Cortical excitability is abnormal in patients with the "fixed dystonia" syndrome

Normal eyeblink classical conditioning in patients with fixed dystonia

Fixed dystonia without evidence of basal ganglia lesions or neurodegeneration typically affects young women following minor peripheral trauma. We use eyeblink classical conditioning (EBCC) to study whether cerebellar functioning is abnormal in patients with fixed dystonia, since this is part of the pathophysiology of primary dystonia. An auditory tone (conditioning stimulus) was paired with a supraorbital nerve stimulus (unconditioned stimulus) with a delay of 400 ms in order to yield conditioned responses. We recruited 11 fixed dystonia patients of whom six used medication and seven age-matched healthy controls. Non-medicated patients with fixed dystonia performed as well as healthy controls, while medicated patients showed fewer conditioned responses. We found an influence of medication and possibly extent of dystonic features and/or co-occurrence of complex regional pain syndrome (CRPS) on EBCC performance. Our study argues against abnormal cerebellar function in non-medicated, fixed dystonia patients without CRPS or spread of symptoms.

The functional neuroimaging correlates of psychogenic versus organic dystonia

The neurobiological basis of psychogenic movement disorders remains poorly understood and the management of these conditions difficult. Functional neuroimaging studies have provided some insight into the pathophysiology of disorders implicating particularly the prefrontal cortex, but there are no studies on psychogenic dystonia, and comparisons with findings in organic counterparts are rare. To understand the pathophysiology of these disorders better, we compared the similarities and differences in functional neuroimaging of patients with psychogenic dystonia and genetically determined dystonia, and tested hypotheses on the role of the prefrontal cortex in functional neurological disorders. Patients with psychogenic (n = 6) or organic (n = 5, DYT1 gene mutation positive) dystonia of the right leg, and matched healthy control subjects (n = 6) underwent positron emission tomography of regional cerebral blood flow. Participants were studied during rest, during fixed posturing of the right leg and during paced ankle movements. Continuous surface electromyography and footplate manometry monitored task performance. Averaging regional cerebral blood flow across all tasks, the organic dystonia group showed abnormal increases in the primary motor cortex and thalamus compared with controls, with decreases in the cerebellum. In contrast, the psychogenic dystonia group showed the opposite pattern, with abnormally increased blood flow in the cerebellum and basal ganglia, with decreases in the primary motor cortex. Comparing organic dystonia with psychogenic dystonia revealed significantly greater regional blood flow in the primary motor cortex, whereas psychogenic dystonia was associated with significantly greater blood flow in the cerebellum and basal ganglia (all P < 0.05, family-wise whole-brain corrected). Group × task interactions were also examined. During movement, compared with rest, there was abnormal activation in the right dorsolateral prefrontal cortex that was common to both organic and psychogenic dystonia groups (compared with control subjects, P < 0.05, family-wise small-volume correction). These data show a cortical–subcortical differentiation between organic and psychogenic dystonia in terms of regional blood flow, both at rest and during active motor tasks. The pathological prefrontal cortical activation was confirmed in, but was not specific to, psychogenic dystonia. This suggests that psychogenic and organic dystonia have different cortical and subcortical pathophysiology, while a derangement in mechanisms of motor attention may be a feature of both conditions.

Transcranial magnetic stimulation in dystonia

Transcranial magnetic stimulation (TMS) is a method of noninvasive brain stimulation that directly affects the cerebral cortex but not deep structures. TMS has been used extensively in patients with primary dystonia to test the excitability of connections within and among motor areas of the cortex, and has provided useful information on pathophysiology; however, interindividual variability in the responses has resulted in difficulties in translating this method into a clinically applicable diagnostic use. In addition, TMS studies have disclosed that dystonia is a disorder linked to a disruption of synaptic "scaling," with an excess of synaptic plasticity that is in keeping with findings obtained in animal models of dystonia. This alteration is a unique feature of organic dystonia and may be helpful in differentiating patients with psychogenic dystonia. Finally, TMS can potentially be used as a therapeutic tool to treat some forms of dystonia, such as focal hand dystonia, where pharmacological options or injections of botulinum toxin are often ineffective.

Functional (psychogenic) movement disorders

PURPOSE OF REVIEW

This review provides an overview of recent developments in diagnosis, pathophysiology, neuroimaging and management of functional (psychogenic) movement disorders (FMD).

RECENT FINDINGS

There has been increasing interest to study the underlying pathophysiology of FMD, which has resulted in a broadened disease model, taking neurobiologic and psychosocial factors equally into account. In this context, the term 'psychogenic' has been replaced by 'functional' movement disorders by many authors in the field to express the changing focus toward a multifactorial disease model. The need for establishing a positive diagnosis of FMD as opposed to providing a diagnosis of exclusion is increasingly recognized and reflected by the introduction of 'laboratory-supported' diagnostic criteria of FMD. Important advances have been made through behavioral, electrophysiological and neuroimaging studies, although the fundamental cause of FMD remains poorly understood. Of particular interest have been several reports on abnormal sensorimotor features and cortical inhibition in both organic and functional dystonia, highlighting possible shared traits of both conditions. In terms of treatment, recent studies have reported benefit from both psychiatric and physical therapy-based interventions.

SUMMARY

Increasing efforts have been made toward better understanding of FMD, and the disease model has been broadened to include neurobiologic and psychosocial factors. Laboratory-based diagnostic criteria have been established for many FMD to support the clinical diagnosis. To determine the most effective management strategies for FMD, a closer collaboration between neurologists and psychiatrists and intensified research efforts with prospective treatment trials are needed.

Functional (psychogenic) movement disorders: merging mind and brain

Functional (psychogenic) movement disorders (FMD) are part of the wide spectrum of functional neurological disorders, which together account for over 16% of patients referred to neurology clinics. FMD have been described as a "crisis for neurology" and cause major challenges in terms of diagnosis and treatment. As with other functional disorders, a key issue is the absence of pathophysiological understanding. There has been an influential historical emphasis on causation by emotional trauma, which is not supported by epidemiological studies. The similarity between physical signs in functional disorders and those that occur in feigned illness has also raised important challenges for pathophysiological understanding and has challenged health professionals' attitudes toward patients with these disorders. However, physical signs and selected investigations can help clinicians to reach a positive diagnosis, and modern pathophysiological research is showing an appreciation of the importance of both physical and psychological factors in FMD.

Psychogenic movement disorders: past developments, current status, and future directions

As the field of movement disorders has developed and matured over the past 25 years, psychogenic movement disorders have become increasingly recognized in subspecialty clinics. The diagnosis can be challenging and should be based on positive features rather than a purely exclusionary approach. The clinical phenotype can be quite varied, although certain categories of abnormal movement are more common than others. Electrophysiological studies may be particularly useful in establishing the diagnosis, especially with respect to tremor and myoclonus, and an argument can be made for adding a "laboratory-supported definite" category to earlier classification schemes. The diagnosis of psychogenic dystonia remains a major challenge, although there are some recent promising developments with respect to the evaluation of cortical plasticity that require further study. The pathogenesis of psychogenic movement disorders is poorly understood; insights may be provided from the study of other neurological conversion disorders such as psychogenic hemiparesis. Psychogenic movement disorders typically result in considerable disability and negatively impact quality of life to the same or greater extent than do many organic movement disorders. Treatment is extremely challenging, and many patients experience chronic disability despite various therapeutic interventions. Given the personal and societal impact of these problems, further advances in our understanding of their pathogenesis and the subsequent development of effective therapies are sorely needed.

Clinical features and pathophysiology of complex regional pain syndrome

A complex regional pain syndrome (CRPS)--multiple system dysfunction, severe and often chronic pain, and disability--can be triggered by a minor injury, a fact that has fascinated scientists and perplexed clinicians for decades. However, substantial advances across several medical disciplines have recently improved our understanding of CRPS. Compelling evidence implicates biological pathways that underlie aberrant inflammation, vasomotor dysfunction, and maladaptive neuroplasticity in the clinical features of CRPS. Collectively, the evidence points to CRPS being a multifactorial disorder that is associated with an aberrant host response to tissue injury. Variation in susceptibility to perturbed regulation of any of the underlying biological pathways probably accounts for the clinical heterogeneity of CRPS.

[Clinical characteristics and treatment of dystonia]

Dystonia is defined as a syndrome of sustained muscle contractions, frequently causing twisting and repetitive movements, or abnormal postures. Its diagnosis is based on clinical characteristics. In dystonia, the pattern of abnormal posture or movement tends to be constant during the short term even if its severity fluctuates. This stereotypy often helps differentiate dystonia from psychogenic reaction. Dystonia may appear only during some specific task (task specificity) especially in its early phase, although it often becomes obscure during the long clinical course, resulting in persistent dystonic posture. Sensory trick or geste antagoniste means the change of severity triggered by some sensory input Overflow phenomenon is the activation of muscles unnecessary to a task, hampering purposeful movement. Symptoms tend to be milder in the morning, with large individual variation of its duration (morning benefit). Symptoms of dystonia may abruptly appear or disappear (flip-flop phenomenon). Cocontraction, believed as an essential feature of dystonia, reflects a loss of reciprocal inhibition of muscle activities, causing involuntary simultaneous contractions of agonists and antagonists. "Negative dystonia," still an unaccepted feature of dystonia, is defined as non-paretic loss of central driving of muscle activities necessary to a task. Apraxia of lid opening/closure, paretic form of hand dystonia, dropped head syndrome, camptocormia, Pisa syndrome, cervical dystonia with limited range of head movement, or mandibular dystonia without cocontractions of masticatory muscles, can be explained with this concept at least in a subset of cases. Treatment of dystonia includes medication, botulinum toxin injection, intrathecal baclofen, surgical intervention, acupuncture and other alternative therapies, rehabilitation, and psychotherapy. Oral medication is usually an adjunct to more potent therapeutic options except for some specific indications like dopa-responsive dystonia. Botulinum toxin is usually the treatment of choice for focal dystonia. Deep brain stimulation can be considered for both focal and non-focal phenotypes of dystonia.

EFNS guidelines on diagnosis and treatment of primary dystonias

OBJECTIVES

to provide a revised version of earlier guidelines published in 2006.

BACKGROUND

primary dystonias are chronic and often disabling conditions with a widespread spectrum mainly in young people.

DIAGNOSIS

primary dystonias are classified as pure dystonia, dystonia plus or paroxysmal dystonia syndromes. Assessment should be performed using a validated rating scale for dystonia. Genetic testing may be performed after establishing the clinical diagnosis. DYT1 testing is recommended for patients with primary dystonia with limb onset before age 30, and in those with an affected relative with early-onset dystonia. DYT6 testing is recommended in early-onset or familial cases with cranio-cervical dystonia or after exclusion of DYT1. Individuals with early-onset myoclonus should be tested for mutations in the DYT11 gene. If direct sequencing of the DYT11 gene is negative, additional gene dosage is required to improve the proportion of mutations detected. A levodopa trial is warranted in every patient with early-onset primary dystonia without an alternative diagnosis. In patients with idiopathic dystonia, neurophysiological tests can help with describing the pathophysiological mechanisms underlying the disorder.

TREATMENT

botulinum toxin (BoNT) type A is the first-line treatment for primary cranial (excluding oromandibular) or cervical dystonia; it is also effective on writing dystonia. BoNT/B is not inferior to BoNT/A in cervical dystonia. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for primary generalized or cervical dystonia, after medication or BoNT have failed. DBS is less effective in secondary dystonia. This treatment requires a specialized expertise and a multidisciplinary team.

Limb amputations in fixed dystonia: a form of body integrity identity disorder?

Fixed dystonia is a disabling disorder mainly affecting young women who develop fixed abnormal limb postures and pain after apparently minor peripheral injury. There is continued debate regarding its pathophysiology and management. We report 5 cases of fixed dystonia in patients who sought amputation of the affected limb. We place these cases in the context of previous reports of patients with healthy limbs and patients with chronic regional pain syndrome who have sought amputation. Our cases, combined with recent data regarding disorders of mental rotation in patients with fixed dystonia, as well as previous data regarding body integrity identity disorder and amputations sought by patients with chronic regional pain syndrome, raise the possibility that patients with fixed dystonia might have a deficit in body schema that predisposes them to developing fixed dystonia and drives some to seek amputation. The outcome of amputation in fixed dystonia is invariably unfavorable.

The blink reflex recovery cycle differs between essential and presumed psychogenic blepharospasm

BACKGROUND

Psychogenic blepharospasm is difficult to distinguish clinically from benign essential blepharospasm (BEB). The blink reflex recovery cycle measures the excitability of human brainstem interneurons and is abnormal in BEB. We wished to study the blink reflex recovery cycle in patients with atypical (presumed psychogenic) blepharospasm (AB).

METHODS

This was a prospective data collection study investigating the R2 blink reflex recovery cycle at interstimulus intervals (ISI) of 200, 300, 500, 1,000, and 3,000 msec in 10 patients with BEB, 9 patients with AB, and 9 healthy controls. All patients had spasm of the orbicularis oculi muscles. To compare individual patients, an R2 recovery index was calculated as average of the recovery values at ISIs of 200, 300, and 500 msec, with the upper limit of normal defined as mean (control group) + 2 SD.

RESULTS

The R2 recovery cycle was significantly disinhibited in patients with BEB, whereas patients with AB did not differ from controls on a group level. The upper limit of normal for the R2 recovery index was 61%. The R2 index was abnormal in 9 out of 10 patients with BEB and in none of the patients with AB.

CONCLUSIONS

A normal blink reflex recovery cycle indicates normal brainstem interneuron excitability. Assessment of the R2 recovery cycle may provide a useful diagnostic tool to distinguish patients with psychogenic blepharospasm from BEB and is worthy of further study.

A distinctive pattern of cortical excitability in patients with the syndrome of dystonia and cerebellar ataxia

OBJECTIVE

The syndrome of dystonia and cerebellar ataxia (DYTCA) is a recently described condition where cervical dystonia and mild cerebellar ataxia are the major clinical features. Here we attempted to explore the pathophysiology of this condition by comparing measurements of cortical excitability between patients with DYTCA, typical primary dystonia and healthy controls.

METHODS

Motor threshold, active MEP recruitment and CSP duration were measured and the excitability of the intracortical inhibitory and excitatory circuits was assessed at rest using a paired pulse protocol.

RESULTS

We identified a distinctive pattern of cortical excitability in DYTCA patients different from that found in primary dystonia, namely hyperexcitable short-interval intracortical inhibition.

CONCLUSION

DYTCA patients have a noticeably dissimilar excitability profile from patients with primary dystonia.

SIGNIFICANCE

A tendency for increased SICI has been previously described in cerebellar syndromes and the altered excitability profile seen in these patients is therefore possibly a consequence of the cerebellar dysfunction in DYTCA. A direct link between reduced intracortical inhibition and dystonia has recently been questioned and our results additionally suggest that reduced motor cortex inhibition is not a prerequisite for dystonia to occur.

Movement disorders in complex regional pain syndrome

About 25% of the patients with complex regional pain syndrome (CRPS) suffer movement disorders, including loss of voluntary control, bradykinesia, dystonia, myoclonus, and tremor. These movement disorders are generally difficult to manage and add considerably to the disease burden. Over the last years, interesting findings have emerged that show how tissue or nerve injury may induce spinal plasticity (central sensitization), which alters sensory transmission and sensorimotor processing in the spinal cord and is associated with disinhibition. These changes, in turn, set the stage for the development of movement disorders seen in CRPS. There are no randomized control studies on the treatment of movement disorders in CRPS but findings from fundamental and clinical research suggest that strategies that enhance the central inhibitory state may benefit these patients.

Motor excitability during movement imagination and movement observation in psychogenic lower limb paresis

BACKGROUND

Patients with a psychogenic paresis have difficulties performing voluntary movements. Typically, diagnostic interventions are normal. We tested whether patients with a psychogenic lower limb paresis exhibit abnormal motor excitability during motor imagery or movement observation.

METHODS

Transcranial magnetic stimulation (TMS) with single and paired pulses was used to explore motor excitability at rest, during imagination of ankle dorsiflexions and during watching another person perform ankle dorsiflexions. Results obtained in ten patients with a flaccid psychogenic leg paresis were compared with a healthy age-matched control group. In addition, results of two patients with a psychogenic fixed dystonia of the leg are presented.

RESULTS

During rest, motor excitability evaluated by motor thresholds, size of motor-evoked potentials (MEP) by single pulse TMS, intracortical inhibition and intracortical facilitation tested by paired-pulse TMS were similar in patients and healthy subjects. MEPs recorded in five patients during movement observation were also comparable across the two groups. During motor imagery, patient MEPs were significantly smaller than in the control group and smaller than during rest, indicating an inhibition.

CONCLUSION

In patients with motor conversion disorder, the imagination of own body movements induces a reduction of corticospinal motor excitability whereas it induces an excitability increase in healthy subjects. This discrepancy might be the electrophysiological substrate of the inability to move voluntarily. Watching another person perform movements induces a normal excitability increase, indicating a crucial role of the perspective and suggesting that focusing the patient's attention on a different person might become a therapeutic approach.

The diagnostic challenge of primary dystonia: evidence from misdiagnosis

Although the understanding of dystonia has improved in recent years, primary dystonia is still insufficiently recognized and patients may not receive the correct diagnosis, leading to transient or permanent misclassification of their symptoms. We reviewed cases of primary dystonia who were at first misdiagnosed and analyzed the reasons why the correct diagnosis was first missed and later retained. Primary dystonia is misdiagnosed mainly, but not exclusively, in favor of other movement disorders: Parkinson's disease (PD), essential tremor, myoclonus, tics, psychogenic movement disorder (PMD), and even headache or scoliosis. Accounts are more numerous for PD and PMD, where diagnostic tests, such as DAT scan and psychological assessment, support clinical orientation. The correct diagnosis was achieved in all cases following the recognition of inconsistencies in the first judgment and of distinctive clinical features of dystonia. These clues have been collected here and assembled into a diagnostic epitome.

Focal limb dystonia

Limb dystonia (LD) refers to dystonia affecting one arm or leg. Depending on the site of onset, age at onset, and the etiology, progression and prognosis will be different. Usually young-onset primary dystonia affects the lower limbs and tends to generalize, while in adult-onset, it appears in the arm and remains focal. Lower limb dystonia in adults is rare as a primary cause, and parkinsonism or other neurological diseases must always be ruled out. In the text that follows, we review the main clinical features of the primary and secondary limb dystonias considering the age at onset and etiology.

Physiology of psychogenic movement disorders

Psychogenic movement disorders (PMDs) are common, but their physiology is largely unknown. In most situations, the movement is involuntary, but in a minority, when the disorder is malingering or factitious, the patient is lying and the movement is voluntary. Physiologically, we cannot tell the difference between voluntary and involuntary. The Bereitschaftspotential (BP) is indicative of certain brain mechanisms for generating movement, and is seen with ordinarily voluntary movements, but by itself does not indicate that a movement is voluntary. There are good clinical neurophysiological methods available to determine whether myoclonus or tremor is a PMD. For example, psychogenic myoclonus generally has a BP, and psychogenic stimulus-sensitive myoclonus has a variable latency with times similar to normal reaction times. Psychogenic tremor will have variable frequency over time, be synchronous in the two arms, and might well be entrained with voluntary rhythmic movements. These facts suggest that PMDs share voluntary mechanisms for movement production. There are no definitive tests to differentiate psychogenic dystonia from organic dystonia, although one has been recently reported. Similar physiological abnormalities are seen in both groups. The question arises as to how a movement can be produced with voluntary mechanisms, but not be considered voluntary.

Poststroke fixed dystonia of the foot relieved by chronic stimulation of the posterior limb of the internal capsule

The authors report the case of an adult patient with irreducible fixed dystonia (inward rotation) of the right foot that arose after cardioembolic ischemia of the left putamen and globus pallidus externus. Given the resistance of such symptomatology to all of the attempted conservative treatments (including botulinum toxin), the authors decided to perform deep brain stimulation, positioning the intracerebral electrode in the left internal capsule at the level of the motor fibers controlling the right foot, as confirmed by intraoperative electromyography. After the intervention, the patient was able to perform voluntary movements of outward rotation and abduction in the right foot and begin gait rehabilitation. Deep brain stimulation of the posterior limb of the internal capsule could be an alternative target used to treat poststroke fixed dystonic conditions.

Abnormal sensorimotor plasticity in organic but not in psychogenic dystonia

Dystonia is characterized by two main pathophysiological abnormalities: 'reduced' excitability of inhibitory systems at many levels of the sensorimotor system, and 'increased' plasticity of neural connections in sensorimotor circuits at a brainstem and spinal level. A surprising finding in two recent papers has been the fact that abnormalities of inhibition similar to those in organic dystonia are also seen in patients who have psychogenic dystonia. To try to determine the critical feature that might separate organic and psychogenic conditions, we investigated cortical plasticity in a group of 10 patients with psychogenic dystonia and compared the results with those obtained in a matched group of 10 patients with organic dystonia and 10 healthy individuals. We confirmed the presence of abnormal motor cortical inhibition (short-interval intracortical inhibition) in both organic and psychogenic groups. However, we found that plasticity (paired associative stimulation) was abnormally high only in the organic group, while there was no difference between the plasticity measured in psychogenic patients and healthy controls. We conclude that abnormal plasticity is a hallmark of organic dystonia; furthermore it is not a consequence of reduced inhibition since the latter is seen in psychogenic patients who have normal plasticity.

Intrathecal glycine for pain and dystonia in complex regional pain syndrome

Since glycinergic neurotransmission plays an important inhibitory role in the processing of sensory and motor information, intrathecal glycine (ITG) administration may be a potential therapy for both pain and movement disorders in patients with complex regional pain syndrome (CRPS). Aims of the current study, which is the first report on ITG in humans, were to evaluate its safety and efficacy. ITG treatment during 4 weeks was studied in CRPS patients with dystonia in the period before they received intrathecal baclofen treatment. Twenty patients were assessed and after exclusion of one patient, the remaining 19 patients were randomized in a double-blind placebo-controlled crossover study. Safety was assessed by clinical evaluation, blood examinations and electrocardiograms. Efficacy measures involved pain (numeric rating scale, McGill pain questionnaire), movement disorders (Burke-Fahn-Marsden dystonia rating scale, unified myoclonus rating scale, tremor research group rating scale), activity (Radboud skills questionnaire, walking ability questionnaire), and a clinical global impression (CGI) and patient's global impression score (PGI). Treatment-emergent adverse events were generally mild to moderate and not different from placebo treatment. During ITG treatment growth hormone levels were slightly increased. Although there was a trend to worsening on the CGI and PGI during ITG treatment, there were no significant differences between ITG and placebo treatment in any of the outcomes. ITG given over 4 weeks was ineffective for pain or dystonia in CRPS. Although no serious adverse events occurred, further studies are required to rule out potential neurotoxicity of ITG.

Consensus paper: use of transcranial magnetic stimulation to probe motor cortex plasticity in dystonia and levodopa-induced dyskinesia

Plasticity includes the ability of the nervous system to optimize neuronal activity at a cellular and system level according to the needs imposed by the environment. Neuroplasticity phenomena within sensorimotor cortex are crucial to enhance function to increase skillfulness. Such plasticity may be termed "adaptive" to indicate its ecologically beneficial role. In professional musicians, enhanced adaptive plasticity is associated with one of the highest level of motor skill a human being can achieve and the amount of these changes is even dependent on the age at which instrumental playing was started. In addition, adaptive neuroplastic changes occur when nervous system try to repair itself thus compensating dysfunctions. However, when these adaptive phenomena are pushed to an extreme, they can produce a maladaptive sensorimotor reorganization that interferes with motor performance rather than improving it. The model we discuss here is focal hand dystonia I which an intrinsic abnormality of neural plasticity, in some predisposed individuals, may lead to abnormal sensorimotor integration and to the appearance of a characteristic movement disorder. Deficient homeostatic control might be an important mechanism triggering this maladaptive reorganization, and future behavioral studies are needed to confirm this hypothesis. In the second part of this consensus paper, we will critically discuss as a second model, the hypothesis that levodopa-induced dyskinesia correlate with an aberrant form of plasticity in the human primary motor cortex, possibly because of abnormal oscillations within the basal ganglia loop. Disorders of cortical plasticity have not in the past been considered as possible causes of human clinical states. The recognition that this can occur, together with a speculative mechanism, generates an important and provocative hypothesis for future research at the clinical-scientific interface.