2.3.2 Parkinsonian tremor
Symptoms
Parkinsonian tremor (PT) is a symptom of Parkinson's disease (PD). 80 to 90 percent of patients develop PT during the course of PD (Smaga, 2003). PT typically shows as a resting tremor in the forearms and up to 20% of PD patients also exhibit postural or kinetic tremor (Rubchinsky, Kuznetsov, Wheelock, & Sigvardt, 2007). Other symptoms of PD are rigidity, bradykinesia and impaired postural reflexes (Smaga, 2003). The amplitude of PT increases with stress and diminishes with voluntary movement (Smaga, 2003). Onset of PD is usually after the age of 60 (Van den Eden, et al., 2003).
Frequency range of oscillation
The frequency of oscillation of PT has been reported to be between 4 Hz and 6 Hz (Smaga, 2003), 4 Hz and 5Hz (Eidelberg & Pourfar, 2007), 3 Hz and 8 Hz (Harish, Venkateswara Rao, Borgohain, Sairam, & Abhilash, 2009), and 3 Hz and 7 Hz (Rubchinsky, Kuznetsov, Wheelock, & Sigvardt, 2007). Proprioceptive feedback appears to modify the frequency of the tremor (Pollock & Davis, 1930; Hassler, 1970; Rack and Ross, 1986) uit SP***) (Burne, 1987). Apparently there is no consensus on the frequency of oscillation of PT.
Prevalence
PT has a prevalence of 102-190 cases per 100,000 population in Western countries (Rubchinsky, Kuznetsov, Wheelock, & Sigvardt, 2007).
Etiology
The etiology of PD is yet unknown. Usually there is no family history (Ahmed & Sweeney, 2002).
Pathology
PD is characterized by the severe degeneration of dopaminergic neurons in the basal ganglia (Grimaldi & Manto, Tremor: From Pathogenesis to Treatment, 2008) (Rubchinsky, Kuznetsov, Wheelock, & Sigvardt, 2007), which are the main source of the neurotransmitter dopamine. The location of the oscillator remains unknown, but there is a consensus on the existence of a central tremor generator in PT (Rubchinsky, Kuznetsov, Wheelock, & Sigvardt, 2007). There are several hypotheses, but the most frequently proposed one is the basal ganglia-thalamo-cortical loop hypothesis (Burne, 1987). ***uitleg in http://www.ncbi.nlm.nih.gov/pubmed/8511438
***"A basal ganglia-thalamus-cortical loop has most frequently been proposed. Implicit in this theory is the notion that the central oscillator would determine tremor amplitude and frequency by periodic inputs to the motor neurons through descending motor pathways [reviewed by Young (24)]." (Burne, 1987)
Treatment
To compensate for the lack of dopamine, dopaminergic therapy can be applied to PD patients, which results in improved motor behavior. However, dopaminergic therapy loses its effectiveness over time and although adjusting the medication can recover the effectiveness, 10 to 20 percent of PD patients have to undergo surgical treatment (Rubchinsky, Kuznetsov, Wheelock, & Sigvardt, 2007). The most common procedure is the placement of a deep brain stimulator (Benabid, 2003)(***uit SP). ***DBS uitleggen***boek G&M***. Although risks are involved, the advantage of a deep brain stimulator is that its actions do no permanent damage, so adjustment of location and signal intensity is possible. Is some cases a thalamotomy is performed, in which case a part of the thalamus is surgically destroyed, which causes irreversible damage (Hua, Garonzik, Lee, & Lenz, 2003).
2.3.3 Cerebellar tremor
Symptoms
Cerebellar is an intention tremor, which may include a postural tremor of the trunk and neck (Smaga, 2003) (Tremor fact sheet, 2006). Symptoms which may also be present are dysarthria (speech problems), nystagmus (rapid rolling of the eyes) and gait problems (Tremor fact sheet, 2006).
Frequency range of oscillation
The frequency of oscillation of cerebellar tremor is reported to be less than 5 Hz (Smaga, 2003), between 3 and 5 Hz (Seeberger, 2005)(***SP) and between 2.5 Hz and 4 Hz (Charles, Esper, Davis, Maciunas, & Robertson, 1999) The possible postural tremor has a higher frequency of up to 10 Hz (Charles, Esper, Davis, Maciunas, & Robertson, 1999).
Prevalence
No prevalence numbers could be found for cerebellar tremor.
Etiology
Cerebellar tremor is caused by stroke, brainstem tumor, multiple sclerosis (Smaga, 2003) and degenerative diseases of the cerebellum (Seeberger, 2005). Cerebellar tremor can also result from chronic alcoholism or overuse of some medicines (Tremor fact sheet, 2006).
Pathology
The cerebellum is involved in movement in the following ways:
- Receptors like muscle spindles send information to the cerebellum which allows the adjustment of the movement.
- The motor cortex sends the muscle activation command also to the cerebellum (called efferent copy), so the cerebellum can send short loop corrections back to the cortex during the movement.
- The cerebellum can send a motor sequence plan of learned movements to the motor cortex which allows for fast complicated movements.
Cerebellar tremor is probably caused by the dysfunction of one or more of these mechanisms (Seeberger, 2005).
Treatment
Several types of medication have some benefit on cerebellar tremor, but little studies have been performed on their effectiveness. Deep brain stimulation and thalamotomy have also successfully been used on cerebellar tremor patients (Seeberger, 2005).
