Sahana N. Kukke

Definition and Classification of Negative Motor Signs in Childhood

In this report we describe the outcome of a consensus meeting that occurred at the National Institutes of Health in Bethesda, Maryland, March 12 through 14, 2005. The meeting brought together 39 specialists from multiple clinical and research disciplines including developmental pediatrics, neurology, neurosurgery, orthopedic surgery, physical therapy, occupational therapy, physical medicine and rehabilitation, neurophysiology, muscle physiology, motor control, and biomechanics. The purpose of the meeting was to establish terminology and definitions for 4 aspects of motor disorders that occur in children: weakness, reduced selective motor control, ataxia, and deficits of praxis. The purpose of the definitions is to assist communication between clinicians, select homogeneous groups of children for clinical research trials, facilitate the development of rating scales to assess improvement or deterioration with time, and eventually to better match individual children with specific therapies. “Weakness” is defined as the inability to generate normal voluntary force in a muscle or normal voluntary torque about a joint. “Reduced selective motor control” is defined as the impaired ability to isolate the activation of muscles in a selected pattern in response to demands of a voluntary posture or movement. “Ataxia” is defined as an inability to generate a normal or expected voluntary movement trajectory that cannot be attributed to weakness or involuntary muscle activity about the affected joints. “Apraxia” is defined as an impairment in the ability to accomplish previously learned and performed complex motor actions that is not explained by ataxia, reduced selective motor control, weakness, or involuntary motor activity. “Developmental dyspraxia” is defined as a failure to have ever acquired the ability to perform age-appropriate complex motor actions that is not explained by the presence of inadequate demonstration or practice, ataxia, reduced selective motor control, weakness, or involuntary motor activity.

Abnormalities of tactile sensory function in children with dystonic and diplegic cerebral palsy.

Recent studies have shown the presence of sensory dysfunction in adults with focal dystonias. The authors hypothesize that children with secondary dystonia due to cerebral palsy may share a similar sensory dysfunction. To test this hypothesis, they evaluated tactile spatial discrimination threshold using Johnson, Van Boven, Phillips domes in 10 children with cerebral palsy and upper extremity dystonia, 8 children with diplegic cerebral palsy without involvement of the arms, and 21 unaffected children. Both patient groups had poor tactile discrimination compared with controls. The authors therefore conclude that children with secondary dystonia and diplegia due to cerebral palsy have deficits of tactile sensation that are similar to deficits seen in adults with focal dystonia. These results are the first to test the spatial discrimination threshold using Johnson, Van Boven, Phillips domes in children with cerebral palsy.

The effects of trunk stimulation on bimanual seated workspace

This study explores the effects of functional electrical stimulation (FES) of the lumbar trunk extensors on the seated posture and bimanual workspace of subjects with spinal cord injury (SCI). Four subjects with motor complete SCI with implanted intramuscular stimulating electrodes to activate the lumbar erector spinae were studied. The positions of markers on the pelvis, trunk, and hands were monitored by a motion capture system during bimanual reaching maneuvers. To define three-dimensional functional workspace boundaries, subjects swept their hands through the extremes of their range of motion without losing balance while sitting. To characterize forward reach, subjects reached to targets in the sagittal plane while carrying various masses with and without FES. Reaching trials were rated on the seven-point usability rating scale to determine effort and subject preference and change in pelvic angle with stimulation was monitored. There was a consistent change in the seated posture with FES in all subjects that resulted in significant forward or upward (6.85 cm /spl plusmn/ 2.15 cm) shifts in the workspace. Workspace volumes increased for two of the four subjects tested. FES caused significant anterior rotation of the pelvis to restore a more natural lumbar curve without a backrest (19.81/spl deg/ /spl plusmn/ 8.75/spl deg/). With a backrest, the change in posture with FES allowed individuals with SCI to reach further in the sagittal plane and carry heavier masses by shifting the trunk, allowing increased elbow extension, or a combination of the two mechanisms. Reaching with FES was consistently preferred over reaching without FES. This preliminary study is encouraging for future research on trunk stability and reaching ability with FES.

Botulinum toxin type B improves the speed of reaching in children with cerebral palsy and arm dystonia: an open-label, dose-escalation pilot study.

Seven children between 2 and 15 years of age with cerebral palsy and upper extremity dystonia were enrolled in an open-label, dose-escalation pilot clinical trial of botulinum toxin type B (Myobloc), injected into the biceps and brachioradialis muscles of 1 or both arms. The primary outcome measure was the change in maximum speed of hand movement during attempted forward reaching. Escalating doses of 12.5, 25, and 50 U/kg per muscle were injected at each of 3 visits. Reaching speed improved in response to injection, and dystonia scores on the Burke-Fahn-Marsden dystonia scale, the Unified Dystonia Rating Scale, and the Unified Parkinsons Disease Rating Scale improved. There was not a dose-related effect on efficacy. There were no serious adverse events. Two children reported transient weakness. These results support the use of botulinum toxin type B as a safe and effective treatment for upper extremity dystonia in children with cerebral palsy. Larger controlled trials are needed to confirm these results.

Induction of Motor Associative Plasticity in the Posterior Parietal Cortex–Primary Motor Network

There is anatomical and functional connectivity between the primary motor cortex (M1) and posterior parietal cortex (PPC) that plays a role in sensorimotor integration. In this study, we applied corticocortical paired-associative stimuli to ipsilateral PPC and M1 (parietal ccPAS) in healthy right-handed subjects to test if this procedure could modulate M1 excitability and PPC-M1 connectivity. One hundred and eighty paired transcranial magnetic stimuli to the PPC and M1 at an interstimulus interval (ISI) of 8 ms were delivered at 0.2 Hz. We found that parietal ccPAS in the left hemisphere increased the excitability of conditioned left M1 assessed by motor evoked potentials (MEPs) and the input-output curve. Motor behavior assessed by the Purdue pegboard task was unchanged compared with controls. At baseline, conditioning stimuli over the left PPC potentiated MEPs from left M1 when ISI was 8 ms. This interaction significantly attenuated at 60 min after left parietal ccPAS. Additional experiments showed that parietal ccPAS induced plasticity was timing-dependent, was absent if ISI was 100 ms, and could also be seen in the right hemisphere. Our results suggest that parietal ccPAS can modulate M1 excitability and PPC-M1 connectivity and is a new approach to modify motor excitability and sensorimotor interaction.

Cortical silent period duration and its implications for surround inhibition of a hand muscle

Surround inhibition is a neural mechanism that assists in the focusing of excitatory drive to muscles responsible for a given movement (agonist muscles) by suppressing unwanted activity in muscles not relevant to the movement (surround muscles). The purpose of the study was to determine the contribution of γ‐aminobutyric acidB receptor‐mediated intracortical inhibition, as assessed by the cortical silent period (CSP), to the generation of surround inhibition in the motor system. Eight healthy adults (five women and three men, 29.8 ± 9 years) performed isometric contractions with the abductor digiti minimi (ADM) muscle in separate conditions with and without an index finger flexion movement. The ADM motor evoked potential amplitude and CSP duration elicited by transcranial magnetic stimulation were compared between a control condition in which the ADM was activated independently and during conditions involving three phases (pre‐motor, phasic, and tonic) of the index finger flexion movement. The motor evoked potential amplitude of the ADM was greater during the control condition compared with the phasic condition. Thus, the presence of surround inhibition was confirmed in the present study. Most critically, the CSP duration of the ADM decreased during the phasic stage of finger flexion compared with the control condition, which indicated a reduction of this type of intracortical inhibition during the phasic condition. These findings indicate that γ‐aminobutyric acidB receptor‐mediated intracortical inhibition, as measured by the duration of the CSP, does not contribute to the generation of surround inhibition in hand muscles.

Efficient and reliable characterization of the corticospinal system using transcranial magnetic stimulation.

Purpose: The purpose of this study is to develop a method to reliably characterize multiple features of the corticospinal system in a more efficient manner than typically done in transcranial magnetic stimulation studies. Methods: Forty transcranial magnetic stimulation pulses of varying intensity were given over the first dorsal interosseous motor hot spot in 10 healthy adults. The first dorsal interosseous motor-evoked potential size was recorded during rest and activation to create recruitment curves. The Boltzmann sigmoidal function was fit to the data, and parameters relating to maximal motor-evoked potential size, curve slope, and stimulus intensity leading to half-maximal motor-evoked potential size were computed from the curve fit. Results: Good to excellent test–retest reliability was found for all corticospinal parameters at rest and during activation with 40 transcranial magnetic stimulation pulses. Conclusions: Through the use of curve fitting, important features of the corticospinal system can be determined with fewer stimuli than typically used for the same information. Determining the recruitment curve provides a basis to understand the state of the corticospinal system and select subject-specific parameters for transcranial magnetic stimulation testing quickly and without unnecessary exposure to magnetic stimulation. This method can be useful in individuals who have difficulty in maintaining stillness, including children and patients with motor disorders.

Poor Penmanship in Children Correlates With Abnormal Rhythmic Tapping: A Broad Functional Temporal Impairment

Timing is crucial for proficient motor tasks; temporal impairments may lead to dysfunctional motor activities. Although much research has been dedicated to the study of movement timing, clinical examination often overlooks temporal impairment of motor activity. The authors hypothesize that some children have a global temporal impairment leading to dysfunctional motor skills. This article checks whether temporal abnormalities detected on a simple tapping task correlate with temporal dysfunction during complex motor skills such as handwriting. Twenty-three school-aged children, 8-14 years (11.1 ± 1.3 years), underwent tests to assess finger tapping and cursive handwriting. Handwriting samples were rated by experienced teachers. Children with abnormal tapping had lower handwriting rating scores. Temporal features were similar in both tasks; variability on the tapping test correlated with handwriting variability. Temporal variability was not significantly higher for children with poor penmanship as a whole but rather specific to the subgroup of children with a tapping abnormality. Poor penmanship could be attributed in certain children to global temporal impairment reflected as variable finger tapping and handwriting. Evaluation of dysfunctional motor performance should include temporal aspects, and further studies are needed to better delineate and address treatment of “dysrhythmia.”

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.

Contributors to excess antagonist activity during movement in children with secondary dystonia due to cerebral palsy

Children with secondary dystonia due to cerebral palsy exhibit abnormal upper extremity postures and slow voluntary movement. However, the interaction between abnormal postures and abnormal movement in dystonia is still unclear. Some mechanisms by which postures are maintained in dystonia include stretch reflexes, overflow of muscle activation to other muscles, and direct coactivation of antagonist muscles. This study explored the independent contributions of each of these postural mechanisms to abnormal biceps brachii (antagonist) activity during elbow extension, which slows movement. A linear model of biceps activation as a function of velocity-dependent reflexes, triceps-dependent overflow, and direct drive to the biceps was fitted to experimental data from 11 children and young adults with secondary dystonia due to cerebral palsy and 11 age-matched control subjects. Subjects performed elbow extension movements against each of four levels of resistance without perturbations or in each of two perturbation conditions. Results show that biceps activity in children with dystonia consists of significant contributions of reflex activation, overflow from triceps, and direct muscular drive. Additionally, stretch reflexes during movement are shown to be elevated at three latencies after stretch. These findings suggest that there are postural mechanisms involved in stabilizing the elbow along its slow trajectory during movement and provide a quantitative basis for the selection of treatments targeting specific impairments in children with secondary dystonia due to cerebral palsy.