Response to levodopa treatment in dopa-responsive dystonia

Neurophysiological assessment of juvenile parkinsonism due to primary monoamine neurotransmitter disorders

No studies have investigated voluntary movement abnormalities and their neurophysiological correlates in patients with parkinsonism due to inherited primary monoamine neurotransmitter (NT) disorders. Nine NT disorders patients and 16 healthy controls (HCs) were enrolled. Objective measurements of repetitive finger tapping were obtained using a motion analysis system. Primary motor cortex (M1) excitability was assessed by recording the input/output (I/O) curve of motor-evoked potentials (MEP) and using a conditioning test paradigm for short-interval intracortical inhibition (SICI) assessment. M1 plasticity-like mechanisms were indexed according to MEPs amplitude changes after the paired associative stimulation protocol. Patient values were considered abnormal if they were greater or lower than two standard deviations from the average HCs value. Patients with aromatic amino acid decarboxylase, tyrosine hydroxylase, and 6-pyruvoyl-tetrahydropterin synthase defects showed markedly reduced velocity (5/5 patients), reduced movement amplitude, and irregular rhythm (4/5 patients). Conversely, only 1 out of 3 patients with autosomal-dominant GTPCH deficiency showed abnormal movement parameters. Interestingly, none of the patients had a progressive reduction in movement amplitude or velocity during the tapping sequence (no sequence effect). Reduced SICI was the most prominent neurophysiological abnormality in patients (5/9 patients). Finally, the I/O curve slope correlated with movement velocity and rhythm in patients. We provided an objective assessment of finger tapping abnormalities in monoamine NT disorders. We also demonstrated M1 excitability changes possibly related to alterations in motor execution. Our results may contribute to a better understanding of the pathophysiology of juvenile parkinsonism due to dopamine deficiency.

Recognizing Atypical Dopa-Responsive Dystonia and Its Mimics

Purpose of Review

Dopa-responsive dystonia (DRD) encompasses a group of phenotypically and genetically heterogeneous neurochemical disorders. Classic GTP cyclohydrolase 1 (GCH-1)-associated DRD consists of early-onset lower limb asymmetrical dystonia, with sleep benefit, diurnal variation, and excellent and sustained response to low l-dopa doses.

Recent Findings

Unlike the classic phenotype, GCH-1-associated DRD may include features inconsistent with the original phenotype. We describe a GCH-1-associated late-onset DRD case with a family history of parkinsonism and cervical dystonia whose response to levodopa was poor and complicated with dyskinesia, blepharospasm, and severe nonmotor symptoms. We use this case as a springboard to review the spectrum of atypical DRD, DRD-plus, and DRD mimics.

Summary

GCH-1-related dystonia may exhibit wide intrafamilial phenotypic variability, no diurnal fluctuation, poor response to l-dopa, and such complications as dyskinesia, epilepsy, sleep disorders, autonomic dysfunction, oculogyric crisis, myoclonus, or tics. More recently, rare GCH-1 variants have been found to be associated with Parkinson disease. Clinicians should be aware of atypical DRD, DRD-plus, and DRD mimics.

A Low Clozapine Dose Improved Refractory Tardive Dystonia without Exacerbating Psychiatric Symptoms: A Case Report

Clozapine is recommended for patients with schizophrenia and tardive dystonia (TD); however, the appropriate dose remains unclear. In this case, a low dose (150 mg/day) of clozapine improved refractory TD and further ameliorated psychiatric symptoms. Herein, we report on a 41-year-old female with schizophrenia and TD who was treated with a low clozapine dose. After eight weeks of continuous clozapine at 150 mg/day (16 weeks after clozapine initiation), her TD dramatically improved, and her psychiatric symptoms were relieved. Low clozapine doses could ameliorate refractory TD. However, this effect might require up to several weeks. Clinicians should be patient unless they consider it better to increase the clozapine dose.

Generalized Dystonia Treated With Deep Brain Stimulator: An Institutional Single Surgeon Experience

Introduction

Dystonia can cause severe disability when left untreated. Once a patient has exhausted medical management, surgical intervention may be the only treatment option. Although not curative, deep brain stimulation has been shown to be beneficial for patients affected by this condition. Our study sought to review patients undergoing deep brain stimulation for medically refractory dystonia to assess outcomes.

Methods

Our institution's operative database was reviewed retrospectively for all patients undergoing deep brain stimulator placement over the last six years. These medical records were reviewed for the severity of dystonia preoperatively and followed postoperatively for 24 months, focusing on the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). Patients with less than two-year postoperative follow-up were excluded from the study. The patients were further stratified by age into Group A, consisting of patients less than 40 years old, and Group B, patients greater than or equal to 40 years old. Other attributes such as age, sex, age of disease onset, disease duration at the time of surgery, genetic tests for dystonia-related genes, and any complication associated with surgery were also reviewed.

Results

Four hundred fifty-five operative cases for deep brain stimulator placement were reviewed, and 16 patients met inclusion criteria for the study. The mean age for our patient cohort was 43.75 years, with four males and 12 females. The average time from the age of disease onset to time of surgery was 9.7 years for Group A and 10.8 years for Group B; the overall average was 10.3 years. All patients had globus pallidus interna (GPi) as their surgical target. The first incidence of a statistically significant decrease in BFMDRS score was noted at three months postoperatively (p<0.001) when compared to preoperative values. Fourteen patients in our cohort underwent preoperative genetic testing for DYT gene mutations, out of which four were found to have a mutation.

Conclusion

Our review of outcomes for primary generalized dystonia at our institution found that deep brain stimulator targeting the GPi is safe and effective. We found an overall 88% response rate with younger patients (< 40-year-old) showing a better response at two years than older patients.

The Human Experience with Intravenous Levodopa

Objective: To compile a comprehensive summary of published human experience with levodopa given intravenously, with a focus on information required by regulatory agencies.

Background: While safe intravenous (IV) use of levodopa has been documented for over 50 years, regulatory supervision for pharmaceuticals given by a route other than that approved by the U.S. Food and Drug Administration (FDA) has become increasingly cautious. If delivering a drug by an alternate route raises the risk of adverse events, an investigational new drug (IND) application is required, including a comprehensive review of toxicity data.

Methods: Over 200 articles referring to IV levodopa were examined for details of administration, pharmacokinetics, benefit, and side effects.

Results: We identified 142 original reports describing IVLD use in humans, beginning with psychiatric research in 1959–1960 before the development of peripheral decarboxylase inhibitors. At least 2760 subjects have received IV levodopa, and reported outcomes include parkinsonian signs, sleep variables, hormone levels, hemodynamics, CSF amino acid composition, regional cerebral blood flow, cognition, perception and complex behavior. Mean pharmacokinetic variables were summarized for 49 healthy subjects and 190 with Parkinson's disease. Side effects were those expected from clinical experience with oral levodopa and dopamine agonists. No articles reported deaths or induction of psychosis.

Conclusion: At least 2760 patients have received IV levodopa with a safety profile comparable to that seen with oral administration.

The genetics of the dystonias--a review based on the new classification of the dystonias

The definition and classification of the dystonias was recently revisited. In the new 2013 classification, the dystonias are subdivided in terms of their etiology according to whether they are the result of pathological changes or structural damage, have acquired causes or are inherited. As hereditary dystonias are clinically and genetically heterogeneous, we sought to classify them according to the new recently defined criteria. We observed that although the new classification is still the subject of much debate and controversy, it is easy to use in a logical and objective manner with the inherited dystonias. With the discovery of new genes, however, it remains to be seen whether the new classification will continue to be effective.

The modern pre-levodopa era of Parkinson's disease: insights into motor complications from sub-Saharan Africa

Delaying the initiation of levodopa has been proposed to reduce the risk of motor complications in Parkinson’s disease. In a 4-year multicentre study in Ghana, Cilia et al. find that motor fluctuations and dyskinesias are predicted by disease duration and levodopa dose, but not by the duration of levodopa therapy.

During the past decade, a number of large drug trials suggested that the initiation of levodopa therapy should be delayed to reduce the risk of motor complications in patients with Parkinson’s disease. However, the relative contribution of the cumulative exposure to levodopa and of disease progression to the pathophysiology of motor fluctuations and dyskinesias is still poorly understood. In this 4-year multicentre study, we investigated a large cohort of patients with Parkinson’s disease in a sub-Saharan African country (Ghana), where access to medication is limited and the initiation of levodopa therapy often occurs many years after onset. The primary objective was to investigate whether the occurrence of motor complications is primarily related to the duration of levodopa therapy or to disease-related factors. Study design included a cross-sectional case-control analysis of data collected between December 2008 and November 2012, and a prospective study of patients followed-up for at least 6 months after the initiation of levodopa therapy. Ninety-one patients fulfilled criteria for clinical diagnosis of idiopathic Parkinson’s disease (58 males, mean age at onset 60.6 ± 11.3 years). Demographic data were compared to those of 2282 consecutive Italian patients recruited during the same period, whereas nested matched subgroups were used to compare clinical variables. Demographic features, frequency and severity of motor and non-motor symptoms were comparable between the two populations, with the only exception of more frequent tremor-dominant presentation in Ghana. At baseline, the proportion of Ghanaian patients with motor fluctuations and dyskinesias was 56% and 14%, respectively. Although levodopa therapy was introduced later in Ghana (mean disease duration 4.2 ± 2.8 versus 2.4 ± 2.1 years, P < 0.001), disease duration at the occurrence of motor fluctuations and dyskinesias was similar in the two populations. In multivariate analysis, disease duration and levodopa daily dose (mg/kg of body weight) were associated with motor complications, while the disease duration at the initiation of levodopa was not. Prospective follow-up for a mean of 2.6 ± 1.3 years of a subgroup of 21 patients who were drug-naïve at baseline [median disease duration 4.5 (interquartile range, 2.3–5) years] revealed that the median time to development of motor fluctuations and dyskinesias after initiation of levodopa therapy was 6 months. We conclude that motor fluctuations and dyskinesias are not associated with the duration of levodopa therapy, but rather with longer disease duration and higher levodopa daily dose. Hence, the practice to withhold levodopa therapy with the objective of delaying the occurrence of motor complications is not justified.

Diagnosis of primary task-specific lower extremity dystonia in a runner

STUDY DESIGN

Resident's case problem.

BACKGROUND

A 56-year-old man was referred to physical therapy for analysis of unusual gait, first noticed 3 years previously when running. Prior to this evaluation, the patient had seen multiple orthopaedic, sports medicine, and neurological specialists while undergoing repeated and extensive testing. Ten months of testing and treatment, including conservative and surgical management, did not provide an explanation for the gait abnormality or result in improvement of the patient's condition.

DIAGNOSIS

The patient's physical examination was relatively unremarkable, considering the severity of the gait abnormality. Distinct abnormalities were apparent with computerized gait analysis and dynamic electromyography, and, when combined with the physical examination findings, led to a suspicion of the task-specific disorder of runner's dystonia. The patient was referred to a neurologist specializing in movement-related disorders, with a final confirmed diagnosis of primary task-specific dystonia with first onset during running (ie, runner's dystonia).

DISCUSSION

Idiopathic, task-specific dystonia of the lower extremity is documented as a very rare occurrence, yet increasing trends in running participation may result in a higher incidence of this condition. Improved awareness of runner's dystonia in the present case might have enhanced the clinical decision-making process and resulted in more timely and effective treatment solutions. Clinical examination findings, including computerized gait analysis and electromyography, in conjunction with imaging, blood, and genetic testing, can aid in the diagnosis of runner's dystonia.

LEVEL OF EVIDENCE

Differential diagnosis, level 4.

Serotonin transporter inhibition attenuates l-DOPA-induced dyskinesia without compromising l-DOPA efficacy in hemi-parkinsonian rats

Long-term dopamine replacement therapy with l-DOPA in Parkinson's disease often leads to the development of abnormal involuntary movements known as l-DOPA-induced dyskinesia. Growing evidence suggests that, following dopamine cell loss, serotonin neurons acting as surrogates for dopaminergic processes take up l-DOPA, convert it to dopamine and release it in an unregulated fashion that precipitates dyskinesia. Although most studies have focused on serotonin 5-HT(1) receptor stimulation as an antidyskinetic strategy, targeting the serotonin transporter modulation of dopamine activity has been overlooked. Therefore, in the current study, selective serotonin reuptake inhibitors were tested for their ability to reduce l-DOPA- and apomorphine-induced dyskinesia. In Experiments 1 and 2, hemi-parkinsonian rats were primed with l-DOPA until stable dyskinesia developed. Rats in Experiment 1 were administered the selective serotonin reuptake inhibitors paroxetine, citalopram or fluoxetine, followed by l-DOPA. Abnormal involuntary movements and forepaw adjusting steps were recorded to determine the effects of these compounds on dyskinesia and motor performance, respectively. Brains were collected on the final test day, after which striatal and raphe monoamines were examined via high-performance liquid chromatography. In Experiment 2, dyskinesias were measured after selective serotonin reuptake inhibitors and apomorphine. Serotonin reuptake inhibitors dose-dependently attenuated l-DOPA- but not apomorphine-induced dyskinesia, and preserved l-DOPA efficacy. Neurochemically, serotonin transporter inhibition enhanced striatal and raphe serotonin levels and reduced its turnover, indicating a potential mechanism of action. The present results support targeting serotonin transporters to improve Parkinson's disease treatment and provide further evidence for the role of the serotonin system in l-DOPA's effects.

Current and future medical treatment in primary dystonia

Dystonia is a hyperkinetic movement disorder, characterized by involuntary and sustained contractions of opposing muscles causing twisting movements and abnormal postures. It is often a disabling disorder that has a significant impact on physical and psychosocial wellbeing. The medical therapeutic armamentarium used in practice is quite extensive, but for many of these interventions formal proof of efficacy is lacking. Exceptions are the use of botulinum toxin in patients with cervical dystonia, some forms of cranial dystonia (in particular, blepharospasm) and writer's cramp; deep brain stimulation of the pallidum in generalized and segmental dystonia; and high-dose trihexyphenidyl in young patients with segmental and generalized dystonia. In order to move this field forward, we not only need better trials that examine the effect of current treatment interventions, but also a further understanding of the pathophysiology of dystonia as a first step to design and test new therapies that are targeted at the underlying biologic and neurophysiologic mechanisms.

Contribution of pre-synaptic mechanisms to L-DOPA-induced dyskinesia

Positron emission tomography (PET) imaging studies have shown that peak-dose dyskinesia is associated to abnormally high levels of synaptic dopamine (DA) in the caudate-putamen of dyskinetic L-DOPA-treated patients. High striatal extracellular DA levels have also been found in dyskinetic 6-OHDA-lesioned rats as compared to non-dyskinetic ones, suggesting that extracellular DA levels may play a key role in the induction of dyskinesia. In this article we review the evidences pointing to the serotonin system as the primary cause for the abnormally high levels of L-DOPA-derived extracellular DA in Parkinson's disease, and we discuss the feasibility of a therapeutic approach targeting this system.

Early-onset primary dystonia

"Dystonia" is the term used to describe abnormal movements consisting of sustained muscle contractions frequently causing twisting and repetitive movements or abnormal postures. Dystonia is classified partly by age at onset because this helps guide the diagnostic work-up and treatment decisions. This chapter focuses on early-onset (<26 years old) primary dystonia. The history, clinical features, genetics, pathophysiology, diagnosis, and treatment of early-onset primary dystonia are discussed. Special emphasis is placed on DYT1 dystonia, the most common, autosomal-dominant, early-onset, primary dystonia. A diagnostic algorithm is proposed for gene-negative early-onset dystonia, and treatment recommendations for generalized, early-onset dystonia are made.

Presynaptic dopaminergic compartment determines the susceptibility to L-DOPA-induced dyskinesia in rats

Drug-induced dyskinesias in dopamine-denervated animals are known to depend on both pre- and postsynaptic changes of the nigrostriatal circuitry. In lesion models used thus far, changes occur in both of these compartments and, therefore, it has not been possible to dissect the individual contribution of each compartment in the pathophysiology of dyskinesias. Here we silenced the nigrostriatal dopamine neurotransmission without affecting the anatomical integrity of the presynaptic terminals using a short-hairpin RNA-mediated knockdown of tyrosine hydroxylase enzyme (shTH). This treatment resulted in significant reduction (by about 70%) in extracellular dopamine concentration in the striatum as measured by on-line microdialysis. Under these conditions, the animals remained nondyskinetic after chronic L-DOPA treatment, whereas partial intrastriatal 6-hydoxydopamine lesioned rats with comparable reduction in extracellular dopamine levels developed dyskinesias. On the other hand, apomorphine caused moderate to severe dyskinesias in both groups. Importantly, single-dose L-DOPA challenge in apomorphine-primed shTH animals failed to activate the already established abnormal postsynaptic responses. Taken together, these data provide direct evidence that the status of the presynaptic, DA releasing compartment is a critical determinant of both the induction and maintenance of L-DOPA-induced dyskinesias.

Intracortical inhibition of the motor cortex in Segawa disease (DYT5)

BACKGROUND

Segawa disease (autosomal dominant guanosine triphosphate cyclohydrolase I [GTP-I] deficiency, DYT5) is a hereditary dopa-responsive generalized dystonia.

OBJECTIVE

To investigate the pathophysiologic mechanisms for dystonia in Segawa disease, we studied intracortical inhibition of the primary motor cortex in patients with Segawa disease.

METHODS

We studied 9 patients with Segawa disease (8 genetically confirmed patients and 1 with abnormally low GTP-I activity) and 12 age-matched normal control subjects. We studied the active motor threshold (AMT) using single pulse transcranial magnetic stimulation (TMS) and the short-interval intracortical inhibition (SICI) of the motor cortex using the previously reported paired pulse TMS method. Responses were recorded from the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles.

RESULTS

The AMT was not significantly different between the patients and normal subjects. For both studied muscles, in Segawa disease, normal amount of SICI was evoked at interstimulus intervals (ISIs) of 1 to 4 msec even though they had dystonia in those muscles.

CONCLUSION

Normal SICI of the motor cortex in Segawa disease stands in remarkable contrast to the previously reported reduction of SICI in focal dystonia. This suggests that the gamma-aminobutyric acid A system of the motor cortex is intact in Segawa disease. The pathophysiologic mechanisms for dystonia must be partly different between Segawa disease and focal dystonia.

A case of late-onset Segawa syndrome (autosomal dominant dopa-responsive dystonia) with a novel mutation of the GTP-cyclohydrase I (GCH1) gene

We report a case of a 46-year-old Japanese woman with hereditary progressive dystonia with marked diurnal fluctuations and dopa-responsive dystonia (HPD/DRD). She developed difficulty in walking at the age of 44 years due to bradykinesia as well as hand tremors, muscle rigidity, increased tendon reflexes and mild dystonia in the lower extremities, all of which responded remarkably to low doses of levodopa (150 mg/day). Biopterin and neopterin concentrations in the cerebrospinal fluid (CSF) were decreased. Analysis of the guanosine 5'-triphosphate cyclohydrolase I (GCH1) gene revealed a novel mutation (W53X) in one allele. The GCH1 activity that was expressed in mononuclear blood cells was almost half the normal value (usually 2-20% of the normal value (39.0+/-9.2 pmol/ml) in patients with HPD/DRD). The relatively conserved GCH1 activity that is expressed in stimulated peripheral blood mononuclear cells may be related to the late clinical symptoms in this patient.

A systematic review on the diagnosis and treatment of primary (idiopathic) dystonia and dystonia plus syndromes: report of an EFNS/MDS-ES Task Force

To review the literature on primary dystonia and dystonia plus and to provide evidence-based recommendations. Primary dystonia and dystonia plus are chronic and often disabling conditions with a widespread spectrum mainly in young people. Computerized MEDLINE and EMBASE literature reviews (1966-1967 February 2005) were conducted. The Cochrane Library was searched for relevant citations. Diagnosis and classification of dystonia are highly relevant for providing appropriate management and prognostic information, and genetic counselling. Expert observation is suggested. DYT-1 gene testing in conjunction with genetic counselling is recommended for patients with primary dystonia with onset before age 30 years and in those with an affected relative with early onset. Positive genetic testing for dystonia (e.g. DYT-1) is not sufficient to make diagnosis of dystonia. Individuals with myoclonus should be tested for the epsilon-sarcoglycan gene (DYT-11). A levodopa trial is warranted in every patient with early onset dystonia without an alternative diagnosis. Brain imaging is not routinely required when there is a confident diagnosis of primary dystonia in adult patients, whereas it is necessary in the paediatric population. Botulinum toxin (BoNT) type A (or type B if there is resistance to type A) can be regarded as first line treatment for primary cranial (excluding oromandibular) or cervical dystonia and can be effective in writing dystonia. Actual evidence is lacking on direct comparison of the clinical efficacy and safety of BoNT-A vs. BoNT-B. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for generalized or cervical dystonia, after medication or BoNT have failed to provide adequate improvement. Selective peripheral denervation is a safe procedure that is indicated exclusively in cervical dystonia. Intrathecal baclofen can be indicated in patients where secondary dystonia is combined with spasticity. The absolute and comparative efficacy and tolerability of drugs in dystonia, including anticholinergic and antidopaminergic drugs, is poorly documented and no evidence-based recommendations can be made to guide prescribing.

Presynaptic mechanisms of motor fluctuations in Parkinson’s disease: a probabilistic model

Levodopa-treated Parkinson's disease is often complicated by the occurrence of motor fluctuations, which can be predictable ('wearing-off') or unpredictable ('on-off'). In contrast, untreated dopa-responsive dystonia (DRD) is usually characterized by predictable diurnal fluctuation. The pathogenesis of motor fluctuations in treated Parkinson's disease and diurnal fluctuation in untreated DRD is poorly understood. We have developed a mathematical model indicating that all these fluctuations in motor function can be explained by presynaptic mechanisms. The model is predicated upon the release of dopamine being subject to probabilistic variations in the quantity of dopamine released by exocytosis of vesicles. Specifically, we propose that the concentration of intravesicular dopamine undergoes dynamic changes according to a log-normal distribution that is associated with different probabilities of release failure. Changes in two parameters, (i) the proportion of vesicles that undergo exocytosis per unit of time and (ii) the proportion of dopamine subject to re-uptake from the synapse, allowed us to model different curves of levodopa response, for the same degree of nigrostriatal damage in Parkinson's disease. The model predicts the following periods of levodopa clinical benefit: 4 h for stable responders, 3 h for wearing-off fluctuators, and 1.5 h for on-off fluctuators. The model also predicts that diurnal fluctuation in untreated DRD should occur some 8 h after getting up in the morning. All these results fit well with clinical observations. Additionally, we calculated the probability of obtaining a second ON period after a single dose of levodopa in Parkinson's disease (the 'yo-yoing' phenomenon). The model shows that the yo-yoing phenomenon depends on how fast the curve crosses the threshold that separates ON and OFF states, which explains why this phenomenon is virtually exclusive to patients with on-off fluctuations. The model supports the idea that presynaptic mechanisms play a key role in both short-duration and long-duration responses encountered in Parkinson's disease. Dyskinesias may also be explained by the same mechanisms.

VMAT2 binding is elevated in dopa-responsive dystonia: visualizing empty vesicles by PET

Dopa-responsive dystonia (DRD) is a lifelong disorder in which dopamine deficiency is not associated with neuronal loss and therefore it is an ideal human model for investigating the compensatory changes that occur in response to this biochemical abnormality. Using positron emission tomography (PET), we examined the (+/-)-alpha-[(11)C]dihydrotetrabenazine ([(11)C]DTBZ) binding potential of untreated DRD patients and normal controls. Two other PET markers of presynaptic nigrostriatal function, d-threo-[(11)C]methylphenidate ([(11)C]MP) and 6-[(18)F]fluoro-L-dopa ([(18)F]-dopa), and [(11)C]raclopride were also used in the study. We found increased [(11)C]DTBZ binding potential in the striatum of DRD patients. By contrast, no significant changes were detected in either [(11)C]MP binding potential or [(18)F]-dopa uptake rate constant. In addition, we found evidence for increased dopamine turnover in one DRD patient by examining changes in [(11)C]raclopride binding potential in relation to levodopa treatment. We propose that the increase in [(11)C]DTBZ binding likely reflects the dramatic decrease in the intravesicular concentration of dopamine that occurs in DRD; upregulation of vesicular monoamine transporter type 2 (VMAT2) expression may also contribute. Our findings suggest that the striatal expression of VMAT2 (as estimated by [(11)C]DTBZ binding) is not coregulated with dopamine synthesis. This is in keeping with a role for VMAT2 in other cellular processes (i.e., sequestration and release from the cell of potential toxic products), in addition to its importance for the quantal release of monoamines.

Dystonia: clinical features, genetics, and treatment

PURPOSE OF REVIEW

The present review covers recent advances in dystonia research related to dystonia genetics and treatment. These have led to the discovery of novel dystonia genes and loci, to changing classification schemes, and to the introduction of improved and new treatment options.

RECENT FINDINGS

Currently 13 different forms of dystonia can be distinguished on a genetic basis (dystonia types 1-13). Recently, a novel gene locus (DYT13) was detected in a family with segmental dystonia, and the gene causing myoclonus-dystonia was identified (SGCE). Furthermore, a novel mutation in the DYT1 gene is associated with a myoclonus-dystonia phenotype. Regarding dystonia treatment, patients refractory to botulinum toxin type A can now be treated with botulinum toxin type B. Selective peripheral denervation remains an effective form of treatment for patients with secondary, but probably not with primary botulinum toxin treatment failure. Finally, a renaissance of functional surgical ablative procedures has taken place, with high frequency deep brain stimulation being introduced in dystonia treatment. Bilateral pallidotomy or pallidal stimulation may provide major benefit especially in patients with generalized, disabling dystonia with the most dramatic improvements in dystonia type 1 patients. Neurostimulation may also be effective in primary segmental axial dystonia, myoclonus-dystonia, and tardive dystonia.

SUMMARY

The recent mapping of additional dystonia gene loci, the identification of novel dystonia genes, and the characterization of proteins encoded by these genes have enhanced our understanding of various forms and aspects of the dystonias and have opened up new avenues for research. Treatment options include both medical and surgical therapies, with deep brain simulation being the most recent development.

Evolution of the response to levodopa during the first 4 years of therapy

The short-duration response, long-duration response, and dyskinetic response to levodopa change during long-term levodopa therapy. How these responses evolve, and which changes contribute to the emergence of motor fluctuations, remain unclear. We studied 18 subjects with Parkinson's disease before they began levodopa therapy and after 6, 12, 24, and 48 months of long-term levodopa therapy. The responses to 2-hour levodopa infusions after overnight and after 3 days of levodopa withdrawal were studied from 6 months onward. The mean magnitude of the short-duration response and the long-duration response measured after overnight without antiparkinsonian medications did not change during the 4 years. However, after 3 days without levodopa, it was apparent that the short-duration-response magnitude was progressively increasing (p < 0.0001) and that the long-duration response was decaying more rapidly (p = 0.0004). The short-duration-response magnitude at 4 years was inversely related to the long-duration-response magnitude (p = 0.022), suggesting that the long-duration response was one determinant of the short-duration-response magnitude. Dyskinesia increased progressively in severity during the study (p = 0.013). The duration of the short-duration response and dyskinesia did not change during the 4 years. Subject reports of motor fluctuations tended to be associated with a large short-duration response (p = 0.054). We suggest that a larger long-duration response, rather than a shortened one, is more important to the development of fluctuations. Improving the baseline or practical-off motor function to reduce the magnitude of the short-duration response may be a strategy to treat fluctuations.