STN confirmed as preferred stimulation target in Parkinson’s

By Eleanor McDermid, Senior medwireNews Reporter

Subthalamic nucleus (STN) stimulation is at worst equivalent and at best superior to globus pallidus pars interna (GPi) stimulation in patients with Parkinson's disease, shows a randomized trial.

The researchers had hypothesized that GPi stimulation would be more effective, because it would produce similar motor improvements to STN stimulation, but with lower rates of cognitive, mood, and behavioral complications.

But they found no difference between the two for the primary outcomes of disability and a composite of cognitive, mood, and behavioral outcomes. Moreover, patients did better on secondary, off-medication outcomes if given STN rather than GPi stimulation.

For off-medication outcomes, "the difference in disability between the two groups is clinically relevant," translating to clear differences in daily activities that patients can undertake, say study author Rob de Bie (Academic Medical Center, Amsterdam, the Netherlands) and team.

Patients spent about 70% of their time in the on-medication phase, they note, which is why the large differences seen in the off-medication phase did not result in a between-group difference for the primary outcome.

The disability primary endpoint was change on the Academic Medical Center Linear Disability Scale (ALDS) at 1 year after surgery, weighted according to time spent on and off medication. During the year after surgery, scores improved by an average of 3.0 among the 65 patients given GPi stimulation and 7.7 in the 63 given STN stimulation, which was not significantly different.

"This study settles a debate that has been going on for almost two decades," say Paul Krack (University Hospital of Grenoble, France) and Marwan Harizc (UCL Institute of Neurology, London, UK) in a commentary accompanying the study in The Lancet Neurology.

They note that the effects of GPi stimulation are reportedly less durable than those of STN, but GPi has remained of interest because of the suppositions that formed the hypothesis of the current study - the Netherlands SubThalamic and Pallidal Stimulation (NSTAPS) study.

The findings of NSTAPS are "reassuring," say Krack and Harizc, because they reconcile evidence-based medicine with "prevailing and accepted practice" for deep-brain stimulation in PD patients.

Patients given STN stimulation had significantly larger improvements in off-medication phase Unified Parkinson's Disease Rating Scale motor scores, at 20.3 versus 11.4 in patients allocated to GPi stimulation, and in ALDS scores, at 20.3 versus 11.8. They also had a significantly larger medication reduction, at a mean levodopa equivalent of 546 versus 208.

Despite the researchers' hypothesis, 58% of patients in the GPi group and 56% of those in the STN group had cognitive, mood, and behavioral complications, which was not a significant difference. Adverse event rates were similar between the groups.

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