Dystonia in neurodegeneration with brain iron accumulation: outcome of bilateral pallidal stimulation

Pantothenate kinase-associated neurodegeneration (PKAN) and PLA2G6-associated neurodegeneration (PLAN): review of two major neurodegeneration with brain iron accumulation (NBIA) phenotypes

Neurodegeneration with brain iron accumulation (NBIA) comprises a heterogeneous group of disorders characterized by the presence of radiologically discernible high brain iron, particularly within the basal ganglia. A number of childhood NBIA syndromes are described, of which two of the major subtypes are pantothenate kinase-associated neurodegeneration (PKAN) and PLA2G6-associated neurodegeneration (PLAN). PKAN and PLAN are autosomal recessive NBIA disorders due to mutations in PANK2 and PLA2G6, respectively. Presentation is usually in childhood, with features of neurological regression and motor dysfunction. In both PKAN and PLAN, a number of classical and atypical phenotypes are reported. In this chapter, we describe the clinical, radiological, and genetic features of these two disorders and also discuss the pathophysiological mechanisms postulated to play a role in disease pathogenesis.

Genetics and Pathophysiology of Neurodegeneration with Brain Iron Accumulation (NBIA)

Our understanding of the syndromes of Neurodegeneration with Brain Iron Accumulation (NBIA) continues to grow considerably. In addition to the core syndromes of pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2), several other genetic causes have been identified (including FA2H, C19orf12, ATP13A2, CP and FTL). In parallel, the clinical and pathological spectrum has broadened and new age-dependent presentations are being described. There is also growing recognition of overlap between the different NBIA disorders and other diseases including spastic paraplegias, leukodystrophies and neuronal ceroid lipofuscinosis which makes a diagnosis solely based on clinical findings challenging. Autopsy examination of genetically-confirmed cases demonstrates Lewy bodies, neurofibrillary tangles, and other hallmarks of apparently distinct neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease. Until we disentangle the various NBIA genes and their related pathways and move towards pathogenesis-targeted therapies, the treatment remains symptomatic. Our aim here is to provide an overview of historical developments of research into iron metabolism and its relevance in neurodegenerative disorders. We then focus on clinical features and investigational findings in NBIA and summarize therapeutic results reviewing reports of iron chelation therapy and deep brain stimulation. We also discuss genetic and molecular underpinnings of the NBIA syndromes.

Excess iron harms the brain: the syndromes of neurodegeneration with brain iron accumulation (NBIA)

Regulation of iron metabolism is crucial: both iron deficiency and iron overload can cause disease. In recent years, our understanding of the syndromes of Neurodegeneration with Brain Iron Accumulation (NBIA) continues to grow considerably. These are characterized by excessive iron deposition in the brain, mainly the basal ganglia. Pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2) are the core syndromes, but several other genetic causes have been identified (including FA2H, C19orf12, ATP13A2, CP and FTL). These conditions show a wide clinical and pathological spectrum, with clinical overlap between the different NBIA disorders and other diseases including spastic paraplegias, leukodystrophies, and neuronal ceroid lipofuscinosis. Lewy body pathology was confirmed in some clinical subtypes (C19orf12-associated neurodegeneration and PLAN). Research aims at disentangling the various NBIA genes and their related pathways to move towards pathogenesis-targeted therapies. Until then treatment remains symptomatic. Here we will introduce the group of NBIA syndromes and review the main clinical features and investigational findings.

Update on dystonia

PURPOSE OF REVIEW

This review considers the recent literature pertaining to the clinical features, genetics, neuropathology and treatment of dystonia syndromes.

RECENT FINDINGS

The term dystonia indicates at the same time a clinical phenotype and a collection of neurological syndromes mainly of genetic origin. The physical signs contributing to the phenomenology of dystonia have been recently assembled into a coherent set. The molecular genetics of primary dystonia syndromes (DYT1 and DYT6) have been the object of extensive analysis, providing converging views on their causative mechanisms. The relationship between genotype, phenotype, and endophenotypes has been explored for hereditary and sporadic dystonia syndromes. Neurophysiological studies on DYT1 and DYT6 patients, as well as on nonmanifesting carriers, have demonstrated the presence of altered synaptic plasticity. Several recent data indicate a role of dopamine and acetylcholine (ACh) transmission in the pathophysiology of primary dystonia.

SUMMARY

Recent findings have led to novel, testable hypotheses on cellular mechanisms and physiopathological abnormalities underlying dystonia. Neurophysiological studies, imaging data and animal models support the view that corticostriatal, cerebellar, and dopaminergic dysfunctions converge to produce the pathophysiological abnormalities of dystonia.

Surgical treatment for secondary dystonia

Surgical therapy for the secondary dystonias is generally perceived to be less effective than for primary disease. However, a number of case reports and small open series have recently appeared describing quite favorable outcomes following surgery for some nonprimary dystonias. We discuss surgical treatment options for this group of diverse conditions, including tardive dystonia, dystonic cerebral palsy, and certain heredodegenerative diseases in which deep brain stimulation and ablative lesions of the posteroventral pallidum have been shown to be effective. Other types of secondary dystonia respond less well to pallidal surgery, particularly when anatomical lesions of the basal ganglia are prominent on preoperative imaging. For these conditions, central baclofen delivery and botulinum toxin denervation may be considered. With optimal medical and surgical care, some patients with secondary dystonia have achieved reductions in disability and pain that approach those documented for primary dystonia.

Pediatric indications for deep brain stimulation

PURPOSE

Based on the success of deep brain stimulation (DBS) in the treatment of adult disorders, it is reasonable to assume that the application of DBS in the pediatric population is an emerging area worthy of study. The purpose of this paper is to outline the current movement disorder indications for DBS in the pediatric population, and to describe areas of investigation, including possible medically refractory psychiatric indications.

METHODS

We performed a structured review of the English language literature from 1990 to 2011 related to studies of DBS in pediatrics using Medline and PubMed search results.

RESULTS

Twenty-four reports of DBS in the pediatric population were found. Based on published data on the use of DBS for pediatric indications, there is a spectrum of clinical evidence for the use of DBS to treat different disorders. Dystonia, a disease associated with a low rate of remission and significant disability, is routinely treated with DBS and is currently the most promising pediatric application of DBS. We caution the application of DBS to conditions associated with a high remission rate later in adulthood, like obsessive-compulsive disorder and Tourette's syndrome. Moreover, epilepsy and obesity are currently being investigated as indications for DBS in the adult population; however, both are associated with significant morbidity in pediatrics.

CONCLUSION

While currently dystonia is the most promising application of DBS in the pediatric population, multiple conditions currently being investigated in adults also afflict children and adolescents, and thus warrant further research.

Beyond the Burke-Fahn-Marsden Dystonia Rating Scale: deep brain stimulation in childhood secondary dystonia

PURPOSE

Deep brain stimulation is now widely accepted as an effective treatment for children with primary generalized dystonia. More variable results are reported in secondary dystonias and its efficacy in this heterogeneous group has not been fully elucidated. Deep brain stimulation outcomes are typically reported using impairment-focused measures, such as the Burke-Fahn-Marsden Dystonia Rating Scale, which provide little information about function and participation outcomes or changes in non-motor areas. The aim is to demonstrate that in some cases of secondary dystonia, the sole use of impairment level measures, such as the Burke-Fahn-Marsden Dystonia Rating Scale, may be insufficient to fully evaluate outcome following deep brain stimulation.

METHODS

Six paediatric cases who underwent deep brain stimulation surgery with a minimum of one year follow up were selected on the basis of apparent non-response to deep brain stimulation, defined as a clinically insignificant change in the Burke-Fahn-Marsden Dystonia Movement Scale (<20%), but where other evaluation measures demonstrated clinical efficacy across several domains.

RESULTS

Despite no significant change in Burke-Fahn-Marsden Dystonia Rating Scale scores following deep brain stimulation, parallel outcome measures demonstrated significant benefit in a range of child and family-centred goal areas including: pain and comfort, school attendance, seating tolerance, access to assistive technology and in some cases carer burden.

CONCLUSIONS

Sole use of impairment-focused measures, are limited in scope to evaluate outcome following deep brain stimulation, particularly in secondary dystonias. Systematic study of effects across multiple dimensions of disability is needed to determine what deep brain stimulation offers patients in terms of function, participation, care, comfort and quality of life. Deep brain stimulation may offer meaningful change across multiple domains of functioning, disability and health even in the absence of significant change in dystonia rating scales.

Therapeutic advances in neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) includes a heterogeneous group of genetically defined disorders characterized by progressive extrapyramidal deterioration and iron accumulation in the basal ganglia. Current medical options for these disorders remain largely unsatisfactory and do not prevent the disease from progressing to a severe and disabling state. In select cases, surgical techniques, such as deep brain stimulation, may be effective in ameliorating some of the symptoms of the disease. The availability of chelating agents with specific properties that have been demonstrated to be effective in other disorders with regional iron accumulation as well as magnetic resonance imaging techniques that allow for quantitative assessment of iron have stimulated interest in the use of chelating agents in NBIA. This review aims to describe the role of surgical therapies in NBIA, discuss the use of chelating agents in NBIA, and presents new therapeutic approaches under consideration.

Syndromes of neurodegeneration with brain iron accumulation

In parallel to recent developments of genetic techniques, understanding of the syndromes of neurodegeneration with brain iron accumulation has grown considerably. The acknowledged clinical spectrum continues to broaden, with age-dependent presentations being recognized. Postmortem brain examination of genetically confirmed cases has demonstrated Lewy bodies and/or tangles in some forms, bridging the gap to more common neurodegenerative disorders, including Parkinson disease. In this review, the major forms of neurodegeneration with brain iron accumulation (NBIA) are summarized, concentrating on clinical findings and molecular insights. In addition to pantothenate kinase-associated neurodegeneration (PKAN) and phospholipase A2-associated neurodegeneration (PLAN), fatty acid hydroxylase-associated neurodegeneration (FAHN) NBIA, mitochondrial protein-associated neurodegeneration, Kufor-Rakeb disease, aceruloplasminemia, neuroferritinopathy, and SENDA syndrome (static encephalopathy of childhood with neurodegeneration in adulthood) are discussed.

Current concepts and controversies in neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) encompasses at least 7 genetically distinct disorders, and additional causative genes likely await identification. Recent advances have included the characterization of new genes associated with new subtypes of NBIA and also highlighted the phenotypic heterogeneity of this class of disorders. Herein, we summarize current concepts of NBIA pathogenesis and discuss important gaps in current knowledge, outlining key questions in the field.

A new phenotype of brain iron accumulation with dystonia, optic atrophy, and peripheral neuropathy

BACKGROUND

Neurodegeneration with brain iron accumulation is clinically and genetically heterogeneous because of mutations in at least 7 nuclear genes.

METHODS

We performed homozygosity mapping and whole-exome sequencing in 2 brothers with brain iron accumulation from a consanguineous family.

RESULTS

We identified a homozygous missense mutation in both brothers in the very recently identified chromosome 19 open-reading frame 12 gene. The disease presented before age 10 with slowly progressive tremor, dystonia, and spasticity. Additional features were optic atrophy, peripheral neuropathy, and learning difficulties. A raised serum creatine kinase indicated neuromuscular involvement, and compensatory mitochondrial proliferation implicated mitochondrial dysfunction as a pathological mechanism.

CONCLUSIONS

Further studies are needed to explore the function of the chromosome 19 open-reading frame 12 gene, and extended genetic analysis on larger patient cohorts will provide more information about the presentation and frequency of this disease.

Update on pediatric dystonias: etiology, epidemiology, and management

Dystonia is a movement disorder characterized by sustained muscle contractions producing twisting, repetitive, and patterned movements or abnormal postures. Dystonia is among the most commonly observed movement disorders in clinical practice both in adults and children. It is classified on the basis of etiology, age at onset of symptoms, and distribution of affected body regions.

Etiology

The etiology of pediatric dystonia is quite heterogeneous. There are many different genetic syndromes and several causes of symptomatic syndromes. Dystonia can be secondary to virtually any pathological process that affects the motor system, and particularly the basal ganglia.

Classification

The etiological classification distinguishes primary dystonia with no identifiable exogenous cause or evidence of neurodegeneration and secondary syndromes.

Treatment

Treatment for most forms of dystonia is symptomatic and includes drugs (systemic or focal treatments, such as botulinum toxin) and surgical procedures. There are several medications including anticholinergic, dopamine-blocking and depleting agents, baclofen, and benzodiazepines. In patients with dopamine synthesis defects L-dopa treatment may be very useful. Botulinum toxin treatment may be helpful in controlling the most disabling symptoms of segmental or focal dystonia. Long-term electrical stimulation of the globus pallidum internum appears to be especially successful in children suffering from generalized dystonia.

Deep brain stimulation in children: experience and technical pearls

OBJECT

Deep brain stimulation (DBS) is an established technique for the treatment of several movement disorders in adults. However, the technical approach, complications, and results of DBS in children have not been well documented.

METHODS

A database of DBS implantations performed at a single institution, prospectively established in 1998, was reviewed for patients who received DBS prior to the age of 18. Diagnoses, surgical technique, and complications were noted. Outcomes were assessed using standard rating scales of neurological function.

RESULTS

Of 815 patients undergoing DBS implantation over a 12-year period, 31 were children (mean age at surgery 13.2 years old, range 4-17 years old). Diagnoses included the following: DYT1 primary dystonia (autosomal dominant, Tor1AΔGAG mutation, 10 cases), non-DYT1 primary dystonia (3 cases), secondary dystonia (11 cases), neurodegeneration with brain iron accumulation (NBIA, 3 cases), levodopa-responsive parkinsonism (2 cases), Lesch-Nyhan disease (1 case), and glutaric aciduria Type 1 (1 case). Six children ages 15-17 years old underwent awake microelectrode-guided surgery. For 25 children operated under general anesthesia, the surgical technique evolved from microelectrode-guided surgery to image-guided surgeries using real-time intraoperative MR imaging or CT for lead location confirmation. Complications included 5 hardware infections, all in children younger than 10 years old. At 1 year after implantation, patients with DYT1 dystonia had a mean improvement in the Burke-Fahn-Marsden Dystonia Rating Scale movement subscore of 75%, while those with secondary dystonia had only small improvements. Outcomes in the 3 children with NBIA were disappointing.

CONCLUSIONS

Results of DBS in children with primary and secondary dystonias were similar to those in adults, with excellent results for DYT1 dystonia in children without fixed orthopedic deformity and much more modest results in secondary dystonia. In contrast to reported experience in adults with NBIA, these results in children with NBIA were poor. Infection risk was highest in the youngest patients.

Pantothenate kinase-associated neurodegeneration in Korea: recurrent R440P mutation in PANK2 and outcome of deep brain stimulation

BACKGROUND AND PURPOSE

The purpose of this study was to evaluate the mutation status of PANK2 among Korean patients with pantothenate kinase-associated neurodegeneration (PKAN) and to document the outcome of pallidal deep brain stimulation (DBS).

METHODS

Direct sequencing and deletion/duplication analysis of PANK2 were conducted in 12 patients (11 unrelated) with PKAN, diagnosed on the basis of extrapyramidal dysfunction and the 'eye-of-the-tiger sign' on brain magnetic resonance imaging (MRI). Pallidal DBS was conducted in four patients, and the outcomes were measured using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS).

RESULTS

A PANK2 mutation was identified in both alleles in all patients. The most prevalent mutation was c.1319G>C (p.R440P) in 8/22 mutated alleles (36%). An intragenic deletion ranging from exons 2 to 4 was found in one allele (1/22, 4.5%) using deletion/duplication analysis. The outcome of pallidal DBS was favorable in two patients with atypical PKAN and moderate severity of dystonia. However, two patients with typical PKAN and relatively severe symptoms showed variable responses.

CONCLUSIONS

The c.1319G>C (p.R440P) mutation appears to be a founder genotype among Korean patients with PKAN. Furthermore, this study provides additional data for the recent international effort to evaluate the efficacy of pallidal DBS in the treatment of patients with PKAN.

Neuropsychological, neuropsychiatric, and quality of life issues in DBS for dystonia

We review the impact of dystonia and its surgical treatment with deep brain stimulation (DBS) on cognitive function, psychiatric morbidity, and health-related quality of life. The current evidence suggests that globus pallidus internus (GPi) DBS does not cause cognitive decline in primary dystonia. However, we recommend general preoperative screening of cognition in patients with dystonia to evaluate baseline cognitive status and monitor for possible postoperative changes. Patients with mild to moderate depression appear to do well postoperatively; however, there are scant data about those with severe depression. This is particularly problematic given reports of postoperative suicide. Patients with tardive dystonia seem to do well post-GPi DBS despite often having a history of depression or even having active severe depression. We make recommendations for screening and basic management strategies of patients identified as having a major psychiatric illness pre- or postoperatively. Quality of life in dystonia patients quantified by generic measures such as the SF36 showed improvement in both mental and physical categories following DBS surgery.

Deep brain stimulation: current and future clinical applications

Deep brain stimulation (DBS) has developed during the past 20 years as a remarkable treatment option for several different disorders. Advances in technology and surgical techniques have essentially replaced ablative procedures for most of these conditions. Stimulation of the ventralis intermedius nucleus of the thalamus has clearly been shown to markedly improve tremor control in patients with essential tremor and tremor related to Parkinson disease. Symptoms of bradykinesia, tremor, gait disturbance, and rigidity can be significantly improved in patients with Parkinson disease. Because of these improvements, a decrease in medication can be instrumental in reducing the disabling features of dyskinesias in such patients. Primary dystonia has been shown to respond well to DBS of the globus pallidus internus. The success of these procedures has led to application of these techniques to multiple other debilitating conditions such as neuropsychiatric disorders, intractable pain, epilepsy, camptocormia, headache, restless legs syndrome, and Alzheimer disease. The literature analysis was performed using a MEDLINE search from 1980 through 2010 with the term deep brain stimulation, and several double-blind and larger case series were chosen for inclusion in this review. The exact mechanism of DBS is not fully understood. This review summarizes many of the current and potential future clinical applications of this technology.

Childhood disorders of neurodegeneration with brain iron accumulation (NBIA)

Neurodegeneration with brain iron accumulation (NBIA) comprises a heterogeneous group of progressive complex motor disorders characterized by the presence of high brain iron, particularly within the basal ganglia. A number of autosomal recessive NBIA syndromes can present in childhood, most commonly pantothenate kinase-associated neurodegeneration (PKAN; due to mutations in the PANK2 gene) and phospholipase A2 group 6-associated neurodegeneration (PLAN; associated with genetic defects in PLA2G6). Mutations in the genes that cause these two neuroaxonal dystrophies are thought to disrupt the normal cellular functions of phospholipid remodelling and fatty acid metabolism. A significant proportion of children with an NBIA phenotype have no genetic diagnosis and there are, no doubt, additional as yet undiscovered genes that account for a number of these cases. NBIA disorders can be diagnostically challenging as there is often phenotypic overlap between the different disease entities. This review aims to define the clinical, radiological, and genetic features of such disorders, providing the clinician with a stepwise approach to appropriate neurological and genetic investigation, as well as a clinical management strategy for these neurodegenerative syndromes.

Cognitive functioning in children with pantothenate-kinase-associated neurodegeneration undergoing deep brain stimulation

AIM

To examine the cognitive functioning of young people with pantothenate-kinase-associated neurodegeneration (PKAN) after pallidal deep brain stimulation (DBS). PKAN is characterized by progressive generalized dystonia and has historically been associated with cognitive decline. With growing evidence that DBS can improve motor function in adults and children with PKAN, there is now the opportunity to study the cognitive profiles of these patients over time.

METHOD

We present a case series of seven children (mean age 11 y 7 mo, SD 3 y 2 mo) undergoing bilateral pallidal DBS for the management of severe PKAN-associated dystonia. We administered standardized measures of intellectual ability and memory where possible, before DBS and 1 to 4 years after DBS.

RESULTS

No cognitive decline was observed and scores improved in all but one child (whose dystonia could not be adequately controlled owing to multiple medical problems). In line with a stabilization or reduction in their dystonia, all but one child was able to tolerate longer assessment sessions and complete either the same or a greater number of subtests.

INTERPRETATION

These findings suggest that apparent cognitive impairments may reflect difficulties in accessing cognition owing to severity of dystonia. Intellectual decline previously associated with PKAN may have been overestimated.

Deep brain stimulation for hyperkinetics disorders: dystonia, tardive dyskinesia, and tics

PURPOSE OF REVIEW

This review focuses on new insights in deep brain stimulation (DBS) for patients with hyperkinetic movement disorders: dystonia, tardive dyskinesia and Gille de la Tourette's syndrome, during the last 18 months.

RECENT FINDINGS

The recent literature confirms the efficacy of high-frequency stimulation of the globus pallidus internus (GPi) for primary dystonia, generalized or not, with a stable effect over time. The benefit of DBS in other forms of localized dystonia remains to be demonstrated in larger studies. Some clinical and radiological predictive factors have been determined with a predominant influence of the disease duration. Tardive dystonia and myoclonus-dystonia are also improved by GPi stimulation. Encouraging results obtained in cerebral palsy may pave the way for the application of DBS in other secondary dystonia. In Gilles de la Tourette's syndrome, both stimulation of the centre-median/parafascicular nucleus of the thalamus and GPi stimulation (ventromedial) have demonstrated efficacy with stable long-term effect. Thalamic stimulation failed to improve obsessions and compulsions in some patients. Stimulation of the nucleus accumbens has been tested in few cases with contradictory efficacy. In both diseases, complications are rare with no major side effects.

SUMMARY

The few controlled studies showed that bilateral GPi stimulation is a well tolerated and a long-term effective treatment for hyperkinetic disorders. However, recent published data of DBS applied in different targets or patients (especially secondary dystonia) are mainly uncontrolled case reports, precluding the clear determination of the efficacy of this procedure and the choice of the 'good' target for the 'good' patient.

[Deep brain stimulation for treatment of dystonia and tremor]

Deep brain stimulation (DBS) is a safe and successful therapeutic option for patients with dystonia and tremor syndrome who do not respond sufficiently to conservative therapies. The most common target of DBS in patients with dystonia is the internal region of the globus pallidus (GPI). DBS of the GPI leads to long-lasting and remarkable improvement of dystonic movements in about 80% of patients. Recently it could be shown that not only patients with idiopathic dystonia but also patients with secondary dystonia can benefit from DBS although to a somewhat lesser extent. In patients with tremor syndromes, such as essential tremor, tremor-dominant Parkinson's disease or tremor in multiple sclerosis (MS) the intermediate ventral nucleus of the thalamus (VIM) as well as the subthalamic region proved to be promising targets for DBS electrodes. Especially in patients with essential tremor VIM-DBS leads to an often acute reduction of the tremor syndrome. In long-term observations, however, patients with essential tremor showed some tolerability to VIM-DBS leading to a slow increase of stimulation parameters to maintain a stable effect. VIM-DBS in patients with Parkinson's disease is rare and is reserved for elderly patients with pronounced tremor syndrome and little disease progression. Controlled studies and data on DBS in MS tremor are lacking and data are sparse and heterogeneous. Therefore, VIM-DBS in MS tremor patients has to be evaluated individually with caution. In summary patients with tremor syndromes as well as dystonia who cannot be adequately controlled with conservative therapy are good candidates for deep brain stimulation, a therapeutic option with moderate complications and risks and very good outcome for most patients.