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|NI FEATURE: THE EDITORIAL DEBATE IV-- PROS AND CONS
|Year : 2017 | Volume
| Issue : 6 | Page : 1232-1233
Pallidal deep brain stimulation in dystonia
Manmohan Singh, Kanwaljit Garg
Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
|Date of Web Publication||10-Nov-2017|
Dr. Manmohan Singh
Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Singh M, Garg K. Pallidal deep brain stimulation in dystonia. Neurol India 2017;65:1232-3
Dystonia is defined as “a syndrome of sustained muscle contractions, frequently causing twisting and repetitive movements, or abnormal postures” by the Dystonia Medical Research Foundation. It is characterized by involuntary contractions of agonist and antagonist muscle groups, which is usually made worse by voluntary movements. Abnormal contractions between these muscles cause movement in one direction. Jerky movements result from the patient's efforts to correct the posture. Surgical management of dystonia came into clinical practice as medical management was not very effective in treating these disorders.
Dystonias are classified into four major categories: primary (or idiopathic), secondary (or symptomatic), dystonia-plus syndromes and heredo-degenerative disorders, in which dystonia is a prominent feature.
Dystonias respond to medical management poorly except for the dopa-responsive dystonia. Some focal dystonias can be managed with botulinum toxin. This factor led the surgeons to develop various surgical procedures to treat dystonias. The surgical procedures included sectioning of the overactive muscles, peripheral denervation of dystonic muscles and stereotactic lesions in the thalamus and basal ganglia.
Various stereotactic procedures have been used to treat different types of dystonia. Targets tried included various locations within the thalamus, dentate nucleus, globus pallidus internus and subthalamic nucleus. Lesioning was performed in the past, while stimulation procedures (DBS) are being done in the recent times. Thalamic nuclei were the commonest targets of these stereotactic procedures in the past but a variable response was obtained. Currently, pallidotomy/pallidal DBS are being commonly used to treat dystonia. These stereotactic procedures are an integral part of the therapeutic armamentarium and surgery is offered earlier before the patient develops fixed dystonic postures.
Irving Copper started thalamotomies in the 1950s in patients with primary generalized dystonia and performed more than 100 procedures using various targets in the thalamus (ventralis oralis anterior [Voa], ventralis oralis posterior [Vop], ventralis intermedius [Vim], centralis medialis (CM), pulvinar, and portions of the ventralis posterolateralis (VPL) and ventralis posteromedialis (VPM) nuclei. He reported marked improvement in 24.5% and mild-to- moderate improvement in 45.2% of dystonia patients following a thalamotomy after a mean follow-up of 7.9 years. He found that the improvement was more in Jewish patients with a positive family history (presumably patients with a DYT1 [dystonia 1, torsion gene] mutation), in patients with limb symptoms, and in patients between 11 and 16 years of age. However, the improvement obtained after a thalamotomy may deteriorate over time.
Stereotactic pallidotomy resolves levodopa-induced dyskinesias, including dystonic movements in Parkinson's disease patients. There are few procedure related complications, which has led to the use of pallidotomy in dystonia patients. The posteroventral GPi (globus pallidus internus), the current target of choice, was reported as a good target by Laitinen et al. There is a lot of literature available suggesting a good outcome following a GPi pallidotomy.
| » Pallidal Deep Brain Stimulation|| |
DBS is an excellent treatment option in the management of movement disorders. DBS was first used in the treatment of Parkinson's disease. Based on the positive results in Parkinson's disease, high frequency stimulation was used to treat patients suffering from dystonia. High frequency stimulation is safer than making a lesion and to control the side effects; over and above, it is a reversible procedure.
Target localization methods were a source of debate in the past. With the progress made in the imaging modalities like the magnetic resonance imaging (MRI) and its various sequences, stereotactic targeting has improved significantly. The development of stereotactic Atlas More Detailses of the human brain have allowed targeting of invisible targets. Modern MRI imaging provides improved contrast and exquisite neuroanatomical details. It is now possible to visualize the borders of the GPi directly with MRI and the target can be directly identified.
A significant improvement in the motor and disability scores have been reported (range, 40–80%) in primary generalized and segmental dystonia following pallidal DBS.,,,,, One study of 31 patients with primary generalized dystonia showed a greater clinical improvement in children compared with adults (12 adults and 19 children) at a 2-year follow-up. In the same study, the improvement was comparable in patients with and without the DYT1 mutation in both the functional (P = 0.12) and clinical (P = 0.33) scores at a 2-year follow up. Pallidal stimulation has also been used in patients with dystonia-plus syndromes. It has been reported that secondary dystonia does not respond to DBS as compared to primary dystonia. Nevertheless, several reports have shown satisfactory clinical outcomes in patients with secondary dystonia also. In our clinical practice at AIIMS, we have observed that pallidotomy or DBS in secondary dystonia does not yield optimal results.
GPi is identified directly with high resolution MRI imaging; or, it may be located indirectly i.e., the coordinates are calculated by measuring the internal reference to locate the target, for example, the anterior- posterior commissures (AC–PC line) measured on MRI. Distances are then deduced using a human brain atlas, hypothesizing that the proportions given in the atlas are applicable to all individuals in whom the procedure is undertaken. However, there are substantial individual variations in the coordinates of subcortical nuclei that are based on the AC–PC line. Intraoperative clinical and electrophysiological monitoring with the patient under local anesthesia is done to overcome these inter-individual variations. Microelectrode recording (MER) is also used to identify the target intra-operatively and to validate the target coordinates. Stereotactic targeting of GPi is kept 2 mm superior to the optic tract and at the junction of anterior 2/3rd and posterior 1/3rd of GPi. We keep the target 2 mm anterior to the mid AC-PC point. Bilateral DBS in the same sitting is done in patient with generalized dystonia. Electrodes are implanted along the planned trajectory on either side. Following lead placement, pulse generator is implanted on the same day. Programming is started after 24 to 48 hours of surgery.
Many patients with generalized dystonia show improvement early after DBS surgery but optimal response is seen after 3-5 months. Pallidal DBS is certainly one of the best ways to treat dystonias with excellent long term results with rare side effects. It does not result in a permanent brain lesion and is reversible. The current drawback of DBS is the cost incurred in the procedure which prohibits its use in all patients in our country; in these situations, pallidotomy may be a viable alternative.
| » References|| |
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