Dystonia patients can benefit significantly from brain stimulation. The severity of their symptoms is reduced by more than half, and the effectiveness does not decrease noticeably even after many years.
Stimulating the subthalamic nucleus (mauve) also reduces dystonia. Photo: Medtronic
By Thomas Müller
Over the last two decades, the treatment of patients with dystonia has taken great leaps forward. For example, botulinum toxin has been found to be very effective in the management of focal dystonia. However, pharmacotherapy is more difficult in cases of severe generalised dystonia. Deep brain stimulation (DBS) has now become established in this field, according to Professor Andreas Kupsch of Berlin's Charité teaching hospital. In the first controlled studies, the severity of the symptoms was reduced by around 50 percent.
At the neurology congress in Hamburg Prof. Kupsch presented data from a German placebo-controlled study involving 40 patients with generalised dystonia who had electrodes implanted in their brains for stimulating the pallidum. Here, too, the average reduction in symptoms was 50 percent on a dystonia rating scale. By contrast, patients whose stimulator was left switched off (placebo group) experienced practically no relief. In total around 85 percent of the patients responded well to the stimulation, while the treatment failed in only four patients (ten percent).
If we look at only those patients that responded to DBS, symptoms were reduced by 60 to 70 percent in this group, Kupsch said.
The patients in the study have now been receiving stimulation for an average of three years, and some patients have already been treated successfully for ten years without a drop in the efficacy of the stimulation, Kupsch reported.
Similar success rates were also observed in a small study of ten patients with primary cervical dystonia. DBS alleviated their symptoms by 40 to 50 percent. Kupsch also mentioned success in rare forms of dystonia, such as myoclonus dystonia syndrome, which is caused by a genetic defect. In the ten patients operated on so far, the dystonia symptoms were reduced by up to 80 percent. DBS is also an option in primary Meige's syndrome with uncontrollable symmetrical contractions of the muscles of the face, jaw or throat.
Kupsch presented the case of a woman who could hardly swallow owing to uncontrollable movements of the tongue. Treatment with deep brain stimulation largely normalised this behaviour. The doctors decided to treat this patient with deep brain stimulation because they considered botulinum toxin to be too risky in the tongue. In general, however, the bacterial toxin should be the first treatment considered for focal dystonia, Kupsch said.
It is difficult to predict which patients will benefit from deep brain stimulation, he added. In studies the only criterion for a poor therapeutic outcome in primary dystonia was long duration of the disease. Deep brain stimulation should also be considered for treating severe secondary dystonia, for example in Huntington's disease, but in these patients only a 30 percent reduction of symptoms can be expected. However, this reduction may certainly be clinically relevant.
Dystonia occurs when the control of the involuntary motor activity by the basal ganglia is disrupted. The internal globus pallidus (GPi) evidently plays an important role in the condition. It is therefore the preferred site of stimulation in the treatment of dystonia. A stimulation frequency of 100 Hz has proved effective.