Medical Device Daily Contributing Writer

Physicians on staff at Marshfield Clinic at Saint Joseph's Hospital (Marshfield, Wisconsin) recently presented a webcast presenting the sophisticated treatment options now available to alleviate tremor disorders and featuring a pre–taped deep brain stimulation (DBS) procedure and real–time panel discussion.

The Neurosciences Department at Marshfield Clinic includes a team of neuro–specialists: John Neal, MD, performing and coordinating the procedure; Daniel Sa, MD, selecting appropriate patients, and aiding in electrode placement by microelectrode recording; John Ehrfurth, PhD, performing evaluations to predict side effects; and Mahala Earnhart, RN, coordinates care and pacemaker programming. The webcast panel included moderator Jaime Bolero, MD, Neal and Sa.

Bolero described patients with persistent tremors as "very limited in their social activity — they really cannot do much because the tremors are constant and they must always take medication."

And Sa said DBS "can be used for a number of different types of tremor, but Parkinson's is the most common disease for this surgery. He said that research has found that Parkinson's "is more than one disease; different genes cause different varieties. Many times we don't know the exact cause. We see changes as brain cells die and cease the production of dopamine. The lack of dopamine at the brain cell connections causes symptoms of shaking, stiffness and slowness."

He said initial treatment is via medication, but the diseases progresses, producing motor function fluctuations and "making it difficult to do anything except, perhaps, a couple hours of activity, with much effort." Typical are dyskinesias, involuntary movement of the limbs, with the level of disability key to DBS candidacy: essentially limitation on the person's ability to work or pursue important leisure activities.

"Eventually," Sa said, "the motor function fluctuations become too common and surgery must be considered. Different tremor types require different target locations. We target the brain in one single spot with this technique."

The procedure is reversible "and we've seen no long–term side effects. The treatment can be stopped, if needed. The patient's situation then returns to pre–stimulation levels of tremor."

Implanting a deep brain stimulator involves precise electrode placement within the thalamus, an area of the brain controlling muscle function. The electrodes are connected to a battery pack/pulse generator, with a computer programming and controlling stimulation via electrical signals.

The pulse generator, about the size of a cardiac pacemaker, is implanted within the body but can be turned on and off by the patient using a hand–held magnet. The four probes of the device are programmed individually, with the amount of stimulation varied as the disease evolves.

An e–mailed question: "How did we get to this knowledge of a specific place in the brain causing the tremor?"

Neal said that in 1940, a patient scheduled for neurosurgery for aneurysm clipping had a significant tremor and that during the surgery the artery to the thalamus "was sacrificed — post–operatively his tremor was gone."

Instruments for the procedure were approved in the 1990s in Europe and in the past 10 years in the U.S. Since then, "We've seen an explosion of technology ... ."

An Internet listener, a 36–year–old, with Parkinson's for 10 years, no longer responding to medication, asked if he should consider DBS.

That depends on the patient's "exact situation," Sa said. "We take a very individual approach and you certainly may be a candidate for DBS."

Neal said procedural success is reduced "if dementia is already present. Those patients will be even more confused post–surgery. We do a series of neurophysiologic tests to screen for cognitive problems or dementia. Other speech problems will not improve. When there are walking problems, some patients get better and some get worse."

Sa said that the clinic has treated hundreds of patients with no complications, though "a probe placed into the brain can cause bleeding which can theoretically lead to stroke or paralysis. Hardware failure and infection could occur. We've seen only one very minor infection and a small number of hardware complications. Of our cases, 95+% do well, but there are no guarantees."

Neal introduced the video of a DBS procedure. "First we see the placement of the stereotactic head frame. The patient receives local anesthesia so we can constantly monitor his comfort level and watch for therapeutic benefits and side effects.

"An anesthesiologist monitors the patient's signs and symptoms and controls the level of pain experienced." Next, three markers are placed on the skull, showing up on MRI to target the spot in the brain using Cartesian coordinates. The frame, bolted to the operating table, holds the patient's head absolutely still. Computer software is used to program the stimulator.

A hole is drilled through the skull, and Neal says, "Once the cranium is perforated, we open the dura and can access the target. A series of cannulas are used to introduce the microelectrode to localize the target spot. The cannula is gently moved deeper down into the brain to the approximate level of the thalamus.

Sa explained: "How do we make sure we are in the right place? First we use a machine much like a videogame joy stick, slowly lowering the electrode through different parts of the brain... a very slow progression. We can see the electrical output of the neurons being measured by the computer and we listen to the sounds they make to try to identify the correct part of the brain.

"Different types of neurons respond with different sounds. We are collecting electrical information from the neurons firing in the brain to find a certain amount of cells along a 3 mm line for our target. The subthalamic nucleus neurons put out a very different sound than sounds from other parts of the brain."

When the physicians have determined they are in the target spot, the stimulator is activated and the patient is monitored. The tremor stops, and when the stimulator is turned off, it returns. After recording the electrode placement and results, the cannula is removed, leaving the electrode in place. The wound is closed.

Neal said the procedure doesn't cure but has "a remarkable effect, as you've just seen." The procedure reduces symptoms "but the disease continues to progress over time. The device allows for variation of the electrodes as the disease progresses and changes. We can help the patient adapt to his disease over time without additional procedures."