4 June 2010. Deep-brain stimulation looks to become popular for a number of neurological and psychological disorders, even as some of the scientific evidence remains scattered and spotty. In psychiatric applications, in particular, many papers report on only a single case study. Scientists have debated the best way to glean accurate information from such limited reports in the commentary pages of the Journal of the American Medical Association over the past few months. A dose of good news came this week on the neurodegeneration side, when researchers reported in the New England Journal of Medicine that either of two potential stimulation sites for Parkinson disease works equally well.

The Threat of Single-Case Reports
Researchers and surgeons are trying DBS for conditions such as obsessive-compulsive disorder and depression (see Part 3). However, the relevant literature includes many single-case reports, said Thomas Schlaepfer of the University Hospital in Bonn, Germany. In addition, some reports highlight secondary outcomes even when the primary outcome is not achieved (e.g., Hamani et al., 2008). Schlaepfer’s concern is that when the outcome is not related to the original goal, the study is not properly controlled and subjects might have other conditions that skew results. “There is a danger that the field might be damaged by these kinds of reports,” Schlaepfer told ARF. Single case studies could prompt doctors to use treatments that remain unproven in controlled clinical studies. And since negative results generally go unreported, it might take a few years for the field to realize that a particular treatment simply does not work.

Schlaepfer, along with Joseph Fins of the Weill Cornell Medical College in New York contributed a commentary to the February 24 JAMA suggesting that this publication bias could lead scientists and doctors in the wrong direction. When researchers publish uncontrolled single-case studies, and journals accept them, journalists naturally cover the results and readers develop hopes that may be unrealistic, Schlaepfer said. “This overhyping of DBS is dangerous,” Schlaepfer said, because it could lead to unethical trials where people receive therapy that is unlikely to work or may cause unexpected side effects.

In the June 2 JAMA, Dieneke Hubbeling of the South West London and St. George’s Mental Health Trust in the UK responded with a letter to the editor noting that single-case reports have plenty of value. “Serendipitous case studies have been important in the history of medicine, for example, in the discovery of penicillin,” Hubbeling noted in the letter. Hubbeling suggested that for studies with a single subject, researchers could shore up their conclusions by comparing the on- and off-stimulation state, switching between the two without telling the DBS recipient which is which. In this “n-of-1 sham-controlled” design, an increase in symptoms with the removal of the stimulation would be at least some evidence for cause and effect, Hubbeling wrote.

Schlaepfer and Fins, in a response to Hubbeling’s letter, asserted that single-case studies should lead to a full-scale clinical trial. “Anything less deprives society of the potential benefits of scientific inquiry and is exploitative of participants because it places them in less-than-fully-powered clinical trials,” they wrote. As a solution, in their original commentary Fins and Schlaepfer called for a registry, similar to the National Institutes of Health’s ClinicalTrials.gov, in which all single-case studies would enter their results and side effects—positive or negative. In fact, Schlaepfer said, it would be easy and inexpensive to piggyback such a registry onto the system NIH already has in place. “It would be a no-brainer to add DBS research and trials,” he told ARF. At present, there is no system in place to encourage and record reporting of single-case and negative results.

STN Versus GPi: It’s a Tie
In the Parkinson’s field, where DBS has its roots, scientists have long wondered whether the subthalamic nucleus (STN) or globus pallidus internal segment (GPi) is the better target to subdue motor symptoms. Researchers with the Veterans Affairs Cooperative Studies Program 468 study, a multicenter group, report their answer in the June 3 New England Journal of Medicine. They performed DBS on 299 people with Parkinson disease, half receiving STN stimulation and half receiving signals targeted to the GPi. This continuing study has already shown DBS works better than medical treatment (see ARF related news story on Weaver et al., 2009).

Overall, the STN and GPi groups gained the same relief of motor symptoms. People with STN stimulation lost a bit of speed in processing and acting on visual information. They also experienced a slight worsening of depression, while GPi subjects enjoyed mildly improved mood. On the plus side for STN recipients, they were more likely to be able to reduce their medication. Overall, quality of life was comparable for both groups, the authors write, and doctors and patients can choose the appropriate target based on non-motor considerations such as medication levels.—Amber Dance.

References:
Follett KA, Weaver FM, Stern M, Hur K, Harris CL, Luo P, Marks WJ, Rothlind J, Sagher O, Moy C, Pahwa R, Burchiel K, Hogarth P, Lai EC, Duda JE, Holloway K, Samii A, Horn S, Bronstein JM, Stoner G, Starr PA, Simpson R, Baltuch G, De Salles A, Huang GD, Reda DJ, CSP 468 Study Group. Pallidal versus subthalamic deep-brain stimulation for Parkinson's disease. N Engl J Med. 2010 Jun 3;362(22):2077-91. Abstract

Hubbeling D. Registering findings from deep brain stimulation. JAMA. 2010 Jun 2;303(21):2139-40. Abstract

Schlaepfer TE, Fins JJ. Deep brain stimulation and the neuroethics of responsible publishing: when one is not enough. JAMA. 2010 Feb 24;303(8):775-6. Abstract

This is the epilogue to a four-part series on DBS. See Part 1, Part 2, Part 3, and Part 4.