Effect of thalamotomy on focal hand dystonia in a family with DYT1 mutation

We report the clinical and molecular features of a family with focal hand dystonia caused by DYT1 mutation. Four members of a family who underwent thalamotomy showed a marked and sustained therapeutic benefit that lasted for up to 12 years without recurrence of dystonia or any significant surgical complication. The hand dystonia caused by DYT1 mutation may be successfully managed by thalamotomy. © 2008 Movement Disorder Society     

Disturbed surround inhibition in focal hand dystonia

Disturbances in surround inhibition could account for various movement disorders. Here we test the functional operation of surround inhibition in focal hand dystonia. Transcranial magnetic stimulation was set to be triggered by self-initiated voluntary flexion of the index finger. During this movement, motor-evoked potential amplitudes from the little finger muscle were significantly suppressed in healthy subjects but enhanced in dystonia patients. This result supports the idea that disturbed surround inhibition is a principal pathophysiological mechanism of dystonia.     

Pseudodystonic hand posturing contralateral to a metastasis of the parietal association cortex

A 56 year-old patient, with a history of surgically removed breast cancer three years earlier, presented with incoordination of hand movements while playing piano. Neurological examination disclosed mild position sensory loss and limb-kinetic apraxia of the distal part of the right upper extremity. The most conspicuous neurological sign was a dystonic posturing of the right hand, which was only elicited when the patient outstretched her arms with the eyes closed. MRI revealed a metastatic lesion involving the left parietal cortex. The association of focal dystonic postures with lesions of the parietal association cortex indicates that dystonia may feature damage of brain cortical areas far from the basal ganglia. In addition, this provides support to the hypothesis that impairment of sensory pathways may play a role in the origin of some hyperkinetic movement disorders, such as dystonia and athetosis.     

Abnormal functional connectivity in focal hand dystonia: Mutual information analysis in EEG

The aim of the present study was to investigate functional connectivity in focal hand dystonia patients to understand the pathophysiology underlying their abnormality in movement. We recorded EEGs from 58 electrodes in 15 focal hand dystonia patients and 15 healthy volunteers during rest and a simple finger‐tapping task that did not induce any dystonic symptoms. We investigated mutual information, which provides a quantitative measure of linear and nonlinear coupling, in the alpha, beta, and gamma bands. Mean mutual information of all 58 channels and mean of the channels of interest representative of regional functional connectivity over sensorimotor areas (C3, CP3, C4, CP4, FCz, and Cz) were evaluated. For both groups, we found enhanced mutual information during the task compared with the rest condition, specifically in the beta and gamma bands for mean mutual information of all channels, and in all bands for mean mutual information of channels of interest. Comparing the focal hand dystonia patients with the healthy volunteers for both rest and task, there was reduced mutual information in the beta band for both mean mutual information of all channels and mean mutual information of channels of interest. Regarding the properties of the connectivity in the beta band, we found that the majority of the mutual information differences were from linear connectivity. The abnormal beta‐band functional connectivity in focal hand dystonia patients suggests deficient brain connectivity. © 2011 Movement Disorder Society     

Abnormality of motor cortex excitability in peripherally induced dystonia.

It is widely accepted that peripheral trauma such as soft tissue injuries can trigger dystonia, although little is known about the underlying mechanism. Because peripheral injury only rarely appears to elicit dystonia, a predisposing vulnerability in cortical motor areas might play a role. Using single and paired-pulse pulse transcranial magnetic stimulation, we evaluated motor cortex excitability of a hand muscle in a patient with peripherally induced foot dystonia, in her brother with craniocervical dystonia, and in her unaffected sister, and compared their results to those from a group of normal subjects. In the patient with peripherally induced dystonia, we found a paradoxical intracortical facilitation at short interstimulus intervals of 3 and 5 milliseconds, at which regular intracortical inhibition (ICI) occurred in healthy subjects. These findings suggest that the foot dystonia may have been precipitated as the result of a preexisting abnormality of motor cortex excitability. Furthermore, the abnormality of ICI in her brother and sister indicates that altered motor excitability may be a hereditary predisposition. The study demonstrates that the paired-pulse technique is a useful tool to assess individual vulnerability, which can be particularly relevant when the causal association between trauma and dystonia is less evident.     

The split hand in ALS has a cortical basis

Loss of highly fractionated movement involving the thumb and index finger is an early characteristic of hand dysfunction in many ALS patients. These movements are largely subserved by the ‘thenar complex’ including the first dorsal interosseus muscle (FDI), whereas the ‘hypothenar complex’, innervated by the same myotome, has less ability to fractionate and is relatively spared. This suggests that in ALS, hand dysfunction and wasting is related to corticomotoneuronal representation and input. To determine whether corticomotoneuronal input to the thenar spinal pool is preferentially impaired compared to the hypothenar spinal pool in ALS, we studied 18 ALS patients and 11 normal subjects. Compound muscle action potentials (CMAPs) and motor evoked potentials (MEPs) of the thenar and hypothenar complexes were evoked by peripheral nerve stimulation and transcranial magnetic stimulation. In healthy control subjects the cortical/peripheral (MEP/CMAP) ratios were significantly larger for the thenar complex suggesting a stronger corticomotoneuronal input to this muscle complex (P<0.005). This was not the case in ALS patients. Comparing the ratios between control subjects and patients revealed a significant reduction for the thenar complex (P<0.02) in ALS patients but not for the hypothenar complex. We conclude that corticomotoneuronal input to the thenar complex is preferentially affected in ALS and that corticomotoneuronal disease may be the prime determinant of hand dysfunction and wasting.     

The appearance of new phantom fingers post-amputation in a phocomelus

We report the unusual case of a woman with right upper limb phocomelia who, post-amputation of her right hand following trauma, sprouted a phantom hand that contained five digits, including a phantom thumb and index finger that had been absent since her birth. These two phantom digits were initially half normal size, however, more than three decades later, with mirror visual feedback treatment, she was able to elongate them to normal length. This suggests that a hardwired representation of a complete hand had always been present in her brain, but inhibited by the presence of afferents from the phocomelic hand. Amputation of the phocomelic hand then led to disinhibition of this dormant representation, and the emergence of a phantom hand with five fingers, which was then further enhanced by false visual feedback from a mirror. The case powerfully demonstrates the interaction of nature and nurture in creating and sustaining body image.     

The appearance of new phantom fingers post-amputation in a phocomelus

We report the unusual case of a woman with right upper limb phocomelia who, post-amputation of her right hand following trauma, sprouted a phantom hand that contained five digits, including a phantom thumb and index finger that had been absent since her birth. These two phantom digits were initially half normal size, however, more than three decades later, with mirror visual feedback treatment, she was able to elongate them to normal length. This suggests that a hardwired representation of a complete hand had always been present in her brain, but inhibited by the presence of afferents from the phocomelic hand. Amputation of the phocomelic hand then led to disinhibition of this dormant representation, and the emergence of a phantom hand with five fingers, which was then further enhanced by false visual feedback from a mirror. The case powerfully demonstrates the interaction of nature and nurture in creating and sustaining body image.     

Difference in intracortical inhibition of the motor cortex between cortical myoclonus and focal hand dystonia.

OBJECTIVE: The short interval intracortical inhibition (SICI) of the motor cortex (M1) is reduced in both cortical myoclonus and focal hand dystonia. This reduction has been attributed to the dysfunction of GABAergic system within the motor cortex. However, the precise mechanisms underlying the reduction may not be entirely identical in these two disorders, being due to primary pathological involvement in M1 or secondary to functional changes outside M1. The aim of this study was to elucidate possible differences in intracortical inhibition between these two disorders. METHODS: Subjects were 11 patients with benign myoclonus epilepsy, 7 with focal hand dystonia, and 11 normal volunteers. We studied SICI using anterior-posterior (AP) directed and posterior-anterior (PA) directed induced currents in the brain. RESULTS: In both disorders, SICI with PA-directed currents was reduced as reported previously. In contrast, SICI studied with AP currents was normal in patients with focal hand dystonia, but reduced in patients with cortical myoclonus. CONCLUSIONS: The difference between the two disorders might reflect the underlying pathological difference. In cortical myoclonus, the inhibitory interneurons of the motor cortex are affected, whereas the same interneurons are intact in dystonia. The difference in SICI induced by AP and PA directed currents in dystonia may be explained by the following possibilities: the difference in composition of I-waves contributing to EMG generation and the difference in modulation of the interneuronal activity by voluntary contraction. These changes may be secondary to dysregulation of the motor cortex by the basal ganglia or related cortices in dystonia. SIGNIFICANCE: The SICI using AP directed currents together with the conventional SICI using PA directed currents was able to demonstrate some difference in the intrinsic circuits of M1 between myoclonus and focal hand dystonia. SICI using AP directed currents can provide additional information about the motor cortical excitability changes over those obtained by the previously reported methods.     

Loss and recovery of voluntary hand movements in the macaque following a cervical dorsal rhizotomy

The recovery of manual dexterity was analyzed in the macaque following a cervical dorsal root section that abolished cutaneous feedback from selected digits of one hand. Monkeys were trained to retrieve a target object from a clamp using thumb and index finger opposition. Dorsal rootlets containing electrophysiologically identified axons projecting from the thumb and index finger were then cut in two monkeys (Group 1). In four others (Group 2), additional rootlets shown to innervate the middle finger and thenar eminence were also transected. Three performance parameters were analyzed before and following the rhizotomy: 1) percentage of successful retrievals; 2) digital stratagem (the pattern of digit opposition); and 3) contact time (duration of digit contact with the object before its retrieval). During the first postoperative week, hand function was severely impaired in all monkeys. Over the following weeks, Group 1 monkeys recovered the ability to retrieve the object by opposing the index finger and thumb in >80% of trials. Group 2 monkeys also regained some function in the impaired hand: each monkey adopted a stratagem for grasping the target, using digits that were incompletely deafferented. In the terminal experiment, hand representation in the contralateral somatosensory cortex was electrophysiologically mapped to define hand deafferentation and cortical reactivation further. There was a close correspondence between the cortical map and digit use. Our data imply that the recovery of precision grip using the thumb and index finger depends on the survival of afferents innervating these digits, as well as the proliferation of their central terminals.     

Does acute peripheral trauma contribute to idiopathic adult-onset dystonia?

BackgroundAcute peripheral trauma is a controversial risk factor for idiopathic dystonia.Materials and methodsWe retrospectively analyzed data from the Italian Dystonia Registry regarding the occurrence of acute peripheral trauma severe enough to require medical attention in 1382 patients with adult-onset idiopathic dystonia and 200 patients with acquired adult-onset dystonia.ResultsPatients with idiopathic and acquired dystonia showed a similar burden of peripheral trauma in terms of the number of patients who experienced trauma (115/1382 vs. 12/200, p = 0.3) and the overall number of injuries (145 for the 1382 idiopathic patients and 14 for the 200 patients with secondary dystonia, p = 0.2). Most traumas occurred before the onset of idiopathic or secondary dystonia but only a minority of such injuries (14 in the idiopathic group, 2 in the acquired group, p = 0.6) affected the same body part as that affected by dystonia. In the idiopathic group, the elapsed time between trauma and dystonia onset was 8.1 ± 9.2 years; only six of the 145 traumas (4.1%) experienced by 5/1382 idiopathic patients (0.36%) occurred one year or less before dystonia onset; in the acquired dystonia group, the two patients experienced prior trauma to the dystonic body part 5 and 6 years before dystonia development.Discussion and conclusionOur data suggest that the contribution of peripheral acute trauma to idiopathic dystonia is negligible, if anything, and likely involves only a small subset of patients.     

Spatial discrimination is abnormal in focal hand dystonia

BACKGROUND: In patients with focal hand dystonia, abnormal digit representations in the primary somatosensory cortex (S1) could be the result of enlarged and overlapping receptor fields, as suggested by an animal model of dystonia. A possible clinical correlate of this S1 abnormality is a disturbed spatial discrimination capability. OBJECTIVE: To test the hypothesis that somatosensory spatial discrimination is abnormal in focal hand dystonia. METHODS: Seventeen patients with focal hand dystonia underwent a quantitative evaluation of somatosensory spatial frequency (gap detection, JVP domes, applied to the distal phalanx of the index finger) and single-touch localization (Von Frey monofilaments, applied to the middle phalanx of the index finger). RESULTS: Compared with control subjects, patients had a decreased performance in both the gap detection (p = 0.004) and the localization (p = 0.013) tasks. The extent of spatial frequency abnormality correlated with age in both groups. CONCLUSIONS: These findings, together with a previously shown temporal discrimination deficit, support a role for sensory dysfunction in the pathophysiology of dystonia.     

Abnormal reorganization in focal hand dystonia--sensory and motor training programs to retrain cortical function

Dystonia is a disabling movement disorder, which is characterized by an abnormal pattern of muscle activity with co-contraction of agonist and antagonist muscles. In the case of focal hand dystonia (FHD), these abnormal movements affect muscles of the forearm and hand while performing a specific task. Patients may initially present with dystonic symptoms occurring with a selective task (simple writer's cramp or musician's cramp), and may progress to develop symptoms with multiple tasks (dystonic writer's cramp). The underlying cause of this disabling condition remains unclear. This review examines recent studies designed to further elucidate the underlying pathophysiological processes in focal dystonia. Animal research work, and neurophysiological and neuroimaging studies in humans, have identified several possible mechanisms that may contribute to the underlying pathophysiology, including impaired sensorimotor integration, motor cortex activation and surround inhibition. Pharmacological treatment for dystonia is currently suboptimal. Based on these recent pathophysiological findings, several promising and novel non-pharmacological treatment modalities have recently been developed. Attempts at modulating impaired sensorimotor integration and cortical inhibition using sensorimotor retraining, and the range of sensory training techniques recently described, are further discussed in this review.     

Functional localization of the sensory hand area with respect to the motor central gyrus knob

The aim of this work was to investigate the topography of the primary sensory hand cortex with magnetoencephalography in order to define the functional anatomy of this area in healthy humans. Previous studies denoted an inverted Ohm or an horizontal epsilon shaped knob on the pre-central gyrus as a landmark for the motor hand area; therefore a systematic difference between the orientation of the source for thumb with respect to little finger should be observed. We found this systematic difference, but the direction of the sources activated during thumb and little finger stimulation did not converge, as would be expected if only the Ohm convexity is activated: in fact our results suggest that thumb sensory area also extends to the area lateral to this convexity.     

The relationship of peripheral trauma and pain to dystonia.

Four patients are described who sustained comparatively minor peripheral injury, the affected area soon becoming the site of segmental dystonia. The movement disorder developed as the symptoms from the injury subsided, and except for the recent trauma, no cause for the dystonia was apparent; litigation was not an issue for any patient. It is suggested that on rare occasions peripheral trauma results in the development of dystonia. Since injury never involved the head, the role of the spinal dopaminergic system and the relevance of pain from the injury are discussed in considering possible underlying mechanisms.     

Delayed onset limb dystonia following electric injury

It has been recognized that head trauma can induce movement disorders including tremor, dystonia, parkinsonism and tics. Likewise, lesions involving the peripheral nervous system have been held responsible for such extrapyramidal manifestations, However, involuntary movements secondary to electric injury have seldom been described. Here we report a patient who developed limb dystonia 6 years after receiving an electric discharge in the ipsilateral limb. Although imaging and laboratory studies failed to ascribe the lesion either to the central or peripheral nervous system, initial symptoms such as local bruises, edema and pain would favor peripheral damage. Botulinum toxin injections markedly improved dystonia. Analysis of cases of dystonia following electric injury reported to date suggest that: (a) dystonia may be expected to develop immediately or even years after the electric insult; (b) dystonia usually develops in or adjacent to the area initially injured; (c) dystonia remains limited to a distinct body segment; (d) severity of dystonia as well as the interval between injury and the onset of the movement disorder fails to correlate with trauma severity; (e) no evidence supports the hypothesis that previous history of movement disorders or neuroleptic exposure are predisposing factors; and (f) botulinum toxic provides symptomatic relief.     

Representation of the hand in the cerebral cortex

In this brief review, the body of work on hand use and cortical plasticity is reviewed. The hand movements and sensory inputs are represented in the mammalian primary motor cortex and the anterior parietal strip. The dominant organizational rules are that representational area is proportional to peripheral innervation, and that cortical architecture is columnar with limited horizontal spread. The representational area and columnar structure can be shaped by behavior and other input manipulations. The central core systems, and especially cholinergic inputs, act as teachers of the cerebral cortex by marking behavioral reinforcers with the release of acetylcholine. This marking is both necessary and sufficient for plasticity to occur in sensory cortex. As a result of this temporal marking of reinforcing events, nearly coincident inputs over restricted sensory, or motor, segments form coherent representations in primary sensory or motor cortex. Focal dystonia is a problem in which overuse of the hand leads to a lack of motor control, and especially inappropriate use of sensory feedback for motor control. Receptive field size, and columnar architecture, are highly abnormal in this disorder. The deficiencies in focal dystonia, and their appropriate treatment, can be understood by applying the principles of cortical plasticity to the behavioural manipulations that cause focal dystonia.     

Un cas de crampe des écrivains dystonique combinée à un syndrome du canal carpien à Ouagadougou (Burkina Faso)

Introduction

Focal hand dystonia and carpal tunnel syndrome are linked to impairment of the central and peripheral nervous systems, respectively. We report a singular case combining these two entities.

Case report

A 44-year-old right-handed male pharmacy employee whose daily activity for 18 years was to fill out and staple insurance vouchers and unload and store boxes of medicines, presented, almost concomitantly, the combination of right focal hand dystonia and homolateral carpal tunnel syndrome.

Conclusion

This observation corroborates the results of experimental studies on repetitive manual activity which would be a source of central and peripheral changes, affecting the hand somatotopy in the sensory-motor cortex and the descending control of basal ganglia, explaining dystonia, and leading to median nerve compression related to repeated microtrauma, inflammatory reactions and fibrosis of the carpal tunnel.     

Oscillatory interaction between the hand area of human primary motor cortex and finger muscles during steady-state isometric contraction

Objective

To compare the magnitudes of β-band coherence between the primary motor cortex (M1) and electromyogram (EMG) for finger muscles, and to determine whether M1–EMG coherence is related to the stability of muscle contraction.

Methods

Cortical signals and EMG during steady-state isometric contraction of right thumb muscle (flexor pollicis brevis (FPB)) or right little finger muscle (flexor digiti minimi brevis (FDMB)) were recorded simultaneously with magnetoencephalography system from 13 right-handed healthy subjects.

Results

The magnitudes of β-band M1–EMG coherence and spectral power in the M1 for the FPB muscle were greater than that for the FDMB muscle (P < 0.001 and P < 0.005, respectively). The stability of EMG for the FPB was higher than that for FDMB (P < 0.001). Greater levels of β-band M1–EMG coherence were associated with higher levels of EMG stability (P < 0.05). The mean dipole sources of the FPB muscle were located more laterally, inferiorly and anteriorly than that of FDMB in the M1 hand area (P < 0.005).

Conclusions

The strength of β-band M1–EMG coherence would play an important role in the stability level of finger-muscle contraction.

Significance

The β-band M1–EMG coherence may reflect effective oscillatory interaction between the M1 and finger muscle during steady-state motor output.     

Anatomical Functional Changes in a Patient Presenting a Complex Malformation of Cortical Development

The authors describe a case of right fronto‐parietal micropoligyria associated with small schizencephaly clefts and the presence of a frontal open‐lip schizencephaly with corpus callosum agenesis. A functional magnetic resonance imaging (fMRI) study was performed to evaluate the possible reorganization of cortical functions in a patient presentinga complex malformation pattern and to investigate which cortical areas were activated during left finger movements. An fMRI study was performed during the execution of a repetitive index finger‐to‐thumb opposition movement with the right hand and the left hand in 2 separate sessions. Movement of the right hand induced a normal motor activation pattern involving the contralateral left sensory‐motor cortex. Movement of the left hand produced significant activation of brain cortex. This fMRI study highlights the compensatory role of the ipsilateral cortical pathways in hand movements in the case of a complex brain malformation that involves the main motor activation areas.