ESSENTIAL TREMOR: SURGERY

There are currently two operations that are done for the treatment of tremor in general and essential tremor in particular, namely thalamotomy and deep brain stimulation (DBS). The initial steps of both procedures are identical. Both are performed using stereotactic surgery (described below). The initial steps of both procedures are identical.

Thalamotomy
Thalamotomy is an operation that has been used for more than 40 years for the treatment of tremor. Thalamotomy involves placing a small lesion in the ventral intermediate nucleus of the thalamus or VIM. This area is roughly the size and thickness of a dime. After applying the stereotactic frame and obtaining an MRI scan to locate the target, the patient is brought to the operating room for the procedure. An intravenous is started and monitors applied so that the anesthesiologist can accurately monitor the blood pressure during the operation. The operation is done with the patient awake but is not painful. It is crucial that the patient be awake in order to cooperate with testing during the procedure. The scalp is numbed using local anesthetic and a small incision is made. A small hole is then drilled in the skull bone.

A small probe is then passed through the brain and positioned in VIM. Intraoperative testing is performed to verify that the probe is in the correct location since VIM is very close to several other very important areas in the brain. Once the neurosurgeon is confident of the position, the probe is connected to a special machine called a lesion generator and a series of lesions is made using a technique known as radiofrequency thermal coagulation. Basically, energy very similar to microwaves is passed through the probe. This energy heats a spherical area of brain tissue surrounding the probe and destroys the nerve cells that are responsible for producing the tremor. The size of the lesion can be precisely controlled by monitoring the temperature of the probe and the time of the lesion. During the lesioning process, the patient is continuously checked to make certain that the tremor goes away and that no adverse side effects occur. Once the lesions are completed, the probe is removed from the brain, and the small incision is sutured. Once the patient arrive in the operating room, the total length of the procedure is around 1 hour. After the procedure is completed, the patient is observed overnight in the hospital and usually discharged the following day.

Although thalamotomy is a safe procedure, there are some risks. The possible complications of thalamotomy include hemorrhage (bleeding in the brain), infection, contralateral hemiparesis (weakness), dysarthria (slurring of speech), and contralateral sensory loss. The most serious complication is hemorrhage, but fortunately this is rare. The other complications are usually transient and resolve over a period of a few days to several weeks.

Deep Brain Stimulation
Deep brain stimulation was introduced in the late 1960s and 1970s for the treatment of pain. Over the years during the "testing" period that is always performed during thalamotomy, it was noted that high frequency electrical stimulation could abolish the tremor. Consequently, DBS for the treatment of tremor evolved from observations made during thalamotomy. DBS has been used for the past decade and about 3 years ago thalamic DBS was approved by the FDA for the treatment of tremor.

DBS and thalamotomy are quite similar. In fact, the two operations are done in the exact same fashion up until the point at which a lesion would be made for a thalamotomy. With DBS, instead of making a lesion, a thin wire called an electrode is inserted into VIM and small pulses of electricity are sent through the wire. The electrical stimulation blocks the abnormal signals coming from the brain and the tremor ceases. Once the wire is in the proper position, it is anchored to a plastic cap that fits inside the hole that is drilled in the skull. The wire is then connected to a an implantable pulse generator (IPG) which is placed under the skin just beneath the collarbone. The IPG is a battery that tells the electrode how to deliver the electrical pulses to the brain. The IPG can be programmed using a laptop computer and a wand which is held over the unit. No part of the system is visible; that is, everything lies below the skin. Again, the patient remains in the hospital, usually just overnight and may go home the following morning. The risks of DBS are very similar to those that can occur with thalamotomy. Possible complications include hemorrhage, infection, contralateral hemiparesis, dysarthria, paresthesias, headache, disturbance of balance. Paresthesias are usually transient and can often be eliminated if they occur by reprogramming the stimulator. About 6 % of patients may be mild constant paresthesias that are permanent. The IPG unit is a battery and as such needs to be replaced, usually every 3-5 years. This is a minor outpatient procedure that can be performed under local anesthesia.

Thalamotomy versus Deep Brain Stimulation
The natural question that most patients have is "how does the neurosurgeon decide whether to perform a thalamotomy or DBS?" First, it is important to understand that both procedures are about equally effective in eliminating or significantly reducing tremor. However, there are relative advantages and drawbacks to both and it is necessary for the neurosurgeon and patient to carefully weigh these issues before deciding on a particular operation.

Thalamotomy is a highly effective procedure. Once the operation is done, the patient does not need to have extensive follow-up (aside from intermittent visits to ensure that the procedure is still effective). There is no implanted device that needs to be programmed or replaced. In contrast, patients with DBS need to have more frequent follow-up visits to reprogram the stimulator. This may very difficult for some patients who may live long distances. Thalamotomy is considered to be what is called an ablative procedure; in other words, a lesion is made that destroys the abnormal nerve cells. The effects produced by thalamotomy are not reversible. Thalamotomy can only be performed on a single side of the brain. Bilateral thalamotomy is not recommended since there is a significant chance of disabling speech and/or swallowing problems.

The main advantage of DBS is the fact that it is n reversible and non-destructive. DBS also offers the ability to adjust or "fine tune" the stimulation to achieve optimal tremor control. The major disadvantage is that some patients do require frequent visits for programming and eventually the IPG needs to be replaced. DBS also offers the option of treating bilateral tremor.