Fortunately, DBS has been developed and was approved in 1997
for electrode placement in the Vim nucleus of the thalamus for
treatment of tremor. The invention of DBS provided for the first
time The potential for bilateral treatment in patients who
receive either unilateral lesional surgery followed by DBS on the
contralateral side or bilateral stimulation systems.
The issue of bilateral surgery is important since bilateral
symptoms are seen in almost all patients.The best candidate for
pallidal surgery will be the patient who is younger than 70
years; however, a patient older than 70 years but who is in good
medical health also appears to be a reasonable candidate. The
patient must show some response to dopaminergic medications as
well as evidence of poor control of their symptoms and preferably
show drug-induced dyskinesias. The patient in whom the main
symptom is difficulty with walking and balance or dysarthria
tends to be a poor candidate for the procedure as well as the
patient with Parkinson's plus syndromes, with severe dementia, or
who shows no evidence of dyskinesias. Tremor-predominant patients
are better candidates for a thalamic procedure rather than
pallidotomy since the thalamic intervention provides more
effective management of the tremor.
If essential tremor is present, the evaluation is in some ways
simpler. Essential tremor tends to be a bilateral process and is
characterized by slow rhythmic tremor, particularly of the upper
extremities. Often, the disease has a genetic basis and family
members will relate other ancestors who have had similar
symptoms. An easy test for the diagnosis of essential tremor is
the alcohol test, in which the patient notes a decrease or even
abolition in their tremor following a small drink of alcohol.
Frequently,a doctor may recommend that these patients have a
small drink of wine or other alcoholic beverage at dinnertime so
as to decrease the tremor, making mealtimes more manageable.
These patients are often severely limited and incapacitated by
tremor.In these patients, pallidal intervention is not the
solution since the thalamic nuclei (in particular, the Vim
nuclei) are the preferred targets for treatment of their tremor.
Since the patient's symptoms are usually bilateral and because
previous research has demonstrated that bilateral thalamotomy
carries a high risk of side effects, it is recommended that these
patients undergo either placement of a bilateral DBS or
unilateral thalamotomy followed by a contralateral DBS placement
in the thalamus.
PREOPERATIVE
REQUIREMENTS
For the patient undergoing stereotactic lesional or DBS surgery,
it is best to have medications related to the movement disorder
treatment discontinued at least by midnight the day prior. This
is particularly important for the patient with severe dyskinesias
since it can interfere tremendously, not only intraoperatively
but also with frame placement and imaging for target
localization.
Persistence of the movement disorder (except for dyskinesia)
intraoperatively facilitates the evaluation of the effectiveness
of the stimulation and subsequent lesioning. It is imperative
that the patient cease taking any medications related to blood
coagulation. If a patient is required to be on oral
anticoagulants, we admit the patient 5-6 days prior to surgery,
discontinue the oral anticoagulants, and then place the patient
on intravenous heparin which is then stopped 6 hours prior to
surgery. Aspirin and nonsteroidal anti-inflammatory medications
are also stopped 2 weeks prior to surgery. To avoid the risk of
intraoperative hemorrhage, it is critical that the patient be
maintained on antihypertensive medications, and to avoid
postoperative hemorrhage, the patient's blood pressure must be
monitored intraoperatively and postoperatively, particularly
after lesional surgery. Other preoperative orders are those usual
for operative procedures (complete bloodcount, Chem-7,
prothrombin time/partial thromboplastin time, EKG, chest x-ray)
and the need for the patient to be rendered nothing by mouth
after midnight prior to surgery.
OPERATIVE PROCEDURE
In this discussion, the operative procedure is divided into four
main phases: placement of the stereotactic frame,
three-dimensional volumetric imaging, stereotactic planning with
computer software, and surgical treatment that includes
stimulation testing followed by lesioning surgery in the case of
pallidotomy or thalamotomy versus implantation of the DBS
electrode system in stimulation patients.
Placement of the Stereotactic
Frame
We routinely utilize the Ieksell stereotactic frame because of
its high level of stereotactic localization accuracy (on the
order of 100-200 µ). We have found that imaging and its analysis
preoperatively is critical, increasing efficiency, effectiveness,
and safetyand decreasing operative time. Because of extensive
evaluation at the imaging portion of the planning, the surgical
procedure itself does not require excessive amounts of time and,
in many cases, macro-stimulation techniques can be utilized
rather than microrecording.
The stereotactic Leksell frame is fixated to the patient prior
to beginning any portion of the surgical intervention (Figures 1
and 2). We prefer to perform this in a separate small operating
suite outside of our magnetic resonance imaging (MRI) center,
with the patient sedated by a neuroanesthesiologist. Although few
centers utilize this technique, we have found it imperative in
order to obtain very high-quality imaging utilizing our
three-dimensional (3D) volumetric matrix acquisition MRI system.
Sedation
is utilized during the frame placement, shortening this to just a
few minutes and making the experience pain-free, and also during
the MRI process so that there is absolutely no motion. Numerous
medications may be used including Midazolam (1-6 mg) and Fentanyl
(50-125 mcg); however, our anesthesiologists tend to prefer the
use of intravenous Propofol because of its ability to act quicky
and to be turned off with the near complete disappearance of drug
within minutes after cessation of infusion.
Following sedation, the patient is placed in a seated position
and the Leksell frame is applied parallel to the known
localization of the anterior cornmissure-posterior commissure
(AC-PC) line. This is obtained by placing the frame using the
Leksell ear bars through the bottom hole of the three-hole
adapter and subsequently placing the alignment of the ear bar
holder at the 100 mark on the horizontal or Y axis of the frame.
The
frame is then aligned with Reid's line, with the lowest of the
three holes aligning with the external ear canal and the superior
border of the horizontal Y bar of the frame aligning with the
inferior orbital rim. Optimal attachment of the frame is
confirmed if the U-shaped oral opening of the frame rests easily
on the surgeon's finger placed on the tip of the nose of the
patient. The depth of the ear bars is determined by noting them
to be snug and in place. Particularly with the patient being
sedated, great care must be taken to avoid damage to the ear
canals by too forceful placement of the ear bars.
Sedation
is utilized during the frame placement, shortening this to just a
few minutes and making the experience pain-free, and also during
the MRI process so that there is absolutely no motion. Numerous
medications may be used including Midazolam (1-6 mg) and Fentanyl
(50-125 mcg); however, our anesthesiologists tend to prefer the
use of intravenous Propofol because of its ability to act quicky
and to be turned off with the near complete disappearance of drug
within minutes after cessation of infusion. 
The
frame is then aligned with Reid's line, with the lowest of the
three holes aligning with the external ear canal and the superior
border of the horizontal Y bar of the frame aligning with the
inferior orbital rim. Optimal attachment of the frame is
confirmed if the U-shaped oral opening of the frame rests easily
on the surgeon's finger placed on the tip of the nose of the
patient. The depth of the ear bars is determined by noting them
to be snug and in place. Particularly with the patient being
sedated, great care must be taken to avoid damage to the ear
canals by too forceful placement of the ear bars.