruent with organic tremors.
Variability
One of the most telling signs is variability, where the tremor can change markedly in its frequency, amplitude (strength), or direction, even within a short period. This fluctuation is unusual in tremors caused by structural brain diseases.
Distractibility
The tremor decreases significantly or stops entirely when the patient’s attention is diverted away from the affected limb, such as by performing a complex mental task.
Entrainment
A key diagnostic feature is entrainment, where the tremor in the affected limb takes on the exact rhythm and frequency of a movement performed by the unaffected limb, such as tapping a foot or hand. This response to external rhythm is considered a “rule-in” sign for functional tremor.
Co-activation Sign
This involves the simultaneous contraction of opposing muscle groups (antagonists and agonists) when the patient attempts to move. This pattern is not typically seen in organic tremors.
The onset of the tremor is often sudden, and its course is frequently marked by fluctuations, including periods of spontaneous remission. These distinctive physical manifestations allow neurologists to make a confident, positive diagnosis.
Understanding the Underlying Factors
The development of functional tremor often involves a combination of predisposing factors and a precipitating event that triggers the onset of symptoms. The condition is not simply a psychological disorder, but rather a neurological one where the brain’s wiring for movement is temporarily reset. This neurological “software” error can be triggered by various events, which fundamentally alter how the brain controls and perceives movement.
Physical precipitating events are very common and can include a minor physical injury to the limb, surgery, a non-neurological infection, or a side effect from a medication. Acute psychological stressors, like a panic attack or an emotionally traumatic event, can also act as the trigger. Psychological vulnerability, such as a history of high stress, anxiety, or trauma, is a risk factor, but it is not a prerequisite. The model suggests that a person with a predisposition experiences a triggering event, which then leads to a maladaptive shift in brain network function, resulting in the involuntary tremor.
Management and Treatment Approaches
Effective management of functional tremor is multidisciplinary, starting with receiving a clear, affirmative diagnosis and a comprehensive explanation of the condition from a neurologist. Understanding that the symptoms are real and physical, caused by a reversible nervous system problem, is a therapeutic step in itself. Treatment typically focuses on motor retraining through specialized physical therapy, aiming to normalize the disrupted movement patterns.
Physical therapists use techniques that involve redirection of attention and breaking the entrainment pattern to re-establish normal motor control. They may use external cues, like rhythmic auditory stimulation, to guide the patient toward a controlled, non-tremulous movement. Psychological interventions, such as Cognitive Behavioral Therapy (CBT), are often used in parallel to address underlying risk factors like hypervigilance, anxiety, or maladaptive thoughts that may be sustaining the tremor. Studies have shown that CBT can significantly reduce tremor severity. Traditional tremor medications, which target neurodegenerative disorders, usually have a limited role in treating functional tremor.