An intention, rubral, cerebellar, or course tremor is defined as a rhythmic, oscillatory, and high amplitude tremor during a directed and purposeful motor movement, worsening before reaching the target. It is due to cerebellar dysfunction. It can affect precision in coordinated movements of speech muscles and limbs. The cerebellum, along with its sensory-motor white matter tracts, is responsible for motor coordination, posture and balance. The feedback mechanisms between the cerebellum, the cortex, and the brainstem become impaired, leading to kinetic errors, more prominent in fine motor skill tasks.
Intention tremor was first described by Jean-Martin Charcot in 1868, who noticed that multiple sclerosis (MS) patients could be differentiated from Parkinson disease (PD) patients by the type of tremor they present. MS is the most common cause of intention tremor. MS patients had intention tremors along with nystagmus and scanning speech, bearing his name as the Charcot's triad.
There are various causes of intention tremors:
The epidemiology of intention tremor is challenging to ascertain, as it can be present in various disease at a different rate. Intention tremors can be present 9 % in head, 50% in the arms, and 27% in the legs. Up to 38.5% of the patients with essential tremor can also have intention tremor and is correlated with a longer duration of the essential tremor and a younger age for the onset of the tremor. Prevalence can be as high as 44% of those patients with essential tremor. Intention tremor is very rarely (4%) present in PD.
In intention tremor, the central nervous system cerebellar feedback and error control centers are impaired. The relay system between the cerebellum and efferent muscle can be compromised, resulting in the action tremor. It is associated with damage to the superior cerebellar peduncle, dentate nucleus, and surrounding cerebellar tracts in the brainstem and the thalamus. Thalamic nuclei involvement and feedback had also been implicated and are used as a neurophysiological basis for treatment management.
A toxic disorder that is useful to examine the neuropathology of cerebellar degeneration is an alcohol abuse disorder. In a true alcoholic patient, cerebellar degeneration disorders involve Purkinje cells, including the molecular cell layer, with a distinct distribution, predominant in the anterior vermis.
Patients with intention tremors usually complain of difficulties with activities of daily living, including drinking from a cup, grabbing utensils to eat, problems with coordination eye to an object, and problems with ambulation. Associated cerebellar signs can include nystagmus, dysmetria, dysdiadochokinesia, hypotonia, proprioception deficits, and gait ataxia.
Magnetic resonance imaging (MRI) is the gold standard study to evaluate the brain and cerebellum. Many of the etiologies will be identified by this study.
Specific etiologies should be evaluated as follows:
Physiological/psychiatric: a good history and physical, complete metabolic panel (CMP), psychiatric history, nonpharmacological management, stressful situations (anxiety, fear, anger, and fatigue).
Iatrogenic: a thorough review of home medications and establish a timeline to determine whether starting or discontinuing any particular medication could have triggered the tremor.
Vascular: a comprehensive stroke workup including a good history and physical, screening of vascular risk factors, A1C, lipid panel, blood pressure measurements, brain and vessel imaging (head computed tomographic (CT) scan, head CT angiography, CT perfusion, brain MRI), 2D Echocardiogram with bubble study, Holter monitoring.
Trauma: a CMP, complete blood count (CBC), coagulation studies, head CT scan, CT angiography, brain MRI, MR venous, electromyography, or nerve conduction.
Neuroinflammatory, autoimmune or paraneoplastic: CMP, CBC, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), antinuclear antibodies, extractable nuclear antigen panel, Sjogren and lupus anticoagulant studies, antineutrophil cytoplasmic antibodies, angiotensin-converting enzyme test, head CT, brain and spine MRI, chest/abdomen/pelvis CT scan, and lumbar puncture with laboratory studies including cells with differential, glucose, protein, IgG index, myelin basic protein, oligoclonal bands, aquaporin four antibodies, myelin oligodendrocyte glycoprotein antibodies, paraneoplastic panel, flow cytometry/cytology.
Metabolic: CBC, CMP, vitamin deficiency workup, ammonia level, liver ultrasound, abdomen/pelvis CT scan with contrast, advanced metabolic testing.
Toxic: urine toxicology, ethanol level, heavy metal testing.
Hereditary: CBC, CMP, ESR, CRP, copper/ceruloplasmin, slit eye lamp examination, head CT scan, brain MRI, genetic testing.
Treatment usually consists of treating the underlying disorder.
Noninvasive techniques: Include gait rehabilitation, visually guided techniques, tendon vibration, weighting extremities, positioning techniques, and manual techniques, all of which can be useful for the recovery of functional activities.
Pharmacological treatment: There is no specific recommended treatment for intention tremor. Isoniazid is the most commonly used for patients with MS with results in about half of the patients, but others like botulinum toxin A, levetiracetam, 4-amino-pyridine, cannabis had been used.
Invasive techniques: Thalamic deep brain stimulation can alleviate the tremor in MS, providing better functional performance. Stereotactic radiosurgery thalamotomy at the nucleus ventralis intermedius with a median maximum dose of 140 Gy also provides good functional outcomes in patients with MS. Radiofrequency thalamotomy had been successfully used in the past but has been replaced with the newer techniques of radiosurgery and deep brain stimulation as they had fewer adverse effects.
The differential diagnosis for intention tremor is physiological (essential tremor). Up to 38.5% of the patients with essential tremor can also have intention tremor.
The different etiologies have to be differentiated as they have divergent management. Iatrogenic (medication use) causes being the most common; however, serum laboratories, brain imaging, and cerebrospinal fluid studies may be used to distinguish between metabolic, neuroinfectious, neuroinflammatory, and paraneoplastic etiologies.
The prognosis is dependent on the etiology of the intention tremor, but with rehabilitation, non-pharmacological, and pharmacological interventions, it should improve gradually. Permanent damage to cerebellar structures and tracts may cause irreversible dysmetria and intention tremors.
If the underlying cause is not addressed, intention tremors can lead to impairments in functional activities of daily living, which can be very frustrating for patients. On the bright side, there are no known life-threatening complications from intention tremors.
Healthcare providers from the following department should be on-board while managing the patient with intention tremors:
Patients should be advised that if clinical symptoms are acute, they should seek care at the emergency room to rule out life-threatening diagnoses such as ischemic stroke and malignancy. If symptoms are gradual or intermittent, they should visit their primary care physician for a referral to a neurologist for evaluation and management.
Here are some important points to take into consideration:
At this time, there is no evidence-based study that guides the creation of an interdisciplinary team for intention tremor. However, a neurologist, movement disorder specialist, physical and occupational therapist, social worker, and geneticist should be consulted to provide the best care and quality of life for a patient and to inform medical decisions regarding long-term care. [Level 5]
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