Consensus emerges about how best to apply this investigational technique.
It is sometimes described as a pacemaker for the brain. Yet deep brain stimulation (DBS) is not yet ready for widespread use. Unlike cardiac pacemakers, DBS does not have an established track record of success or clear guidelines for its use.
The research on DBS is at a much earlier stage — known in the research literature as "proof of principle." Although small preliminary studies suggest that DBS appears safe and may be effective for some patients, questions remain about its applicability and long-term effects.
In DBS, a surgeon implants electrodes in the brain and connects them to a small electrical generator in the chest. DBS uses electricity to modulate the transmission of brain signals in particular areas of the brain, although exactly how it does so remains unknown.
Most psychiatric research on DBS has focused on its use in patients with treatment-resistant major depression or obsessive-compulsive disorder (OCD). And although the early results are promising, they are based on findings from only a small number of patients. Published results are available for 46 patients with depression. About 100 patients with OCD have undergone DBS, but only some of the results have been published.
But the early state of the science hasn't stopped patients from wondering whether DBS is a reasonable treatment option, especially when other approaches haven't provided sufficient symptom relief. Recognizing this, the National Institutes of Health and the Dana Foundation convened an international group of experts, who published a detailed set of recommendations for when DBS should be considered and what challenges remain. In addition, some of the leading researchers in the field have published their own advice in separate papers.
Chief among the concerns: how to ensure selection of appropriate patients, better define targets, and ensure adequate patient care both before and after placement of a DBS device.
Patients with depression can access DBS only through research studies. The FDA has approved a humanitarian device exemption for DBS to treat OCD, which means that institutions are allowed to use it outside the research setting, as long as their institutional review board approves.
Most experts advise that DBS be offered only to patients with treatment-resistant OCD or major depression who have exhausted all other options — such as psychotherapy, medication, and electroconvulsive therapy. Symptoms must be severe and incapacitating, as measured by standard clinical instruments such as the Yale-Brown Obsessive Compulsive Scale or the Beck Depression Inventory.
The consensus panel recommended that DBS be offered only at institutions with an independently reviewed research protocol. In addition, the institutions should have in place a multidisciplinary team that includes, at a minimum, experienced neurosurgeons and neurologists, psychiatrists, psychologists, and case managers. Patients should expect a preoperative assessment that may take at least six to eight weeks, to allow time to determine how severe and untreatable symptoms are.
All of the research so far has been done on adults. Because nothing is yet known about how DBS affects the developing brain or nervous system, children and adolescents are excluded from these trials.
A moving target
In studies of both OCD and major depression, DBS researchers have evaluated several different brain targets. Additional research is necessary to determine which targets are best. Further complicating matters, brain circuitry can develop in slightly different ways, so that the targets need to be individualized for each patient.
Another unknown is how much electrical stimulation to provide. DBS stimulation parameters were originally developed based on earlier research in Parkinson's disease, and then adjusted to alleviate OCD or depression symptoms. But researchers are still trying to refine those parameters.
Risks and challenges
One of the attractions of DBS as a therapy is that the procedure is both adjustable and reversible — unlike other neurosurgical techniques, such as anterior capsulotomy or cingulotomy, which permanently disrupt brain circuits presumed to be dysfunctional. Theoretically, if patients do not like the effects of DBS, they can stop treatment and have the device removed.
But DBS still has significant risks. Implantation of the stimulant device involves boring small holes into the skull and surgery on the chest, with risks such as infection and bleeding, that accompany any surgery.
When batteries run out, the implanted device stops working, and anecdotal reports indicate this may happen without warning. Symptoms may return quickly, causing rapid mood deterioration or behavior changes. Leads and extension wires can also break. Surgery is necessary to replace the batteries or wires.
Finally, little is known about long-term risks of DBS. The first patients with OCD who were treated with DBS have been followed since about 2000; patients with depression have been followed since about 2005.
Postoperative monitoring of patients treated with DBS is ongoing, to allow for adjustment of the stimulation device as well as medication levels and additional therapy. One review noted that DBS requires a lifetime commitment, by both patient and clinician, to maintaining the device and monitoring symptoms.
Patients require intensive support as they recover. The necessity of remaining in close contact with the treatment team may affect not only a patient's day-to-day life, but also long-term life choices such as whether to move to a new location.
In spite of these cautions, however, the researchers involved in DBS studies point to the positive outcomes in patients previously considered treatment resistant. It has brought improvement to 30% to 70% of those with OCD and 35% to 60% of those treated for depression. The next step is to conduct the "gold" standard of studies: randomized, double-blind placebo-controlled trials. Only then will it be possible to determine whether this is a technique that might benefit more people.
Hamani C, et al. "Deep Brain Stimulation of the Subcallosal Cingulate Gyrus for Depression: Anatomical Location of Active Contacts in Clinical Responders and a Suggested Guideline for Targeting," Journal of Neurosurgery (May 29, 2009): Electronic publication ahead of print.
Rabins P, et al. "Scientific and Ethical Issues Related to Deep Brain Stimulation for Disorders of Mood, Behavior, and Thought," Archives of General Psychiatry (Sept. 2009): Vol. 66, No. 9, pp. 931–37.
Read CN, et al. "Psychiatric Neurosurgery 2009: Review and Perspective," Seminars in Neurology (July 2009): Vol. 29, No. 3, pp. 256–65.
For more references, please see www.health.harvard.edu/mentalextra.