Hand cramps: clinical features and electromyographic patterns in a focal dystonia

We studied 19 patients with hand cramps, including writer's cramp, typist's cramp, piano, and guitar player's cramp. EMGs were recorded while patients performed the task triggering the cramps. Ten patients with dystonic cramps had EMGs with generalized muscle spasms with co-contraction of agonist and antagonist muscles. In three patients with simple cramps that involved one to three fingers, specific muscle groups showed co-contracting bursts that lasted longer than normal. The physiological abnormalities support the interpretation that hand cramp is a focal dystonia, characterized by both excessive muscle activity and defective fine motor control.     

EMG-EMG coherence in writer's cramp.

We investigated the extent to which oscillatory drives to muscle, believed to arise mainly from the motor cortex, are exaggerated and/or fail to react normally to peripheral stimulation in writer's cramp. We used the coherence between active forearm flexor and intrinsic hand muscles as our index of such drives before and after digital nerve stimulation of the dominant hand. The results in 8 patients with writer's cramp were compared with those in eight age- and sex-matched healthy subjects. We found no significant difference in either the strength of intermuscular coherence or its modulation by cutaneous stimulation between patients and healthy subjects during voluntary flexion of the wrist and extension-abduction of the fingers. Therefore, we were unable to provide evidence for a pervasive disturbance of oscillatory cortical motor outflow in writer's cramp.     

Increased co-activation of the upper limb muscles in writer''s cramp.

Eleven patients with writer's cramp were studied during the performance of a series of writing and non-writing tasks. Their performance in the tasks and the intensity of contraction in the flexor and extensor muscles of the fingers and elbow (recorded electromyographically) were compared with the results from a group of matched normal controls. The patients showed highly significant increases in muscle activation especially in the triceps muscle which was overactive in all but one of the tasks undertaken. Psychometric testing showed no difference between patients and controls. The results support the view that writer's cramp is a form of focal dystonia in which the disorder of motor control is not confined to writing activities.     

The DYT1 GAG deletion is infrequent in sporadic and familial writer' s cramp.

A 3-base pair (GAG) deletion in the DYT1 gene has recently been found to be responsible for most cases of early-onset primary generalized dystonia. In some cases, this mutation has been associated with writer's cramp. To determine the frequency of this mutation in a larger series of patients, we examined 44 index patients with sporadic or familial (seven patients) writer's cramp for the presence of the DYT1 GAG deletion, including eight patients with segmental dystonia involving at least one upper limb. We found the mutation in none of these index patients, which confirms that isolated writer's cramp is only in rare cases a phenotypic manifestation of this mutation, even if a positive family history of writer's cramp is present.     

Corticospinal excitability during motor imagery of a simple tonic finger movement in patients with writer's cramp.

Motor imagery (MI) is the mental rehearsal of a motor act without overt movement. Using transcranial magnetic stimulation (TMS), we tested the effect of MI on corticospinal excitability in patients with writer's cramp. In 10 patients with writer's cramp and 10 healthy controls, we applied focal TMS over each primary motor area and recorded motor evoked potentials (MEPs) from contralateral hand and arm muscles while participants imagined a tonic abduction of the index finger contralateral to the stimulated hemisphere. In healthy controls and patients, the MEP amplitude in the relaxed first dorsal interosseus muscle (FDI) showed a muscle-specific increase during MI; however, the increase was less pronounced in patients than in healthy controls. In addition, in patients but not in controls, the MEP amplitude also increased in hand and forearm muscles not involved in the imagined movement. This abnormal spread of facilitation was observed in the affected and unaffected upper limb. MI of simple hand movements is less efficient and less focussed in patients with writer's cramp than it is in normal subjects.     

Abnormal spinal interactions from hand afferents to forearm muscles in writer's cramp.

OBJECTIVE: Spinal reflexes from hand to wrist muscles were investigated in writer's cramp. METHODS: Stimulus-triggered rectified EMG averages after ulnar nerve and cutaneous stimulation, in wrist flexors and extensors during tonic contraction, were compared in 18 controls and 19 patients. RESULTS: On the patient dystonic side, ulnar-induced EMG suppression was decreased in wrist extensors, and facilitation in wrist flexors modified dependent on the dystonic wrist posture during writing. No change was found on the patient non-dystonic side. Cutaneous stimulation increased wrist flexor EMG on both sides of the patients with normal wrist posture during writing, but had no effect in controls and patients with abnormal wrist posture. CONCLUSIONS: Comparison between cutaneous and mixed nerve stimuli suggests that spindle afferents from intrinsic hand muscles may mediate patients' ulnar-induced EMG modulations. Abnormal proprioceptive control was only observed on dystonic side, while bilateral unusual cutaneous control was found in patients. Changes in spinal transmission were partly related to the dystonic wrist posture, suggesting that systems involved in sensory processing can be differentially altered in writer's cramp. SIGNIFICANCE: Changes in spinal transmission, probably related to peripheral and/or cortical inputs, might either take part in primary or adaptive mechanisms underlying writer's cramp.     

Lack of inhibitory interaction between somatosensory afferent inputs and intracortical inhibitory interneurons in focal hand dystonia.

We looked for an impaired interaction in the primary motor cortex between intracortical inhibitory circuits and circuits fed by somatosensory inputs in patients with writer's cramp. Short-interval intracortical inhibition (sICI) to wrist extensor carpi radialis muscle (ECR) was conditioned by stimulation of antagonist muscle afferents and sICI to first dorsal interosseus (FDI) muscle by homotopic cutaneous afferents stimulation. sICI was assessed at rest and during a tonic contraction of the target muscle. Eighteen patients with writer's cramp (10 having a wrist dystonic posture in flexion during writing and 8 in extension) were compared to 14 control subjects. Peripheral inputs decreased sICI in control subjects. This decrease was lost in patients in both FDI and ECR, regardless of the wrist dystonic posture. By contrast, contraction-induced depression of sICI appeared dependant on the dystonic status of the muscle: depression of sICI to ECR was abolished in patients with wrist dystonic posture in flexion, but not in patients with dystonic posture in extension, sICI even giving way to motor-evoked potential facilitation. Loss of interaction between interneurons mediating sICI and peripheral inputs probably belongs to the initial abnormalities underlying dystonia. Lack of peripherally induced sICI modulation may oppose wrist and/or hand muscles synergies.     

书写痉挛的外科治疗

目的：回顾书写痉挛的立体定向丘脑腹外侧核毁损术治疗方法及疗效。探讨书写痉挛的发生和治疗的机理。方法：运用微电极导向立体定向技术，对8例书写痉挛患者实施了丘脑腹外侧核毁损术，进行疗效分析。结果：8例患者术后书写功能即刻恢复正常，无手术并发症，1－2年的随访疗效稳定。结论：立体定向丘脑膜外侧核毁损术是治疗书写痉挛有效，安全的治疗手段，可能的治疗机制是阻断了基底节的异常爆发性电活动。     

Disturbed sensorimotor processing during control of precision grip in patients with writer's cramp.

The aim of the study was to investigate force regulation in patients with writer's cramp when performing a drawer-opening task using the precision grip. Experimental conditions included intervening load pulses and vibratory manipulations for examining grip force responses to sensory disturbances. The data revealed that grip force was increased in patients with writer's cramp compared with normal subjects, with a stronger modulation in the symptomatic compared with the asymptomatic hand. This denotes a change in force scaling capabilities and most notably for the preferred hand used in manipulative activities. Vibratory stimulation of the extrinsic hand/finger muscles resulted in an increased grip force of both hands in the patients with writer's cramp. The latter was not observed in normal subjects and supports a bilateral dysfunction in sensorimotor integration resulting from focal dystonia. In conclusion, the disturbed regulation of the precision grip during a drawer-opening task is illustrative for the inability of patients with writer's cramp to efficiently control the force output during manipulative activities.     

Abnormal plasticity of the sensorimotor cortex to slow repetitive transcranial magnetic stimulation in patients with writer's cramp.

Previous studies demonstrated functional abnormalities in the somatosensory system, including a distorted functional organization of the somatosensory cortex (S1) in patients with writer's cramp. We tested the hypothesis that these functional alterations render S1 of these patients more susceptible to the "inhibitory" effects of subthreshold 1 Hz repetitive transcranial magnetic stimulation (rTMS) given to S1. Seven patients with writer's cramp and eight healthy subjects were studied. Patients also received rTMS to the motor cortex hand area (M1). As an outcome measure, short-latency afferent inhibition (SAI) was tested. SAI was studied in the relaxed first dorsal interosseous muscle using conditioning electrical stimulation of the index finger and TMS pulses over the contralateral M1. Baseline SAI did not differ between groups. S1 but not M1 rTMS reduced SAI in patients. rTMS had no effects on SAI in healthy subjects. Because SAI is mediated predominantly at a cortical level in the sensorimotor cortex, we conclude that there is an abnormal responsiveness of this area to 1 Hz rTMS in writer's cramp, which may represent a trait toward maladaptive plasticity in the sensorimotor system in these patients.     

Bilateral mirror writing movements (mirror dystonia) in a patient with writer's cramp: functional correlates.

A recent prospective analysis on writer's cramp showed that up to 44.6% of patients in a series of 65 presented mirror dystonia, defined as involuntary movements of the resting hand, abnormal posture, tremor, and jerks occurring while writing with the opposite hand. A clinical case is presented, with videotape evidence of right-handed writer's cramp, with mirror movements elicited while writing using either hand. Functional magnetic resonance imaging studies are compared both to those of a normal patient and to those from a patient with writer's cramp but lacking mirror dystonia. Widespread bilateral activation of cortical motor areas contralateral to the mirror movements in patients with writer's cramp and mirror movements suggests, that bilateral activation of the primary motor cortex may account for the appearance of these mirror movements. Further studies need to be conducted to determine whether mirror movements in dystonic patients appear as a result of loss of intra- and/or interhemispheric cortical inhibition or are simply a consequence of the sustained effort these patients need to exert while writing using a dystonic hand.     

Usefulness of a writing device in writer's cramp

Fifteen of 20 patients with writer's cramp treated with a writing device noted an improvement in their writing ability, some quite marked. Despite this benefit, nine patients preferred to use alternate methods. In the absence of adverse effects, we suggest that trials of writing devices be the first recourse for all patients with writer's cramp requiring treatment.     

Prospective clinical study of writer's cramp.

Sixty-five consecutive patients with writer's cramp were studied prospectively to evaluate clinical and demographic features, the number of writing hours per day at dystonia onset, and the existence of trigger events. Assessment of writing and drawing was done on a standardized test using categorical scales. The importance of subjective handicap and pain, of postural and action tremor, the abnormal features of hand grip and the occurrence of mirror dystonia (dystonia occurring in the dominant hand when writing with the other hand) were studied. Thirty-two patients had simple writer's cramp, whereas the others had complex writer's cramp with several activities other than writing involved. No significant differences were seen in age of onset, legibility, pain, and handicap in these two groups. Seven patients had a family history of focal dystonia and six of them had a complex form of writer's cramp. Mirror dystonia was seen in 29 patients and in some it appeared useful to distinguish dystonic movements from secondary compensatory strategies.     

Nonlinear sensory cortex response to simultaneous tactile stimuli in writer's cramp.

Writer's cramp is a task-specific dystonia that leads to involuntary hand postures during writing. Abnormalities of sensory processing may play a pathophysiological role in this disorder. Electrophysiology studies in a monkey model of focal dystonia have revealed de-differentiation of sensory maps and the existence of single cells in hand regions of area 3b with enlarged receptive fields that extend to the surfaces of more than one digit. These changes may lead to abnormal processing of simultaneous sensory inputs. To study abnormal processing of simultaneous sensory information in adult humans with writer's cramp, we used functional magnetic resonance imaging to compare the response in primary sensory cortex with simultaneous tactile stimulation of the index and middle finger, with the response to stimulation of each finger alone. We tested five patients with writer's cramp and seven unaffected (normal) subjects. In the normal subjects, a linear combination of the activation patterns for individual finger stimulation predicts the pattern of activity for combined stimulation with 12% error. In writer's cramp patients, the linear combination predicted the combined stimulation pattern with 30% error. Results indicate a nonlinear interaction between the sensory cortical response to individual finger stimulation in writer's cramp. This altered interaction may contribute to the motor abnormalities.     

Movement-related electroencephalographic desynchronization in patients with hand cramps: evidence for motor cortical involvement in focal dystonia

We studied the dynamic changes in the amplitude of scalp electroencephalographic (EEG) oscillations to self-paced simple index finger abduction movements in patients with writer's cramp and compared them with those of normal aged-matched controls. The changes in EEG oscillations were measured in predefined frequency bands (8-10, 10-12, 12-20, and 20-30 Hz) by using the event-related desynchronization technique. Movements of the affected and unaffected hand in patients with writer's cramp showed significantly less reduction in 20- to 30-Hz power compared with controls. The differences in movement-related EEG power decline were apparent over the contralateral central and midline regions before and after electromyographic onset. Because EEG beta rhythm in the sensorimotor region likely emanates from the motor cortex and is related to ongoing muscle activity, this abnormality could be a manifestation of the abnormal motor command at the cortical level.     

Treatment of upper limb dystonia with botulinum toxin

The use of botulinum toxin A (BTX A) in upper limb dystonia is gaining increasing acceptance and it has recently been suggested that it be considered as first line treatment.(1) We have reviewed our experience since 1991 of treating 20 cases of upper limb dystonia. 14 patients had task-specific dystonias (6 simple writer's cramp, 5 dystonic writer's cramp, 3 musician's cramp) and 6 had secondary focal or segmental dystonias (4 with early cortico-basal degeneration). All patients had electromyography to both determine and guide muscle selection. Pre- and post-treatment video as well as questionnaires formed the basis for outcome assessment. Botulinum toxin therapy was clearly beneficial in about two-thirds of those with primary upper limb dystonia, a condition affecting young adults (mean onset 32.9 years). In contrast, BTX A was far less effective in secondary upper limb dystonias which occurred in the elderly (mean onset 71.7 years). Optimal treatment strategies are discussed. In conclusion, botulinum toxin is an effective form of treatment for primary upper limb dystonia; its role in late onset secondary dystonia is mainly palliative.     

Basal ganglia-premotor dysfunction during movement imagination in writer's cramp

The pathophysiology of idiopathic focal hand dystonia (writer's cramp) is characterized by deficient inhibitory basal ganglia function and altered cortical sensorimotor processing. To explore if this is already a primary finding in dystonia for internal movement simulation independent of dystonic motor output or abnormal sensory input, we investigated the neural correlates of movement imagination and observation in patients with writer's cramp. Event-related fMRI was applied during kinesthetic motor imagery of drawing simple geometric figures (imagination task) and passively observing videos of hands drawing identical figures (observation task). Compared with healthy controls, patients with writer's cramp showed deficient activation of the left primary sensorimotor cortex, mesial and left dorsal premotor cortex, bilateral putamen, and bilateral thalamus during motor imagery. No significant signal differences between both groups were found during the observation task. We conclude that internal movement simulation and planning as tested during imagination of hand movements appear to be dysfunctional in patients with writer's cramp, whereas visual signal processing and observation-induced activation are unaffected. Deficient basal ganglia-premotor activation could be a correlate of impaired basal ganglia inhibition and focusing during the selection of motor programs in dystonia. This finding seems to be an intrinsic deficit, as it is found during motor imagery in the absence of dystonic symptoms. ? 2012 Movement Disorder Society.     

Writer's cramp—A habit for reversal?

Four patients with writer's cramp were treated by nurse-therapists who used a combination of habit reversal, in vivo exposure and re-education. All four resumed normal writing activities after an average of four sessions. At follow-up 2-6 yr later, only one had relapsed, and she improved after further sessions. The brevity and simplicity of this method recommend it in the treatment of writer's cramp.     

Abnormal perception of the tonic vibration reflex in idiopathic focal dystonia

Although the pathophysiological basis of idiopathic focal dystonia (IFD) remains unclear, we recently reported abnormal perception of the tonic vibration reflex (TVR) in the biceps brachii in IFD. In this study we examined whether the abnormality affects muscles other than the biceps brachii. A 100-Hz vibration stimulating predominantly the muscle spindle afferent was transcutaneously applied to one muscle tendon of the triceps brachii, the wrist extensor and flexor muscles in 29 subjects with IFD (18 with torticollis, 9 with writer's cramp, 2 with blepharospasm) and 15 control subjects. The blindfolded subjects were instructed to copy any perceived movement with the opposite tracking arm. The elbow or wrist angle changes were quantified electronically. The TVR and subjects' perception of the TVR were evaluated by angle movements of the vibrated joint and of the tracking joint, respectively. Perception of the TVR was significantly reduced in dystonic subjects at both elbow and wrist joints, while magnitude of the TVR did not differ between the two groups. Abnormal central perception of the TVR is a feature of IFD, suggesting a widespread involvement of abnormal muscle spindle afferent processing in IFD.     

Abnormalities of spatial and temporal sensory discrimination in writer's cramp.

Clinical observations of patients with writer's cramp suggest that abnormalities of the sensory system may be a frequent finding in this disorder. Neurophysiological data from an animal model of focal dystonia have revealed cells in somatosensory cortex with enlarged and overlapping tactile receptive fields. However, psychophysical studies so far have been unable to document a clinical correlate supporting a similar enlargement of receptive fields in humans. We compared the fingertip discrimination of the orientation of fine spatial gratings between writer's cramp and control subjects and found a significant decrease in grating sensitivity in the patients, consistent with the possibility of enlarged tactile receptive fields. In addition, we duplicated previous experiments showing an abnormality of tactile temporal discrimination. The results provide psychophysical measures which may relate to the development of sensory cortical reorganization in patients with writer's cramp.