Deep Brain Stimulation of the Globus Pallidus Internus in a Child with Refractory Dystonia due to L2-Hydroxyglutaric Aciduria

INTRODUCTION

L-2-hydroxyglutaric aciduria (L2HGA) is a rare neurometabolic disorder marked by progressive and debilitating psychomotor deficits. Here, we report the first patient with L2HGA-related refractory dystonia that was managed with deep brain stimulation to the bilateral globus pallidus internus (GPi-DBS).

CASE PRESENTATION

We present a 17-year-old female with progressive decline in cognitive function, motor skills, and language ability which significantly impaired activities of daily living. Neurological exam revealed generalized dystonia, significant choreic movements in the upper extremities, slurred speech, bilateral dysmetria, and a wide-based gait. Brisk deep tendon reflexes, clonus, and bilateral Babinski signs were present. Urine 2-OH-glutaric acid level was significantly elevated. Brain MRI showed extensive supratentorial subcortical white matter signal abnormalities predominantly involving the U fibers and bilateral basal ganglia. Genetic testing identified a homozygous pathogenic mutation in the L-2-hydroxyglutarate dehydrogenase gene c. 164G>A (p. Gly55Asp). Following minimal response to pharmacotherapy, GPi-DBS was performed. Significant increases in mobility and decrease in dystonia were observed at 3 weeks, 6 months, and 12 months postoperatively.

CONCLUSION

This is the first utilization of DBS as treatment for L2HGA-related dystonia. The resulting significant improvements indicate that pallidal neuromodulation may be a viable option for pharmaco-resistant cases, and possibly in other secondary metabolic dystonias.

Surgical treatment of movement disorders in neurometabolic conditions

Refractory movement disorders are a common feature of inborn errors of metabolism (IEMs), significantly impacting quality of life and potentially leading to life-threatening complications such as status dystonicus. Surgical techniques, including deep brain stimulation (DBS) and lesioning techniques, represent an additional treatment option. However, the application and benefits of these procedures in neurometabolic conditions is not well understood. This results in challenges selecting surgical candidates and counseling patients preoperatively. In this review, we explore the literature of surgical techniques for the treatment of movement disorders in IEMs. Globus pallidus internus DBS has emerged as a beneficial treatment option for dystonia in Panthotate-Kinase-associated Neurodegeneration. Additionally, several patients with Lesch-Nyhan Disease have shown improvement following pallidal stimulation, with more robust effects on self-injurious behavior than dystonia. Although there are numerous reports describing benefits of DBS for movement disorders in other IEMs, the sample sizes have generally been small, limiting meaningful conclusions. Currently, DBS is preferred to lesioning techniques. However, successful use of pallidotomy and thalamotomy in neurometabolic conditions has been reported and may have a role in selected patients. Surgical techniques have also been used successfully in patients with IEMs to treat status dystonicus. Advancing our knowledge of these treatment options could significantly improve the care for patients with neurometabolic conditions.

Deep Brain Stimulation of the Globus Pallidus Internus for Secondary Dystonia: Clinical Cases and Systematic Review of the Literature Regarding the Effectiveness of Globus Pallidus Internus versus Subthalamic Nucleus

OBJECTIVE

Deep brain stimulation (DBS) is a frequently applied therapy in primary dystonia. For secondary dystonia, the effects can be less favorable. We share our long-term findings in 9 patients with severe secondary dystonia and discuss these findings in the light of the literature.

METHODS

Patients who had undergone globus pallidus internus (GPi)-DBS for secondary dystonia were included. Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) scores, clinical improvement rates, follow-up periods, stimulation parameters and the need for internal pulse generator replacements were analyzed. The PubMed and Google Scholar databases were searched for articles describing GPi-DBS and subthalamic nucleus (STN)-DBS only for secondary dystonia cases. Keywords were "dystonia," "deep brain stimulation," "GPi," "dystonia," "deep brain stimulation," and "STN."

RESULTS

A total of 9 secondary dystonia patients (5 male, 4 female) had undergone GPi-DBS with microelectrode recording in our units. The mean follow-up period was 29 months. The average BFMDRS score was 58.2 before the surgery, whereas the mean value was 36.5 at the last follow-up of the patients (mean improvement, 39%; minimum, 9%; maximum, 63%). In the literature review, we identified 264 GPi-DBS cases (mean follow-up, 19 months) in 72 different articles about secondary dystonia. The mean BFMDRS improvement rate was 52%. In 146 secondary dystonia cases, reported in 19 articles, STN-DBS was performed. The average follow-up period was 20 months and the improvement in BFMDRS score was 66%.

CONCLUSIONS

Although GPi-DBS has favorable long-term efficacy and safety in the treatment of patients with secondary dystonia, STN seems a promising target for stimulation in patients with secondary dystonia. Further studies including a large number of patients, longer follow-up periods, and more homogenous patients are necessary to establish the optimal target for DBS in the management of secondary dystonias.

Deep Brain Stimulation in Rare Inherited Dystonias

BACKGROUND

Rare causes of inherited movement disorders often present with a debilitating phenotype of dystonia, sometimes combined with parkinsonism and other neurological signs. Since these disorders are often resistant to medications, DBS may be considered as a possible treatment.

METHODS

Patients with identified genetic diseases (ataxia-telangiectasia, chorea-achantocytosis, dopa-responsive dystonia, congenital nemaline myopathy, methylmalonic aciduria, neuronal ceroid lipofuscinosis, spinocerebellar ataxia types 2 and 3, Wilson's disease, Woodhouse-Sakati syndrome, methylmalonic aciduria, and X trisomy) and disabling dystonia underwent bilateral GPi DBS (bilateral thalamic Vim nucleus in 1 case). The primary outcome was the difference in the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) between baseline, 1 year and last available follow-up. Preoperative factors such as age at surgery, disease duration at surgery, proportion of life lived with dystonia and severity of dystonia were correlated to the primary outcome.

RESULTS

Eleven patients were operated between February 2003 and December 2013. Age and duration of disease at time of surgery were 30 ± 19 and 12.5 ± 15.7 years, respectively. DBS effects on dystonia severity were variable but overall marginally effective, with a mean improvement of 7.9% (p = 0.39) at 1-year follow-up and 16.7% (p = 0.46) at last follow-up (mean 47.3 ± 19.9 months after surgery). No preoperative factors were identified to predict the surgical outcome.

CONCLUSION

Our findings support the current knowledge that DBS is modestly effective in treating rare inherited dystonias with a combined phenotype. However, the BFMDRS might not be the best tool to measure outcome in these severely affected patients.

Neurometabolic disorders are treatable causes of dystonia

A broad range of rare inherited metabolic disorders can present with dystonia. For clinicians, it is important to recognize dystonic features, but it can be complicated by the mixed and complex clinical picture seen in many neurometabolic patients. Careful phenotyping is the first step towards the diagnosis of the underlying condition and subsequent targeted treatment, further supported by imaging, biochemical diagnostics and the availability of modern diagnostic techniques such as next generation sequencing. As several neurometabolic disorders are treatable causes of dystonia, these should have priority in the diagnostic process. In the symptomatic treatment of dystonia, several therapeutic options are available. Awareness for the occurrence and optimal treatment of dystonia and other movement disorders in neurometabolic conditions is important because these symptoms can have a substantial impact on the quality of life and daily functioning; this effect is not only exerted by the dystonia itself, but also by the frequently associated non-motor features. In this paper, the highlights and key concepts of neurometabolic forms of dystonia are discussed, with a focus on phenomenology, the diagnostic approach, the most important neurometabolic aetiologies, co-occurring non-motor features and therapeutic options.

Childhood dystonias

OPINION STATEMENT

Dystonia is a movement disorder caused by diverse etiologies. Its treatment in children is particularly challenging due to the complexity of the development of the nervous system from birth to young adulthood. The treatment options of childhood dystonia include several oral pharmaceutical agents, botulinum toxin injections, and deep brain stimulation (DBS) therapy. The choice of drug therapy relies on the suspected etiology of the dystonia and the adverse effect profile of the drugs. Dystonic syndromes with known etiologies may require specific interventions, but most dystonias are treated by trying serially a handful of medications starting with those with the best risk/benefit profile. In conjunction to drug therapy, botulinum toxin injections may be used to target a problematic group dystonic muscles. The maximal botulinum toxin dose is limited by the weight of the child, therefore limiting the number of the muscles amenable to such treatment. When drugs and botulinum toxin injections fail to control the child's disabling dystonia, DBS therapy may be offered as a last remedy. Delivering optimal DBS therapy to children with dystonia requires a multidisciplinary team of experienced pediatric neurosurgeons, neurologists, and nurses to select adequate candidates, perform this delicate stereotactic procedure, and optimize DBS delivery. Even in the best hands, the response of childhood dystonia to DBS therapy varies greatly. Future therapy of childhood dystonia will parallel the advancement of knowledge of the pathophysiology of dystonic syndromes and the development of clinical and research tools for their study.

Deep brain stimulation and dantrolene for secondary dystonia in x-linked adrenoleukodystrophy

Deep brain stimulation (DBS) has been used to treat secondary dystonias caused by inborn errors of metabolism with varying degrees of effectiveness. Here we report for the first time the application of DBS as treatment for secondary dystonia in a 22-year-old male with X-linked adrenoleukodystrophy (X-ALD). The disease manifested at age 6 with ADHD, tics, and dystonic gait, and deteriorated to loss of ambulation by age 11, and speech difficulties, seizures, and characteristic adrenal insufficiency by age 16. DBS in the globus pallidus internus was commenced at age 18. However, after 25 months, no improvement in dystonia was observed (Burke-Fahn-Marsden (BFM) scores of 65.5 and 62 and disability scores of 28 and 26, pre- and post-DBS, respectively) and the DBS device was removed. Treatment with dantrolene reduced skeletal muscle tone and improved movement (Global Dystonia Rating Scores from 5 to 1 and BFM score 42). Therefore, we conclude that DBS was a safe but ineffective intervention in our case with long-standing dystonia, whereas treatment of spasticity with dantrolene did improve the movement disorder in this young man with X-ALD.

Deep brain stimulation for dystonia

The few controlled studies that have been carried out have shown that bilateral internal globus pallidum stimulation is a safe and long-term effective treatment for hyperkinetic disorders. However, most recent published data on deep brain stimulation (DBS) for dystonia, applied to different targets and patients, are still mainly from uncontrolled case reports (especially for secondary dystonia). This precludes clear determination of the efficacy of this procedure and the choice of the 'good' target for the 'good' patient. We performed a literature analysis on DBS for dystonia according to the expected outcome. We separated those with good evidence of favourable outcome from those with less predictable outcome. In the former group, we review the main results for primary dystonia (generalised/focal) and highlight recent data on myoclonus-dystonia and tardive dystonia (as they share, with primary dystonia, a marked beneficial effect from pallidal stimulation with good risk/benefit ratio). In the latter group, poor or variable results have been obtained for secondary dystonia (with a focus on heredodegenerative and metabolic disorders). From this overview, the main results and limits for each subgroup of patients that may help in the selection of dystonic patients who will benefit from DBS are discussed.

Deep brain stimulation for dystonia

The few reported controlled studies show that bilateral stimulation of the globus pallidus interna (GPi) is a safe and effective long-term treatment for hyperkinetic disorders. However, the recently published data on deep brain stimulation (DBS) applied to different targets or patients (especially those with secondary dystonia) are mainly uncontrolled case reports, precluding a clear determination of its efficacy, and providing little guidance as to the choice of a "good" target in a "good" patient. This chapter reviews the literature on DBS in primary dystonia, paying particular attention to the risk:benefit ratio in focal and segmental dystonias (cervical dystonia, cranial dystonia) and to the predictive factors for a good outcome. The chapter also highlights recent data on the marked benefits of the technique in myoclonus dystonia (in which pallidal, as opposed to thalamic, stimulation is more effective) and in tardive dystonia-dyskinesia. Although, the decision to treat appears relatively straightforward in patients with primary dystonia, myoclonus-dystonia, and tardive dystonia who have a normal findings on magnetic resonance imaging and normal cognitive function, there are still no reliable tools to help predict the timescale of postoperative benefit. This chapter provides a comprehensive analysis of the use of the treatment in various types of secondary dystonia, with little to moderate benefit in most cases, based on single cases or small series. Beyond the reduction in the severity of dystonia, the global motor and functional outcome is difficult to determine owing to the paucity of adequate evaluation tools. Because of the large interpatient variability, different targets may be effective depending on the symptoms in each individual.