Hypertonia in childhood secondary dystonia due to cerebral palsy is associated with reflex muscle activation

It is often assumed that co‐contraction of antagonist muscles is responsible for increased resistance to passive movement in hypertonic dystonia. Although co‐contraction may certainly contribute to hypertonia in some patients, the role of reflex activation has never been investigated. We measured joint torque and surface electromyographic activity during passive flexion and extension movements of the elbow in 8 children with hypertonic arm dystonia due to dyskinetic cerebral palsy. In all cases, we found significant phasic electromyographic activity in the lengthening muscle, consistent with reflex activity. By correlating activation with position or velocity of the limb, we determined that some children exhibit position‐dependent activation, some exhibit velocity‐dependent activation, and some exhibit a mixed pattern of activation. We conclude that involuntary or reflex muscle activation in response to stretch may be a significant contributor to increased tone in hypertonic dystonia, and we conjecture that this activation may be more important than co‐contraction for determining the resistance to passive movement. © 2009 Movement Disorder Society     

The relationship of voluntary movement to spasticity in the upper motor neuron syndrome

Hyperactive strethch reflexes in the upper motor neuron (UMN) syndrome are frequently cited as an impediment to volitional movement. The assumption is that neural or mechanical activity of the hyperactive antagonist interferes with agonist function. The validity of this assumption was examined by evaluating quantitative and qualitative relationships between stretch reflexes and voluntary movement. Sixteen patients with chronic UMN symptoms and 8 normal volunteers were tested. Joint position and integrated electromyograms from primary flexors and extensors were recorded. Quantitated values of (1) reflex response to controlled passive motion by an automated system, (2) a maximal voluntary isometric contraction, and (3) the time required for ten voluntary rapid repetitive movements (RRM) of alternating elbow flexion and extension were obtained. Passive movement elicited tonic reflexes, which predominated during muscle stretch in patients and during muscle shortening in the volunteers. Ratios of the EMG activity elicited during stretch, shortening, and isometric activity were used as measures of spasticity and were compared with the time for RRM. A positive correlation between elbow flexor spasticity and the time for RRM was shown. Qualitative analysis of the EMG activity during voluntary isotonic movement, however, showed that primary impairment of movement is not due to antagonist stretch reflexes, but rather to limited and prolonged recruitment of agonist contraction and delayed cessation of agonist contraction at the termination of movement.     

Deficits in the coordination of agonist and antagonist muscles in stroke patients: implications for normal motor control

Movement impairments about a single joint in stroke patients may be related to deficits in the central regulation of stretch reflex (SR) thresholds of agonist and antagonist muscles. One boundary of the SR threshold range for elbow flexor and extensor muscles was measured in hemiparetic subjects by analysing electromyographic activity during stretching of relaxed muscles at seven different velocities. For each velocity, dynamic SR thresholds were measured as angles at which electromyographic activity appeared. These data were used to determine the sensitivity of the threshold to velocity and the static SR thresholds for flexors and extensors. In contrast to relaxed muscles in healthy subjects, static flexor and extensor thresholds lay within the physiological range in 11/12 and 4/12 subjects, respectively. This implies that, in the range between the static SR threshold and one of the physiological joint limits, relaxation of the muscle was impossible. Subjects then made slow movements against different loads to determine their ranges of active movement. Maximal flexor and extensor torques were lower in hemiparetic subjects throughout the angular range. In some subjects, ranges were found in which no active torque could be produced in either extensor or both muscle groups. These ranges were related to the boundary values of SR thresholds found during passive muscle stretch. The range in which reciprocally organized agonist and antagonist muscle activity could be generated was limited in all but one subject. When attempting to produce torque from positions outside their measured range of movement, excessive muscle coactivation occurred, typically producing no or paradoxical motion in the opposite direction. Results suggest a relationship between spasticity measured at rest and the movement deficit in stroke by demonstrating a link between motor deficits and control deficits in the central regulation of individual SR thresholds.     

Torque variations during repeated passive isokinetic movements of the knee in subjects with Parkinson's disease and healthy control subjects

The purpose of this study was to quantify response variations during isokinetic passive movements of the knee in subjects with Parkinson's disease. Parkinsonian patients demonstrated a greater decrease of resistive torque compared to healthy control subjects, particularly in tests at higher velocities and during knee flexion movements. Responses were influenced by electromyographic activity in stretched and shortened muscle groups and also by mechanical factors. The results indicate that repetition of movements needs to be taken into account when measuring hypertonia in parkinsonian subjects.     

Disturbances in human arm movement trajectory due to mild cerebellar dysfunction.

The temporal structure of arm movements was studied in nine cerebellar patients with mild impairment of the upper limbs and in six age-matched control subjects. The experimental paradigm consisted of visually guided, step tracking movements about the elbow. Movements ranged from 10 degrees to 70 degrees in amplitude and were made under different instructions (fast, fast/accurate, accurate). As in normal subjects, cerebellar patients were able to scale peak velocity with movement amplitude. This relationship was highly linear under all instruction conditions. Similar relationships existed between movement duration and amplitude. In contrast to normal subjects who produced movements with nearly symmetric velocity profiles, movements made by cerebellar patients were characterised by short acceleration and long deceleration durations. The degree of asymmetry was directly related to movement duration but was unaffected by movement peak velocity. Acceleration durations did not increase beyond 300 ms even in movements lasting up to 1s. These findings demonstrate that, despite little or no obvious impairment of the limb during routine examination, the temporal structure of voluntary movements in cerebellar patients is clearly disturbed. This supports the view that the production of an optimal movement trajectory is under cerebellar influence.     

Spastic movement disorder: impaired reflex function and altered muscle mechanics

In clinical practice, signs of exaggerated tendon tap reflexes associated with muscle hypertonia are generally thought to be responsible for spastic movement disorders. Most antispastic treatments are, therefore, directed at the reduction of reflex activity. In recent years, however, researchers have noticed a discrepancy between spasticity as measured in the clinic and functional spastic movement disorders, which is primarily due to the different roles of reflexes in passive and active states, respectively. We now know that central motor lesions are associated with loss of supraspinal drive and defective use of afferent input with impaired behaviour of short-latency and long-latency reflexes. These changes lead to paresis and maladaptation of the movement pattern. Secondary changes in mechanical muscle fibre, collagen tissue, and tendon properties (eg, loss of sarcomeres, subclinical contractures) result in spastic muscle tone, which in part compensates for paresis and allows functional movements on a simpler level of organisation. Antispastic drugs can accentuate paresis and therefore should be applied with caution in mobile patients.     

Fast voluntary neck movements in patients with cervical dystonia: a kinematic study before and after therapy with botulinum toxin type A.

OBJECTIVE: To study fast voluntary neck movements in patients with cervical dystonia (CD) before and after therapy with botulinum toxin type-A (BTX-A). METHODS: A selected sample of 15 patients with CD (with prevalent torticollis) and 13 age-matched control subjects performed both right and left rotational, and flexion and extension neck movements as fast as possible. Movements were recorded with a motion analysis system (SMART, BTS). Movement time, angular amplitude, and peak angular velocity were analyzed. In patients, rotational neck movements were pooled as "pro-dystonic" (toward the dystonic side) and "anti-dystonic" (toward the non-dystonic side). Results obtained in patients before BTX-A treatment were compared with those of control subjects. The effect of BTX-A treatment was evaluated by comparing movement performance before and after treatment. RESULTS: Before receiving BTX-A, patients performed pro- and anti-dystonic movements with lower peak angular velocity than control subjects. Pro-dystonic movements had a reduced angular amplitude. Anti-dystonic movements showed an abnormally long movement time. Flexion and extension movements required longer movement times, but the other kinematic variables were normal. After BTX-A injections, pro-dystonic movement amplitude and anti-dystonic movement peak angular velocity increased, whereas flexion and extension movements remained unchanged. CONCLUSIONS: Before BTX-A injection patients with CD perform fast voluntary neck movements abnormally and BTX-A injections improved their peak velocity and amplitude. SIGNIFICANCE: Kinematic studies can detect specific neck movement disturbance in patients with CD, and can quantify both the severity of clinical picture and the effect of BTX-A injections in these patients.     

Pathophysiological mechanisms in cerebral palsy.

To investigate some of the pathophysiological mechanisms in cerebral palsy, surface electromyograms (EMG) were recorded from pairs of flexor/extensor muscles during both voluntary and passive flexion/extension of upper and lower limbs of 20 patients. Elbow, knee, or ankle joint angles were measured simultaneously, as well as the force required to flex/extend the limbs passively at frequencies of 0.1--1.0 Hz. In addition, single motor units were recorded from the first dorsal interosseous muscles of six of the patients. Almost all patients showed resistance to passive movements (hypertonia). This hypertonia did not necessarily impair voluntary flexion/extension movements if alternating EMG activity was maintained in at least one of the pairs of flexor/extensor muscles involved in the movement. In six severly involved patients, there was a complete breakdown in the reciprocal relationship between reciprocally acting pairs of flexor/extensor motoneurones, which resulted in synchronous activation (co-contractions) of flexor/extensor muscles during both voluntary and passive movements. In these patients the hyperactive segmental reflex added to the disabling effects of co-contractions during voluntary movements. Single motor units recorded from patients with dystonic movements were recruited with variable delays (2--10 s) and usually discharged intermittently at high frequencies (60--120/s). This abnormla motor unit discharge pattern may relate to pathology of the basal ganglia.     

Neck movement speed in cervical dystonia

Clinical scales of patients with cervical dystonia do not rate neck movement velocity. We prospectively measured range of neck movements and movement velocities in 35 consecutive patients with cervical dystonia (CD) and 29 normal controls. Reduction of peak velocities in patients with CD was the most robust abnormality and was correlated to TWSTRS. Coupled movements out of attempted movement plane were increased in the patient group. Movement range was moderately though significantly reduced. We conclude that slowing of voluntary neck movements is a frequent and hitherto unrecognized feature in CD. © 2009 Movement Disorder Society     

Interlimb coordination in Parkinson's disease.

This study examined the degree to which Parkinson's disease (PD) patients could "spatially link" the upper limbs to facilitate the performance of bimanual simultaneous movements. Six right-handed PD patients, and seven normal age- and sex-matched controls performed three different tasks: (a) an isotonic elbow flexion as rapidly as possible through an angle of 30 degrees; (b) an isometric contraction of the flexor muscles at the elbow joint to 40% and 60% of maximal volitional force (MVF) for a period of 5 s; (c) an isometric contraction for 2.5 s with one limb, then simultaneously performing an isotonic flexion with the contralateral limb while maintaining the isometric contraction for 2.5 s more. As expected, PD patients were significantly slower in performing the isotonic movement and produced lower peak velocities than the controls. More importantly, the two groups were differentially affected during the bimanual condition. In normals, movement time decreased and peak velocity increased in the bimanual condition. In contrast, PD patients showed increased movement times and sometimes decreased peak velocities in the bimanual condition. The results suggest that normal subjects utilize bilateral outflow to symmetrical muscle groups to synchronize the two limbs in the bimanual task, whereas PD patients dissociate the two limbs.     

Spatial zones for muscle coactivation and the control of postural stability

It is hypothesized that, depending on the motor task, the angular range of a joint may be subdivided into zones in which agonist and antagonist muscles are coactive, only one group of muscles is active or neither group is active. It is further hypothesized that central commands may change the size and location of these spatial zones. We investigated whether spatial zones are used by the nervous system and how they may be changed to provide postural stability of the elbow. We compared responses to sudden unloading of the elbow flexors in neurologically normal subjects with those in patients with postural control deficits due to unilateral hemispheric and/or subcortical lesions. By studying responses in patients, we sought to determine whether the specification of zones of agonist/antagonist muscle coactivation (“coactivation zones”) may be essential for postural stability. At an initial elbow angle (130°; full extension is 180°), flexors were pre-activated by compensating an initial load which was equal to approximately 30% of the subject's maximal isometric voluntary contraction effort. Subjects were instructed not to correct the arm displacement elicited by a sudden decrease in the load. Data from 10 trials were collected at each of 4–6 final load levels (separated by 1.5–2 Nm) in order to map out the relationship between torque and angle in each subject. The procedure was repeated from a more flexed initial position of the elbow (100°). EMG activity from two elbow flexors and two elbow extensors, as well as torque, velocity and joint position were recorded. Healthy control subjects and patients with mild clinical symptoms had coactivation zones or small silent zones around the final positions established after unloading. In these subjects, final positions of the limb were stable. Voluntary movement, i.e., transition of the limb from one initial position to another, was associated with a change in the location of the zone in articular space. The presence of large silent zones in patients with moderate or severe symptoms was correlated with postural instability and oscillations about the final position of the arm after unloading. The comparison of results from healthy and hemiparetic subjects implies that the central specification of the size and the location of a coactivation zone may be fundamental for the control of posture and movement.     

Voluntary ankle flexor activity and adaptive coactivation gain is decreased by spasticity during subacute spinal cord injury

Although spasticity has been defined as an increase in velocity-dependent stretch reflexes and muscle hypertonia during passive movement, the measurement of flexor muscle paresis may better characterize the negative impact of this syndrome on residual motor function following incomplete spinal cord injury (iSCI). In this longitudinal study Tibialis Anterior (TA) muscle paresis produced by a loss in maximal voluntary contraction during dorsiflexion and ankle flexor muscle coactivation during ramp-and-hold controlled plantarflexion was measured in ten patients during subacute iSCI. Tibialis Anterior activity was measured at approximately two-week intervals between 3-5 months following iSCI in subjects with or without spasticity, characterized by lower-limb muscle hypertonia and/or involuntary spasms. Following iSCI, maximal voluntary contraction ankle flexor activity was lower than that recorded from healthy subjects, and was further attenuated by the presence of spasticity. Furthermore the initially high percentage value of TA coactivation increased at 75% but not at 25% maximal voluntary torque (MVT), reflected by an increase in TA coactivation gain (75%/25% MVT) from 2.5 ± 0.4 to 7.5 ± 1.9, well above the control level of 2.9 ± 0.2. In contrast contraction-dependent TA coactivation gain decreased from 2.4 ± 0.3 to 1.4 ± 0.1 during spasticity. In conclusion the adaptive increase in TA coactivation gain observed in this pilot study during subacute iSCI was also sensitive to the presence of spasticity. The successful early diagnosis and treatment of spasticity would be expected to further preserve and promote adaptive motor function during subacute iSCI neurorehabilitation.     

The perception of passive motion in Parkinson's disease

Abstract The perception of limb motion is a kinaesthetic property that is essential for voluntary motor control. This study examined the ability of patients with Parkinson's disease (PD) to detect the velocity of a passively moved limb. Eight patients with mild to moderate PD and eight age-matched healthy controls participated. They placed their forearm on a padded splint of a passive motion apparatus, which horizontally extended or flexed the elbow joint at velocities between 1.65 and 0.075°/s (in steps of 0.15°/s). Passive movement persisted until subjects detected arm motion and pressed a trigger held in the hand of their non-tested arm. Time until detection and associated arm displacement were recorded and subsequently adjusted for each subject's reaction time. We found that PD patients needed significantly larger limb displacements before they could judge the presence of passive motion. With decreasing passive motion velocity the detection time increased exponentially in both groups. Yet, the mean detection times of the PD group were 92–166% higher than in the control group for each of the 12 tested velocity conditions. Five of the eight patients were on Parkinsonian medication when tested. Yet, the degree of impairment in the PD group did not correlate significantly with the patients' levodopa equivalent dosage. Our results demonstrate that PD patients were impaired in the detection of passive forearm movements. This study complements a growing body of evidence indicating that various aspects of kinaesthesis (position sense, weight perception, passive motion sense) are affected even at early stages of PD. The impaired processing of proprioceptive signals likely contributes to motor symptoms in PD.     

Proprioceptive regulation of voluntary ankle movements, demonstrated using muscle vibration, is impaired by Parkinson''s disease

OBJECTIVE: To test the hypothesis that the proprioceptive regulation of voluntary movement is disturbed by Parkinson's disease, the effects of experimental stimulation of proprioceptors, using muscle vibration, on the trajectories of voluntary dorsiflexion movements of the ankle joint were compared between parkinsonian and control subjects. METHODS: Twenty one patients with Parkinson's disease, on routine medication (levodopa in all but one), and an equal number of age matched, neurologically intact controls, were trained initially to make reproducible ankle dorsiflexion movements (20 degrees amplitude with a velocity of 9.7 degrees /s) following a visual "go" cue while movement trajectories were recorded goniometrically. During 50% of the experimental trials, vibration (105 Hz; 0.7 mm peak to peak) was applied to the Achilles tendon during the ankle movement to stimulate antagonist muscle spindles; vibrated and non-vibrated trials were interspersed randomly. Subjects' performance was assessed by measuring end point position-that is, the ankle angle attained 2 seconds after the visual "go" cue, from averaged (20 trials) trajectories. RESULTS: Statistical analysis of the end point amplitudes of movement showed that, whereas the amplitudes of non-vibrated movements did not differ significantly between patients with Parkinson's disease and controls, antagonist muscle vibration produced a highly significant reduction in the amplitudes of ankle dorsiflexion movements in both the patient and control groups. However, the extent of vibration induced undershooting produced in the patients with Parkinson's disease was significantly less than that in the controls; the mean vibrated/non-vibrated ratios were 0.86 and 0.54 for, respectively, the patient and control groups. CONCLUSIONS: The present finding of a reduction of vibration induced ankle movement errors in parkinsonian patients resembles qualitatively previous observations of wrist movements, and suggests that Parkinson's disease may produce a general impairment of proprioceptive guidance.     

Recovery of elbow function in voluntary positioning of the hand following hemiplegia due to stroke.

Elbow movement during voluntary positioning of the hand (with the arm supported against gravity) is described in a longitudinal study of five patients recovering from hemiplegia due to stroke. Over a twelve month period, four of the patients improved their speed of movement, three exhibiting slightly better recovery of elbow extension, one of flexion. In some instances co-contraction of the elbow agonist and antagonist (measured just before the onset of movement) decreased with time after stroke. The effects of contrasting movements at the shoulder on elbow movement were also studied. Estimates of recovery were generally similar whether patients kept the shoulder still or made movements that were synergic or counter-synergic to those of the elbow.     

Reciprocal change of motor-evoked potentials preceding voluntary movement in humans

Reciprocal change of motor-evoked potentials (MEPs) recorded from the agonist and antagonist muscles of the forearm was studied in 10 normal subjects in whom transcranial magnetic stimulation (TMS) was applied to the hand motor area before voluntary wrist movements. MEP recorded from the agonist muscles, that is, radial extensor muscles for wrist extension and ulnar flexor muscle for wrist flexion, were gradually facilitated with shortening of the interval between the magnetic stimulation and the voluntary muscle contraction. In contrast, MEP recorded from the antagonist muscles, that is, ulnar flexor muscle for wrist extension and radial extensor muscles for wrist flexion, were gradually suppressed as the interval shortened. The reciprocal change of MEP was recognized when TMS was applied within 60 ms prior to the voluntary movements. The present data confirmed that reciprocal change of MEP was recognized before voluntary movements; they further suggest that cortically originated reciprocal control of the corticospinal pathway may exist and that it may be generated just before the voluntary movement. © 1996 John Wiley & Sons, Inc.     

Changes in cerebral blood flow induced by passive and active elbow and hand movements

Transcranial Doppler ultrasonography (TCD) has been widely used to obtain information about changes in cerebral perfusion during monitor activity after stroke. This type of application is greatly limited when severe motor deficits are presnet that impede the performance of an active motor task. In this study, we explored the effect of performing passive arm movements on cerebral perfusion. Twenty healthy subjects were investigated. A bilateral TCD monitoring of the middle cerebral artery (MCA) flow velocity was performed during the following experimental conditions: 1-min of active and passive flexion extension elbow movement and 1-min of active and passive dorsal extension hand movement. Each task was performed with both left and right arms. The percentage increase in flow velocity from rest to task performance was calculated. Each task produced a significantly greater increase in mean flow velocity in the contralateral MCA with respect to the ipsilateral. When comparing the effect of passive and active tasks, no significant difference in mean flow velocity changes recorded in the ipsilateral and the contralateral MCA was detected regarding either elbow or hand movements. These findings demonstrate the possibility of obtaining information about changes in hemispheric cerebral perfusion during passive movements involving elbow and hand. This type of application deserves further attention in the study of cerebral functional changes following cerebral lesions. Received: 30 May 2000 / Accepted: 24 July 2000     

Cerebral evoked potentials and somatosensory perception

In normal subjects, somatosensory evoked potentials (SEPs) were produced by increases or decreases of the load on the biceps muscle during voluntary contraction. The stimuli lasted only 20 msec and caused less than 2 degrees of elbow flexion or extension. When the stimulus was applied during voluntary movement of the elbow, the SEP was attenuated, and the subject was less able to discriminate between loading and unloading pulses. In each of eight subjects, there was a positive correlation between the percentage of correct responses and the size of the SEP. The measurement of both SEPs and perceptual accuracy under various test conditions provides a refined technique for studying the relations between electrical events and sensory processes.     

Flexor and extensor muscle tone evaluated using the quantitative pendulum test in stroke and parkinsonian patients

The aim of this study was to evaluate the flexor and extensor muscle tone of the upper limbs in patients with spasticity or rigidity and to investigate the difference in hypertonia between spasticity and rigidity. The two experimental groups consisted of stroke patients and parkinsonian patients. The control group consisted of age and sex-matched normal subjects. Quantitative upper limb pendulum tests starting from both flexed and extended joint positions were conducted. System identification with a simple linear model was performed and model parameters were derived. The differences between the three groups and two starting positions were investigated by these model parameters and tested by two-way analysis of variance. In total, 57 subjects were recruited, including 22 controls, 14 stroke patients and 21 parkinsonian patients. While stiffness coefficient showed no difference among groups, the number of swings, relaxation index and damping coefficient showed changes suggesting significant hypertonia in the two patient groups. There was no difference between these two patient groups. The test starting from the extended position constantly manifested higher muscle tone in all three groups. In conclusion, the hypertonia of parkinsonian and stroke patients could not be differentiated by the modified pendulum test; the elbow extensors showed a higher muscle tone in both control and patient groups; and hypertonia of both parkinsonian and stroke patients is velocity dependent.