FALL 2007

Deep Brain Stimulation for Movement Disorders—and More

Parkinson’s disease is caused by a deficiency of dopamine, a chemical that transmits signals between nerve cells. In 1988, when a Hopkins team discovered that the deficiency led certain brain cells to be over-stimulated, not under-stimulated as was previously believed, it became clear that over-active cells could be addressed surgically. In 1997 deep brain stimulation, or DBS, a procedure that had almost disappeared after the introduction of the drug L-dopa around 1965, was approved in the United States for movement disorders.

Now DBS is a standard of care for Parkinson’s, but it also has broad implications for conditions as diverse as obsessive compulsive disorder, obesity and psychiatric disease. Johns Hopkins, with its team of neurosurgeons and fellowship-trained neurologists, is a leading center for DBS in the United States and well positioned to pursue these powerful new treatments.

Fred Lenz evaluates Parkinson’s patient Martha Kowal to see if she is a candidate for deep brain stimulation.

In DBS, a thin insulated wire, or electrode, is inserted through a small opening in the skull and positioned within the targeted brain area, usually, in Parkinson’s patients, the subthalamic nucleus, a tiny mid-brain structure. As with a cardiac pacemaker, an insulated wire is passed under the skin and connects the electrode with a neurostimulator, a battery-run power pack implanted under the skin usually near the collarbone. The generator sends a steady stream of low voltage to the brain, blocking the electrical signals that cause symptoms.

Hopkins neurosurgeon Frederick Lenz was instrumental in reintroducing DBS to neurosurgery after its hiatus. He refined microelectrode recording, an extraordinarily sensitive brain-mapping system which, in DBS, allows surgeons to precisely target specific groups of brain cells.

Lenz and his team have performed more than 400 DBS procedures. “While DBS was once used only in relatively advanced cases of Parkinson’s, we are now taking patients earlier in the course of the disease,” he says.

In Lenz’s hands, involuntary movements improve significantly in 90 percent of patients. Gait improves in 70 to 80 percent. “Almost everyone gets at least a 50 percent reduction in medicine; some can stop taking their drugs completely,” says Lenz. “The risk of infection is 1.5 percent. The risk of a bleed is 1.5 percent. Of that group, less than 1 percent will have a serious hemorrhage. It’s up to the patients to decide whether the problems are significant enough to take the small but present risks of the procedure in order to achieve those results.”

DBS for Depression?
Over the last decade, deep brain stimulation has proven so successful in relieving the symptoms of Parkinson’s disease that clinicians now are casting their eye on other areas that hold promise for this increasingly popular surgical procedure.

DBS has been done experimentally elsewhere on a small number of patients with treatment-resistant depression. The results so far have been promising, and though there has yet to be a definitive randomized study, the concept remains an exciting possibility.

“With movement disorders, we had great preliminary data, we had strong evidence for the target of your procedure, we had the failure of optimal drug therapy,” says neurosurgeon Frederick Lenz, referring to levadopa, the drug many Parkinson’s patients develop a resistance to. “In depression, these lines of evidence are less clear.

“However, neuroscience is advancing at a very rapid pace. I don’t doubt that within a few years implantation of DBS electrodes in patients with psychiatric disease could be the standard of care for depression that is refractory to medical treatment.”