Pallidal Stimulation in Primary Dystonia Patients
Pallidal Stimulation in Primary Dystonia Patients
Abstract & Commentary
By Panida Piboolnurak, MD Assistant Professor, Department of Neurology and Neuroscience, Weill Medical College, Cornell University. Dr. Piboolnurak reports no financial relationship relevant to this field of study.
Synopsis: A patient with primary, medically refractory dystonia, without a fixed skeletal deformity is a good candidate for pallidal deep brain stimulation. Shorter disease duration predicts a good outcome, but age of dystonia onset, severity of the disease, DYT1 status, and phasic/tonic predominance do not provide predictive value.
Source: Isaias IU, Alterman RL, Tagliati M. Outcome predictors of pallidal stimulation in patients with primary dystonia: the role of disease duration. Brain 2008;131:1895-1902.
Although deep brain stimulation of the internal globus pallidus (GPi-DBS) is an effective treatment for patients with primary dystonia, there is no well defined outcome predictor of this treatment. To determine the predictors of the response to GPi-DBS, Isaias and colleagues retrospectively reviewed the DBS outcomes in 35 patients with early-onset dystonia (26 years old). Twenty-five patients had DYT1 gene mutation. Seven patients had fixed skeletal deformity.
The severity of dystonia was evaluated before the surgery and 3 and 12 months after the surgery using Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). Dystonia patients with fixed skeletal deformity had a significantly poorer outcome at 12 months due to the poor resolution of limb and axial symptoms. For this reason, the authors excluded this subgroup of patients from further outcome analysis.
Patients older than age 21 years at surgery (n=17) improved 38% less than patients younger than 21 years (n=15) at 3 months after surgery, and 15% less at 1 year. Patients with disease duration longer than 15 years (n=12) improved 49% less than those with shorter disease duration (n=20) at 3 months, and 13% less at 1 year. Because disease duration and age at the surgery were related, the authors used multiple regression analysis to identify which factor had a stronger predictive value and found that disease duration was the only independent variable correlated with DBS outcome.
Patients with DYT1 gene mutation (n=22) were younger at symptom onset and younger at surgery than those without DYT1 gene mutation. They exhibited a greater BFMDRS percentage improvement at 3 months and 1 year. However, when patients were stratified by disease duration, this difference was lost. Disease severity and phasic/tonic predominance of dystonia symptoms did not predict response to DBS.
Of 26 patients who were taking medications before surgery, 9 patients had completely discontinued medications at one year. Concerning DBS parameters, at 3 months, mean voltage was 2.8 V, mean pulse width was 217.2 µsec, and mean frequency was 82.7 Hz. At 12 months, mean voltage was 3.0 V, mean pulse width was 226.6 µsec, and mean frequency was 76.9 Hz. Monopolar stimulation was predominantly used.
Commentary
Dystonia is a movement disorder that causes abnormal sustained posture or involuntary movement. Primary dystonia is not caused by another underlying disease, such as hypoxic brain injury. There are genetic forms and forms without a known cause. Medical treatments include anticholinergics, GABAergic drugs, and botulinum toxin injections. A surgical treatment (GPi-DBS) is generally considered in a refractory case.
This study has confirmed that GPi-DBS is an effective treatment for primary dystonia. It also has shown that disease duration longer than 15 years strongly predicts less satisfactory outcome of GPi-DBS, possibly because the complete resolution of dystonia is more difficult as the aberrant plasticity in dystonia becomes more severe after longer duration of disease. This suggests that GPi-DBS should be considered as soon as medical treatments fail to relieve dystonia and before a patient develops a fixed skeletal deformity.
A patient with primary, medically refractory dystonia, without a fixed skeletal deformity is a good candidate for pallidal deep brain stimulation. Shorter disease duration predicts a good outcome, but age of dystonia onset, severity of the disease, DYT1 status, and phasic/tonic predominance do not provide predictive value.Subscribe Now for Access
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