Longitudinal sliding of the median nerve in patients with non-specific arm pain

In patients with non-specific arm pain (NSAP; also known as repetitive strain injury), there are clinical signs of altered median nerve sliding. It is possible that a restriction along the nerve course will lead to abnormal increases in local strain during limb movements, possibly contributing to symptoms. The present study uses ultrasound imaging to examine median nerve sliding through the proximal and distal nerve segments in 18 NSAP patients. Longitudinal nerve sliding was measured during metacarpophalangeal, wrist and elbow movements. During elbow movements, the angle of elbow extension at which the nerve begins to move was determined, since this was expected to decrease with a restriction through the shoulder. The results from this study were compared with previously reported data. Nerve movements ranged from 1.26 to 4.73 mm in patients compared with 1.43-5.57 mm in controls. There was no significant difference in nerve sliding (p>0.05) or in the angle of elbow extension at which the nerve began to move (mean=53.4 degrees in patients, 52.0 degrees in controls; p>0.05). In summary, restriction of median nerve sliding is unlikely to play a major role in NSAP. Therefore, painful responses during limb movements which tension the nerve are unlikely to result from abnormal increases in nerve strain.

Decoding individuated finger movements using volume-constrained neuronal ensembles in the M1 hand area

Individuated finger and wrist movements can be decoded using random subpopulations of neurons that are widely distributed in the primary motor (M1) hand area. This work investigates 1) whether it is possible to decode dexterous finger movements using spatially-constrained volumes of neurons as typically recorded from a microelectrode array; and 2) whether decoding accuracy differs due to the configuration or location of the array within the M1 hand area. Single-unit activities were sequentially recorded from task-related neurons in two rhesus monkeys as they performed individuated movements of the fingers and the wrist. Simultaneous neuronal ensembles were simulated by constraining these activities to the recording field dimensions of conventional microelectrode array architectures. Artificial neural network (ANN) based filters were able to decode individuated finger movements with greater than 90% accuracy for the majority of movement types, using as few as 20 neurons from these ensemble activities. Furthermore, for the large majority of cases there were no significant differences (p < 0.01) in decoding accuracy as a function of the location of the recording volume. The results suggest that a brain-machine interface (BMI) for dexterous control of individuated fingers and the wrist can be implemented using microelectrode arrays placed broadly in the M1 hand area.

Monkey primary somatosensory cortical activity during the early reaction time period differs with cues that guide movements

Vibration-related neurons in monkey primary somatosensory cortex (SI) discharge rhythmically when vibratory stimuli are presented. It remains unclear how functional information carried by vibratory inputs is coded in rhythmic neuronal activity. In the present study, we compared neuronal activity during wrist movements in response to two sets of cues. In the first, movements were guided by vibratory cue only (VIB trials). In the second, movements were guided by simultaneous presentation of both vibratory and visual cues (COM trials). SI neurons were recorded extracellularly during both wrist extensions and flexions. Neuronal activity during the instructed delay period (IDP) and the early reaction time period (RTP) were analyzed. A total of 96 cases from 48 neurons (each neuron contributed two cases, one each for extension and flexion) showed significant vibration entrainment during the early RTPs, as determined by circular statistics (Rayleigh test). Of these, 50 cases had cutaneous (CUTA) and 46 had deep (DEEP) receptive fields. The CUTA neurons showed lower firing rates during the IDPs and greater firing rate changes during the early RTPs when compared with the DEEP neurons. The CUTA neurons also demonstrated decreases in activity entrainment during VIB trials when compared with COM trials. For the DEEP neurons, the difference of entrainment between VIB and COM trials was not statistically significant. The results suggest that somatic vibratory input is coded by both the firing rate and the activity entrainment of the CUTA neurons in SI. The results also suggest that when vibratory inputs are required for successful task completion, the activity of the CUTA neurons increases but the entrainment degrades. The DEEP neurons may be tuned before movement initiation for processing information encoded by proprioceptive afferents.

Management and functional outcomes of combined injuries of flexor tendons, nerves, and vessels at the wrist

A retrospective review of 42 patients with spaghetti wrist lacerations operated on by the author between June 1997 and May 2005 was completed. A total of 31 males and 11 females, average age of 17.1 years (range, 2-40 years), sustained spaghetti wrist injuries. The most frequent mechanisms of injury were accidental glass lacerations (55%), knife wounds (24%), and electrical saw injuries (11%). An average of 9.16 structures was injured, including 6.95 tendons, 1.4 nerves, and 0.8 arteries. The most frequently injured structures were median nerve (83%), flexor digitorum superficialis 2-4 tendons (81%), flexor digitorum profundus 2-4 tendons (66%), ulnar nerve and ulnar artery (57%), and flexor pollicis longus (40%). Combined flexor carpi ulnaris, ulnar nerve, and ulnar artery (ulnar triad) injuries occurred in 31%, while combined median nerve, palmaris longus, and flexor carpi radialis injuries (radial triad) occurred in 43%. Simultaneous injuries of both median and ulnar nerves occurred in 40.5%. Simultaneous injuries of both ulnar and radial arteries occurred in 14%. Neither artery was injured in 30.9%. Follow-up has ranged from 1 to 8 years, with an average of 46 months. Only four patients have been completely lost to follow-up. Range of motion of all involved digits (tendon function) was excellent in 34 patients, good in 3 patients, and poor in only 1 patient. Opposition was excellent in 31 patients, good in 5 patients, and poor in 2 patients. Intrinsic muscle recovery was subjectively reported to be excellent in 29 patients, good in 7, and fair to poor in 2 patients. Minor deformity (partial clawing) was reported in 4 patients and 1 patient has major deformity (total clawing). Sensory recovery was reported, excellent in 32 patients, good in 5 patients, and fair in only 1 patient.

[Guideline 'Diagnosis and treatment of carpal tunnel syndrome']

--Carpal tunnel syndrome (CTS) is the most frequently encountered peripheral nerve entrapment: about 10% of adult women and less than 1% of adult men in the Netherlands have a clinically and electrophysiologically confirmed CTS. --All medical and paramedical disciplines involved in the diagnosis and treatment of CTS in the Netherlands contributed to the development of a guideline for the diagnosis and treatment ofCTS. --Clinical diagnosis of CTS is based on a history of nocturnal pins and needles, numbeness and/or pain in the median nerve innervated area of the fingers and hand, which often causes the patient to awake. --Provocative tests do not contribute to the clinical diagnosis of CTS. --If invasive therapy is considered, such as corticosteroid injection or surgery, the clinical diagnosis must be confirmed by abnormal findings in electrophysiological tests. --Ultrasound or MRI of the wrist may be of diagnostic value when structural abnormalities in the carpal tunnel are suspected. Given the special expertise needed for ultrasound testing and the limited availability of MRI for CTS diagnostic purposes, these methods are not the first preference. --Depending on the degree of impact on daily functioning, treatment for CTS may be expectative, conservative (wrist splint or local steroid injections) or surgical (endoscopic or open techniques). --If CTS does not restrict daily functioning, adjustment of the working conditions will do. --Furthermore measures aimed at CTS prevention and treatment of an already existing work-related CTS are discussed.

Autonomic nervous system response to vibrating and electrical stimuli on the forearm and wrist

In today's operating rooms, anesthesiologists use physiological data monitoring systems with visual and auditory cues to receive patient information. The efficacy of these visual-audio systems is limited by the human limitations of these modalities. Previous studies have shown the potential use of a complementary, or alternate, patient data monitoring technology utilizing another psychophysically relevant modality: the sense of touch via vibro-tactile or electro-tactile stimulation. In this paper, we describe an experiment designed to determine whether the specific type and/or location of such a tactile stimulation device on the arm affects the autonomic nervous system response. In our study, each of 10 participants tested a vibro-tactile display on the forearm (VF), a vibro-tactile display on the wrist (VW), and an electro-tactile display on the forearm (EF) in random order. Using the LifeShirt, system, electrocardiogram (ECG), respiratory rate (Br), tidal volume (Vt) data were collected. Results showed a higher value of the heart rate and heart rate variability (HRV) when using the VF compared to the VW and EF. We also found that the HRV response for the three tactile prototypes was correlated with the accuracy of tactile pattern identification.

Cerebral activation patterns related to initiation and inhibition of hand movement

Sequential ordering of purposeful movements includes distinct transitions between muscle contraction and relaxation. To explore cerebral activation patterns underlying such movement initiation and inhibition, we applied functional magnetic resonance imaging to test the effects of (1) ballistic movement (dominated by initiation), (2) movement with stepwise interruption (dominated by inhibition) and (3) smooth movements. Right-hand movements were performed by 21 healthy participants. In the basal ganglia, ballistic movements evoked putamen activation, indicating its specific contribution to initiation. Stepwise interrupted movement induced increased activation of the caudate nucleus, globus pallidus and subthalamic nucleus whereas, at the cortical level, supplementary motor area activation increased. This indicates a specific basal ganglia-thalamocortical circuit involved in motor inhibition.

Improving functional magnetic resonance imaging motor studies through simultaneous electromyography recordings

Specially designed optoelectronic and data postprocessing methods are described that permit electromyography (EMG) of muscle activity simultaneous with functional MRI (fMRI). Hardware characterization and validation included simultaneous EMG and event-related fMRI in 17 healthy participants during either ankle (n = 12), index finger (n = 3), or wrist (n = 2) contractions cued by visual stimuli. Principal component analysis (PCA) and independent component analysis (ICA) were evaluated for their ability to remove residual fMRI gradient-induced signal contamination in EMG data. Contractions of ankle tibialis anterior and index finger abductor were clearly distinguishable, although observing contractions from the wrist flexors proved more challenging. To demonstrate the potential utility of simultaneous EMG and fMRI, data from the ankle experiments were analyzed using two approaches: 1) assuming contractions coincided precisely with visual cues, and 2) using EMG to time the onset and offset of muscle contraction precisely for each participant. Both methods produced complementary activation maps, although the EMG-guided approach recovered more active brain voxels and revealed activity better in the basal ganglia and cerebellum. Furthermore, numerical simulations confirmed that precise knowledge of behavioral responses, such as those provided by EMG, are much more important for event-related experimental designs compared to block designs. This simultaneous EMG and fMRI methodology has important applications where the amplitude or timing of motor output is impaired, such as after stroke.

Temporal modulations of agonist and antagonist muscle activities accompanying improved performance of ballistic movements

Although many studies have examined performance improvements of ballistic movement through practice, it is still unclear how performance advances while maintaining maximum velocity, and how the accompanying triphasic electromyographic (EMG) activity is modified. The present study focused on the changes in triphasic EMG activity, i.e., the first agonist burst (AG1), the second agonist burst (AG2), and the antagonist burst (ANT), that accompanied decreases in movement time and error. Twelve healthy volunteers performed 100 ballistic wrist flexion movements in ten 10-trial sessions under the instruction to "maintain maximum velocity throughout the experiment and to stop the limb at the target as fast and accurately as possible". Kinematic parameters (position and velocity) and triphasic EMG activities from the agonist (flexor carpi radialis) and antagonist (extensor carpi radialis) muscles were recorded. Comparison of the results obtained from the first and the last 10 trials, revealed that movement time, movement error, and variability of amplitudes reduced with practice, and that maximum velocity and time to maximum velocity remained constant. EMG activities showed that AG1 and AG2 durations were reduced, whereas ANT duration did not change. Additionally, ANT and AG2 latencies were reduced. Integrated EMG of AG1 was significantly reduced as well. Analysis of the alpha angle (an index of the rate of recruitment of the motoneurons) showed that there was no change in either AG1 or AG2. Correlation analysis of alpha angles between these two bursts further revealed that the close relationship of AG1 and AG2 was kept constant through practice. These findings led to the conclusion that performance improvement in ballistic movement is mainly due to the temporal modulations of agonist and antagonist muscle activities when maximum velocity is kept constant. Presumably, a specific strategy is consistently applied during practice.

Intramuscular injection of botulinum toxin for the treatment of wrist and finger spasticity after stroke

Botulinum toxin is effective in reducing spasticity post stroke. As there are limited data on post stroke spasticity in Asia, we undertake this study to determine the effectiveness and safety of intramuscular injection of botulinum toxin type-A (BTX-A), in the treatment of chronic focal post-stroke hand spasticity, and the impact of BTX-A on the activities of daily living and quality of life, in comparison to placebo, in Malaysian stroke patients. This was a randomized, double-blind, placebo-controlled study to assess the efficacy and safety of BTX-A in 27 subjects with wrist and finger spasticity after a stroke. The outcome measures were assessed with the Modified Ashworth Scale (MAS) to assess spasticity of the flexor muscles, Barthel Index (BI) for activities of daily living and EQ-5D and EQ VAS for quality of life. Assessments were performed at baseline and 1 and 3 months after injection. Compared to placebo, the BTX-A group had greater improvement in the flexor tone of the wrist and fingers (p = 0.001 and p < 0.001, respectively), at first month follow-up visit and sustained the improvement through to three months. Although there was an improvement in the measures of global function and quality of life in the BTX-A group, there was no significant improvement in between the two groups. No serious BTX-A related adverse effects were reported. The results of this study demonstrate that intramuscular injection of botulinum toxin A is safe and effective in the treatment of chronic focal post-stroke spasticity of the hand.

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.

Sympathetic skin responses from postauricular region in Meniere’s disease

OBJECTIVE

To investigate the sympathetic nervous system activity in Meniere's disease (MD) by recording sympathetic skin responses (SSRs) from the postauricular region (PA).

METHODS

Twenty-one patients with definite unilateral MD diagnosis and 12 healthy volunteers were studied by evoking right and left PA-SSRs with electrical stimulation of the left median nerve at the wrist in attack and interval periods of MD. Mean latencies and maximum amplitudes were used in statistical analyses.

RESULTS

In unilateral definite MD patients, the mean latencies were longer and the maximum amplitudes were smaller on the involved ear side than those on the normal ear side (p<0.01 for both amplitude and latency) and than those from the controls (p<0.01 and p<0.05). In three patients, there was no detectable PA-SSR on the involved ear side while there were SSRs on the healthy side. In four patients, the responses were absent bilaterally during the attack period.

CONCLUSIONS

There is a marked asymmetric sympathetic hypofunction in the area of the PA region of the involved ear in MD patients.

SIGNIFICANCE

The PA region is a new site for recording sympathetic skin responses. PA-SSR is a useful tool to investigate sympathetic nervous system function in MD patients.

Innervation of the triangular fibrocartilage complex of the human wrist: Quantitative immunohistochemical study

The distribution of neural elements in the triangular fibrocartilage complex (TFCC) of the human wrists was studied via immunohistochemical staining of protein gene product (PGP) 9.5 and calcitonin gene-related peptide (CGRP). Articular branches projecting to the TFCC arose from the dorsal branch of the ulnar nerve in all wrists examined. The TFCC is subdivided into the following six regions: the articular disc proper (ADP), meniscus homolog (MH), radio-ulnar ligament (RUL), loose part of ulnar collateral ligament (lUCL), dense part of ulnar collateral ligament (dUCL), and internal portion (IP). The IP consists of a mixture of dense and loose connective tissues enclosed by the ADP, MH, RUL, and UCL, and resides deep in the prestyloid recess, which is a pit in the MH. The densities of PGP 9.5-positive neural elements, including free nerve endings, single nerve fibers, nerve fascicles, and perivascular neural nets, were significantly higher in the IP than in other regions. Some of the neural elements except for the perivascular neural nets were positive for CGRP. The high density of neural elements in the IP suggests that sensory nerves projecting to the TFCC enter into the IP and from there distribute to adjacent regions such as the MH and RUL. Free nerve endings are responsible for pain transmission. The high density of free nerve endings in the IP suggests that the IP is a source of ulnar side wrist pain.

Alteration of motor nerve recovery cycle in multiple sclerosis

OBJECTIVE

To study peripheral motor nerve excitability in patients with multiple sclerosis (MS).

METHODS

Twenty MS patients with normal nerve conduction parameters and no predisposing factors for peripheral neuropathy were included. Compound muscle action potentials were recorded from the abductor digiti minimi muscle to paired-pulse stimulation of the ulnar nerve at the wrist, with various interstimuli intervals (ISIs) ranging from 1 to 7 ms. The motor nerve recovery cycle was studied using a subtraction method. We measured the durations of the absolute and relative refractory periods (ARP, RRP) and the percentages of refractoriness and supernormality at 2.6 and 7 ms ISIs. The results obtained in MS patients were compared to normative values established in 20 age-matched healthy subjects. Correlations were made between excitability parameters and MS type (relapsing-remitting or progressive), EDSS score, disease duration, and motor evoked potential (MEP) abnormalities.

RESULTS

Supernormality was extremely reduced, refractoriness was increased and both ARP and RRP were prolonged in MS patients vs. healthy controls. These alterations did not correlate to clinical features or to the presence of MEP abnormalities.

CONCLUSIONS

Changes in motor nerve recovery cycle revealed the existence of subtle impairment in the peripheral nervous system of MS patients, mainly characterized by a reduced supernormality.

SIGNIFICANCE

Peripheral nerve excitability alterations in MS may be due to axoglial paranodal dysjunction or juxtaparanodal dysfunction.

The tabatière anatomique

There is scant detailed information regarding the tabatière anatomique (anatomical snuff box) in the literature. The authors dissected this area in 15 adult cadavers (30 sides) and made measurements and observations of this region. We found that the average mean width and length of this geometric area was 4 cm and 6 cm, respectively. Although the dimensions of the tabatière anatomique tended to be larger among male specimens this trend did not reach statistical significance (P > 0.05). There was no statistical difference between left and right sides. The majority (70%) of specimens was noted to have connections between the cephalic vein and the vena comitantes of the radial artery within the tabatière anatomique. Five specimens were noted to have a muscular branch to the abductor pollicis brevis muscle arising from the dorsalis pollicis artery in the tabatière anatomique. The dorsalis pollicis artery was found to originate in the tabatière anatomique in all specimens. One right-sided specimen was noted to have an intraosseous branch of the radial artery that entered the styloid process of the radius. A well-formed collection of fat was noted between the styloid process and base of the first metacarpal in all specimens. This fat pad completely covered the radial artery in the majority of specimens and had loose connections to both the first and second dorsal compartments. The branches of the superficial branch of the radial nerve always originated distal to the tendon of the EPB muscle. These data may prove useful to the surgeon or clinician who operates or examines this interesting anatomical area.

Acrel’s ganglion

No data exists in the extant literature regarding the distal swelling of the posterior interosseous nerve (Acrel's ganglion). To further elucidate this ganglion, ten adult cadavers (20 sides) underwent dissection and histological examination of this structure. No inflammatory response was noted in these histologically normal peripheral nerve structures. No neuronal cell bodies were identified. Although the etiology of such swellings is unclear, the term "ganglia" should not be applied to these enlargements of the distal posterior interosseous nerve.

Pronation Test: Eyes Closed or Open?

BACKGROUND

The pronation test reveals slight paresis in the upper limbs. Patients hold their arms outstretched in front of them with the hands supinated while they keep their eyes closed. Position changes such as pronation, abduction, or drift indicate a positive pronation test. However, proprioceptive disorders also result in position changes when the eyes are closed.

AIM

To evaluate the effects of vision on the pronation test and the relation of test results to electrophysiological findings.

METHODS

Sixteen patients with slight unilateral paresis due to recent stroke were included in the study. Two pronation tests, one while the patients' eyes were open and the other while the eyes were closed (in randomized order), were performed in all patients and recorded with a video camera. Two neurologists double-blinded to the position of the patients' eyes then assessed the position changes in each recording. Electrophysiological examination included median sensory and motor evoked potentials in both upper limbs. Sensory and motor central conduction times (CCTs) were determined for all patients.

RESULTS

Assessments of position changes by two physicians were concordant. Ten patients had position changes more evident in the pronation test with the eyes closed (group 1), while 6 patients had similar position changes in both tests (group 2). Motor CCT difference between two sides was similar in the two groups. However, sensory CCT difference longer than 1.0 ms was significantly more frequent in group 1 (p < 0.01).

CONCLUSION

All patients who developed more obvious position changes during the pronation test with eyes closed had sensory CCT abnormalities. Therefore, we suggest that patients should keep their eyes open and then close them during the pronation test in order to distinguish motor or proprioceptive involvement.

Functional evaluation of cerebral cortex in dementia with Lewy bodies

Neurochemical investigations have demonstrated central cholinergic dysfunction in patients with dementia with Lewy bodies (DLB). Central cholinergic circuits of the human brain can be tested non-invasively by coupling peripheral nerve stimulation with transcranial magnetic stimulation of the contralateral motor cortex. This test, named short latency afferent inhibition has been shown in healthy subjects to be sensitive to the blockage of muscarinic acetylcholine receptors and it is impaired in patients with Alzheimer disease (AD), a cholinergic form of dementia, while it is normal in non-cholinergic forms of dementia such as fronto-temporal dementia. We evaluated short latency afferent inhibition in a group of patients with DLB and compared the data with that from a group of AD patients and a control group of age-matched healthy individuals. Short latency afferent inhibition was significantly reduced in DLB and AD patients. The findings suggest that this method can be used as a non-invasive test for the assessment of cholinergic pathways in patients with dementia and may represent a useful additional tool for discriminating between cholinergic and non-cholinergic forms of dementia.

Parallels in control of voluntary and perturbation-evoked reach-to-grasp movements: EMG and kinematics

To determine the potential differences in control underlying compensatory and voluntary reach-to-grasp movements the current study compared the kinematic and electromyographic profiles associated with upper limb movement. Postural perturbations were delivered to evoke compensatory reach-to-grasp in ten healthy young adult volunteers while seated on a chair that tilted as an inverted pendulum in the frontal plane. Participants reached to grasp a laterally positioned stable handhold and pulled (or pushed) to return the chair to vertical. The distinguishing characteristic between the two behaviors was the onset latency and speed of movement. Consistent with compensatory balance reactions, the perturbation-evoked reach response was initiated very rapidly (137 vs. 239 ms for voluntary). As well the movement time was shorter, and peak velocity was greater for PERT movements. In spite of the profound differences in timing, the sequence of muscle activity onsets and the order of specific kinematic events were not different between maximum velocity voluntary (VOL) and perturbation-evoked (PERT) reach-to-grasp movements. Peak velocity and grasp aperture occurred prior to hand contact with the target for PERT and VOL movements, and wrist trajectory was influenced by the direction of perturbation relative to the target. To achieve such target specific control for responses initiated within 100 ms of the perturbation, and when characteristics of body movement were unpredictable, the perturbation-evoked movements would need to incorporate sensory cues associated with body movement relative to the target into the earliest aspects of the movement. This suggests reliance on an internal spatial map constructed prior to the onset of perturbation. Parallels in electromyographic and kinematic profiles between compensatory and voluntary reach-to-grasp movements, in spite of temporal differences, lead to the view they are controlled by common neural mechanisms.

Median-radial sensory nerve comparative studies in the detection of median neuropathy at the wrist in diabetic patients

OBJECTIVE

Median-ulnar comparative studies (MUCS) play an important role in the electrodiagnosis of carpal tunnel syndrome, but in diabetes concomitant involvement of Guyon's canal (ulnar nerve compression at the wrist) would reduce the sensitivity of MUCS. This study tested the utility of median-radial comparative studies (MRCS) in diabetic patients.

METHODS

Anti-dromic MUCS and MRCS were prospectively performed in 120 patients with diabetes, and 64 normal controls. In 28 diabetic patients, latent addition using threshold tracking was performed in superficial radial sensory axons to estimate persistent nodal sodium currents.

RESULTS

MUCS was abnormal in 49% of the diabetic patients, and MRCS was abnormal in 58%. Median motor distal latencies were prolonged in 38%, and median sensory nerve conduction velocities were slowed in 40%. The longer latency differences in MRCS were associated with smaller persistent sodium currents, suggesting that intra-axonal sodium accumulation mediated by hyperglycemia enhances nerve compression.

CONCLUSIONS

MRCS appears to be the most sensitive electrodiagnostic test in the detection of median neuropathy at the wrist in diabetic patients. Nerve conduction slowing across the carpal tunnel may be associated with metabolic abnormalities under hyperglycemia.

SIGNIFICANCE

Assessment of nerve conduction across the common entrapment sites could provide new insights into the pathophysiology of diabetic neuropathy related to metabolic factors.

Changes in Spinal Excitability After PAS

Repetitive pairing of a peripheral stimulation with a magnetic transcortical stimulation (PAS) is widely used to induce plastic changes in the human motor cortex noninvasively. Based on the contrast between PAS-induced increase of corticospinal excitability and absence of PAS-induced increase of the spinal F wave size, it has been generally accepted that PAS-induced plasticity is cortical in origin. Here, instead of F waves, we used H reflex recruitment curves to assess spinal excitability, and we demonstrate that PAS induces parallel changes in cortical and spinal excitability.

Neural and Electromyographic Correlates of Wrist Posture Control

In identical experiments in and out of a MR scanner, we recorded functional magnetic resonance imaging and electromyographic correlates of wrist stabilization against constant and time-varying mechanical perturbations. Positioning errors were greatest while stabilizing random torques. Wrist muscle activity lagged changes in joint angular velocity at latencies suggesting trans-cortical reflex action. Drift in stabilized hand positions gave rise to frequent, accurately directed, corrective movements, suggesting that the brain maintains separate representations of desired wrist angle for feedback control of posture and the generation of discrete corrections. Two patterns of neural activity were evident in the blood-oxygenation-level-dependent (BOLD) time series obtained during stabilization. A cerebello-thalamo-cortical network showed significant activity whenever position errors were present. Here, changes in activation correlated with moment-by-moment changes in position errors (not force), implicating this network in the feedback control of hand position. A second network, showing elevated activity during stabilization whether errors were present or not, included prefrontal cortex, rostral dorsal premotor and supplementary motor area cortices, and inferior aspects of parietal cortex. BOLD activation in some of these regions correlated with positioning errors integrated over a longer time-frame consistent with optimization of feedback performance via adjustment of the behavioral goal (feedback setpoint) and the planning and execution of internally generated motor actions. The finding that nonoverlapping networks demonstrate differential sensitivity to kinematic performance errors over different time scales supports the hypothesis that in stabilizing the hand, the brain recruits distinct neural systems for feedback control of limb position and for evaluation/adjustment of controller parameters in response to persistent errors.

Induction of cortical plastic changes in wrist muscles by paired associative stimulation in healthy subjects and post-stroke patients

It has been shown on hand muscles in normal subjects that paired associative stimulation (PAS) combining peripheral nerve stimulation and transcranial magnetic stimulation (TMS) induces lasting changes in cortical motor excitability (Stefan et al., Brain 123 (Pt3):572-584, 2000). Because the motor recovery of distal upper limb and particularly wrist extension in post-stroke patients is one of the major rehabilitation challenge, we investigate here the effect of one session of paired associative stimulation on the excitability of the corticospinal projection to extensor carpi radialis (ECR) muscle (motor evoked potential size) before and after PAS in 17 healthy subjects and in two patients 5 months after stroke. The time course, the topographical specificity, changes in rest motor threshold (RMT), short intracortical inhibition and intracortical facilitation (SICI and ICF), the respective role of cutaneous and muscular afferents and the effect of a prolonged peripheral stimulation alone were also studied in normal subjects. Using a protocol derived from that of Ridding et al. J Physiol 537:623-631 (2001), PAS was able to induce lasting changes in the excitability of corticospinal projection to wrist muscles in healthy subjects and in the two post-stroke patients studied. Electrophysiological features of these plastic changes were similar to those previously observed in hand muscles: rapid evolution, 30-60 min duration, reversibility, relative topographical specificity and associative dependence suggesting an LTP-like mechanism. A contribution of cutaneous afferents in inducing PAS effects was also demonstrated. The decrease in ECR RMT after PAS observed in patients and in healthy subjects was an unexpected result because it has not been previously reported in the hand muscles of healthy subjects. However, it has been observed in dystonic patients (Quartarone et al., Brain 126:2586-2596, 2003). This suggests that other mechanisms like changes in membrane excitability could be involved in ECR facilitation after PAS. Further studies performed on patients using daily repeated PAS protocols and showing a functional improvement in hand motor function will be necessary to confirm that this technique could be relevant in motor rehabilitation, at least for some selected patients.