Intention tremor is a dyskinetic disorder characterized by a broad, coarse, and low-frequency (below 5 Hz) tremor evident during deliberate and visually-guided movement (hence the name intention tremor). An intention tremor is usually perpendicular to the direction of movement. When experiencing an intention tremor, one often overshoots or undershoots one's target, a condition known as dysmetria. Intention tremor is the result of dysfunction of the cerebellum, particularly on the same side as the tremor in the lateral zone, which controls visually guided movements. Depending on the location of cerebellar damage, these tremors can be either unilateral or bilateral. Several causes have been discovered to date, including damage or degradation of the cerebellum due to neurodegenerative diseases, trauma, tumor, stroke, or toxicity. Currently, no pharmacological treatment has been established, but some success has been seen using treatments designed for essential tremors.
Signs and symptoms Patients with intention tremors usually complain of difficulties with activities of daily living, including drinking from a cup, grabbing utensils to eat, and problems with coordination eye to an object or ambulation. Associated cerebellar signs can include nystagmus, dysmetria, dysdiadochokinesia, hypotonia, proprioception deficits, and gait ataxia.
Causes Intention tremors are common among individuals with multiple sclerosis (MS). One common symptom of MS is ataxia, a lack of coordinated muscle movement caused by cerebellar lesions characteristic of MS. The disease often destroys physical and cognitive function of individuals. Intention tremors can be a first sign of MS, since loss or deterioration of motor function and sensitivity are often one of the first symptoms of cerebellar lesions. Intention tremors have a variety of other recorded causes, as well, including a variety of neurological disorders, such as stroke, cerebral palsy, alcoholism, alcohol withdrawal, peripheral neuropathy, Wilson's disease, Creutzfeldt–Jakob disease, Guillain–Barré syndrome, and fragile X syndrome, as well as brain tumors, low blood sugar, hyperthyroidism, hypoparathyroidism, insulinoma, normal aging, and traumatic brain injury. Holmes tremor, a rubral or midbrain tremor, is another form of tremor that includes intention tremors, among other symptoms. This disease affects the proximal muscles of the head, shoulders, and neck. Tremors of this disease occur at frequencies of 2–4 Hz or more. Intention tremor is also known to be associated with infections, such as West Nile virus, rubella, H. influenza, rabies, and varicella. A variety of poisons have been shown to cause intention tremor, including mercury, methyl bromide, and phosphine. In addition, vitamin deficiencies have been linked to intention tremor, especially deficiency in vitamin E. Pharmacological agents such as anti-arrhythmic drugs, anti-epileptic agents, benzodiazepine, cyclosporine, lithium, neuroleptics, and stimulants have been known to cause intention tremor. Some ordinary activities, including ingesting too much caffeine, cigarettes, and alcohol, along with stress, anxiety, fear, anger, and fatigue have also been shown to cause intention tremor by negatively affecting the cerebellum, brainstem, or thalamus, as discussed in mechanisms.
Mechanism
Intention tremors that are caused by normal, everyday activities, such as stress, anxiety, fear, anger, caffeine, and fatigue, do not seem to result from damage to any part of the brain. These tremors, instead, seem to be a temporary worsening of a small tremor that is present in every human being. These tremors generally go away with time. More persistent intention tremors are often caused by damage to certain regions of the brain. Their most common cause is damage and/or degeneration in the cerebellum, the part of the brain responsible for motor coordination, posture, and balance, and especially fine motor movements. When the cerebellum is damaged, a person may have difficulty executing a fine motor movement, such as attempting to touch one's nose with one's finger. One common way for the cerebellum to become damaged is through the development of cerebellar lesions. The most common site for cerebellar lesions that lead to intention tremors has been reported to be the superior cerebellar peduncle, through which all fibers carrying information to the midbrain pass, and the dentate nucleus, which is also responsible for linking the cerebellum to the rest of the brain. Alcohol abuse is one typical cause of this damage to the cerebellum. The alcohol abuse causes degeneration of the anterior vermis of the cerebellum. This leads to an inability to process fine motor movements in the individual and the development of intention tremors. In MS, damage occurs due to demyelination and neuron death, which again produce cerebellar lesions and an inability for those neurons to transmit signals. Because of this tight association with damage to the cerebellum, intention tremors are often referred to as cerebellar tremors. Intention tremors can also be caused as a result of damage to the brainstem or thalamus. Both of these structures are involved in the transmission of information between the cerebellum and the cerebral cortex, and between the cerebellum and the spinal cord, and then on to the motor neurons. When these become damaged, the relay system between the cerebellum and the muscle upon which it is trying to act is compromised, resulting in the development of a tremor.
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