Hello Friends,
 
The continuing story of thalamic Stimulation. I typed this from a brochure
from the company Medtronic called : "Thalamic Stimulation System, Therapy
Reference Guide"
 
 
Section 1 : OVERVIEW OF THALAMIC STIMULATION FOR TREATMENT OF TREMOR
 
Uses and patients Benefits
 
Stimulation of the ventral intermediate (VIM) nucleus of the thalamus
(figure 1; it shows a picture of a head, with the spot where the lead is
implanted) is indicated as a therapy for patients with disabling tremor who
are not suitable candidates for drug therapy or whose tremor has not been
adequately controlled by drug therapy
 
Many patients treated with thalamic stimulation gain substantial control
over otherwise refractory tremor.  their quality of life improves  as they
are able to participate more fully in daily activities.
 
 
Definition: tremor
 
Tremor is defined as the rhytmic, oscillating  movements of a body part due
to repetitive patterns of muscle contraction and relaxation. It is
classified as :
 
*       Rest tremor -- occurs during rest
*       Postural tremor --occurs when limbs are upright (working against
gravity)
*       Kinetic tremor -- occurs during limb movement
 
The origin of tremor is thought to be in the brain.Stimulation of the VIM
nucleus inhibits  tremor, Allthough the exact mechanism is unknown.
 
Tremor is a prominent signof Parkinson's disease (PD) and the only sign of
essential tremor (ET), both of which can be treated with thalamic
stimulation. Rest tremor is pathognomonic for PD, allthough postural tremor
is not uncommon. In severe cases of PD, rest and postural tremor (mixed
tremor) may be manifest. Postural tremor is typical of essential tremor,
allthough kinetic tremor may also be present.
 
Tremor Therapy
 
Tremor is effectively managed pharmacologically in the majority of patients.
When tremor becomes medically intractable and severly disabling, stimulation
of the VIM nucleus may provide relief. Thalamic stimulation is non
destructive and reversible. It can be used to treat bilateral tremor.
The tremor-suppressing effect of thaamic stimulation have known since the
1920's. Very llittle, however, is known about the mechamism of action.
According to Benabid et al. (1993), thalamic stimulation does not appear to
suppress tremor by an excitatory or inhibitory effect. Rather, it is more
likely that tremor supprression results from jamming the neuronal  network
processing proprioceptive inputs to the thalamus.
 
 
Stimulation Test
 
Patients are tested for tremor suppression typically as a first step in the
stimulation system implant procedure. A test electrode is stereotactically
placed in the brain to locate the target site. Then an external stimulator,
such as the model 3625 Screener, is used to determine whether or not
stimulation suppresses the tremor. If no tremor suppression occurs, the
implant procedure is discontinued. If the tremor is suppressed
satisfactorily, the model 3387 lead is implanted. The physician then has the
option of either implanting the IPG immediately after the lead is implanted
or using the screener for a trial period before implanting the IPG.
 
Thalamic stimulation System
 
To perform thalamic stimulation for the treatment of tremor, Medtronic
provides a system of components consisting of an implantable pulse generator
(IPG), lead, extension and external programmer (table 1; An overview of the
components)
 
 
Therapeutic Efficacy
 
Clinical studies show that thalamic stimulation is effective in treating
tremor. Table 2 summaries the clinical results.
 
(to be continued)