Intention Tremor · What Is It, Causes, Diagnosis, Treatment, and More

Intention tremors are involuntary, rhythmic muscle contractions (i.e., oscillations) that occur during a purposeful, voluntary movement. The oscillations’ amplitude typically worsens as the movement proceeds, meaning that the tremor increases in intensity upon reaching a target. 

More generally, a tremor refers to any rhythmic and involuntary movements associated with one or more parts of the body. There are several different types of tremors and intention tremors are classified as a common type of kinetic tremor, which is any tremor occurring during a voluntary movement. Kinetic tremors can be further categorized as action tremors, meaning they appear during physical actions. The affected parts of the body are usually the limbs—most often the upper limbs—or the speech muscles. 

The most common cause of intention tremors is multiple sclerosis (MS), an autoimmune, inflammatory disorder that affects the protective coverings (i.e., myelin sheath) of nerves in the central nervous system impacting the communication between the brain and the rest of the body. 

Alternatively, many cases of intention tremors are caused by dysfunction and lesions of the cerebellum (e.g., stroke, traumatic brain injury, tumors, or neurodegeneration disorders), inducing what is known as a cerebellar tremor. The cerebellum is a small structure behind the brainstem that coordinates voluntary movement, posture, and balance, among other functions. When the feedback mechanisms and collaboration between the cerebellum and other structures of the central nervous system are impaired, errors in movement execution and consequent intention tremors can occur. Strokes or trauma to the midbrain (i.e., part of the brainstem) can also cause an intention tremor.   

Other causes include hereditary disorders, such as Wilson disease, or metabolic conditions, such as hepatocerebral degeneration, often occurring in individuals with chronic liver damage. Physiological or psychological conditions, such as anxiety, anger, and fatigue, can also lead to an intention tremor known as a psychogenic tremor. Additionally, overexposure to toxic substances (e.g., alcohol dependence, mercury poisoning, etc.) can also potentially lead to intention tremors. Lastly, certain medications could also result in a drug-induced tremor. 

Diagnosis of intention tremors usually requires an assessment of medical history and a complete neurological examination. Firstly, to identify the intention tremor, two different tests may be performed: the heel-to-shin test assesses the presence of cerebellar lesions by examining the ability to move one's heel from below the knee of the opposite leg, down to the foot; and the finger-to-nose test helps identify the presence of an intention tremor and consists of moving the individual’s finger from the individual’s nose to the examiner’s finger positioned in front of them. 

Further assessment of other signs and symptoms, such as abnormalities in manner of walking (i.e., gait); difficulties in completing daily activities, like drinking or eating with utensils; and problems with hand-eye coordination, can be helpful in determining the specific cause of the tremor. Other apparent signs of cerebellar dysfunction can include rapid involuntary eye movements (i.e., nystagmus), low muscle tone (i.e., hypotonia), inability to control the range of motion of a movement (i.e., dysmetria), and impaired ability to perform quick alternating movements (i.e., dysdiadochokinesia), among others. A review of past medications is also important to identify any potential triggers for the tremor. Imaging techniques, such as magnetic resonance imaging (MRI), may also be performed. Depending on the suspected cause, further differential diagnostic testing, such as echocardiograms, blood tests, and nerve conduction studies, could also be conducted. 

Further assessment of other signs and symptoms, such as abnormalities in manner of walking (gait), difficulties in completing daily activities, like drinking or eating with utensils, and problems with hand-eye coordination, can be helpful in determining the specific cause of the tremor. Other apparent signs of cerebellar dysfunction can include rapid involuntary eye movements (nystagmus), low muscle tone (hypotonia), impaired ability to perform quick alternating movements (dysdiadochokinesia), among others. A review of past medications is also important to identify any potential triggers for the tremors. Imaging techniques, such as magnetic resonance imaging (MRI), may also be performed. Depending on the suspected cause, further differential diagnostic testing, such as echocardiograms, blood tests, and nerve conduction studies, may also be performed.

Treatment of intention tremors primarily focuses on treating the underlying cause. For example, if it is suspected that a particular medication may have caused the tremor, the clinician may suggest discontinuing that medication.  

In addition, individuals with intention tremors may improve their ability to perform functional activities through supportive treatment, such as gait rehabilitation, physical therapy, wearing wrist weights, as well as relaxation and positioning techniques.  

Medications are generally not prescribed to treat intention tremors, however in some cases of MS, certain medications (e.g., isoniazid) have been found to help reduce the tremors. MS-induced tremors may also require more invasive procedures, such as radiosurgery, which uses radiation in surgical procedures, or thalamic deep brain stimulation (DBS), which involves implantation of electrodes in specific brain structures.