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Biomedical subjects

B T Shahani

Publications and source records attributed to B T Shahani.

At least 19 recordsLinked to original sources
PubMed1995

A new approach to motor unit estimation with surface EMG triggered averaging technique.

A new method for estimating the number of motor units using a surface EMG triggered averaging technique is described. This method provides an estimation of mean motor unit potential (MUP) amplitude at different levels of contraction, which can be utilized to estimate the number of motor units in a given muscle. Motor unit count estimated in abductor pollicis brevis (APB) muscle of 11 normal healthy subjects ranged from 131 to 371 with a mean of 246 +/- 68. In our preliminary study of patients with lower motor neuron lesions, there was a significant reduction in the number of motor units. We believe our new noninvasive method of motor unit counting is a relatively simple and reproducible physiological technique.

Adult↗
PubMed1992

Motor inhibition and excitation are independent effects of magnetic cortical stimulation.

We administered magnetic cortical stimulation (MCS) during voluntary contraction of intrinsic hand muscles to 8 patients with motor neuron disease (MND), 5 patients with pure lower motor neuron syndromes (LMN), a patient with severe subacute sensory neuropathy (SSN), and 10 healthy volunteers. Patients with MND had clinical evidence of upper MND and elevated thresholds for (3 patients) or absence of (5 patients) motor evoked potentials (MEPs). MCS during sustained contraction inhibited electromyographic activity in 6 of 8 patients with MND, without preceding MEPs. MCS had no effect on the electromyogram (EMG) of the other 2 patients with MND. In normal subjects and patients with LMN, inhibition of EMG was never seen without a preceding MEP, regardless of stimulus intensity. In the patient with SSN, MCS elicited normal MEPs and inhibited the EMG in a pattern similar to normal subjects, whereas supramaximal electrical stimulation of median and ulnar nerves failed to inhibit the EMG despite normal M and F responses. Our findings indicate that the inhibitory effects of MCS on EMG are not dependent solely on changes in afferent feedback caused by the muscle twitch produced by the MEP, or on Renshaw cell inhibition. We suggest that some of the inhibitory and excitatory effects of MCS on the motor system are mediated by distinct cortical elements, which may have different susceptibilities to pathophysiological processes in MND.

Adult↗
PubMed1992

Lumbosacral nerve root stimulation comparing electrical with surface magnetic coil techniques.

Stimulation of lumbosacral nerve roots using a monopolar needle electrode was compared with magnetic stimulation using a 7-cm diameter surface coil. Compound muscle action potentials were recorded from the tibialis anterior (TA) and flexor hallucis brevis (FHB) muscles. Although the mean latency of CMAPs did not differ using the two techniques, amplitudes were considerably larger using a needle. Mean amplitudes were 66% (TA) and 64% (FHB) of the direct M response obtained by distal, supramaximal stimulation compared with mean values using maximal magnetic coil stimulation of 36% (TA) and 25% (FHB). Minimum F-wave latencies from FHB were used to estimate the site of nerve root stimulation using both techniques. Although there was a large amount of variability in the data from individual subjects, the results suggested that, on the average, both forms of stimulation act proximal to the intervertebral foramen. We conclude that a needle electrode is a more suitable technique for stimulating lumbosacral nerve roots.

Action Potentials↗
PubMed1992

Familial bilateral carpal tunnel syndrome: report of two families.

Cases of familial carpal tunnel syndrome without other associated conditions are rare. We report two families in which multiple members had bilateral carpal tunnel syndromes. The pattern was consistent with autosomal dominant inheritance. Electrophysiologic studies were performed on nine of the 15 patients, and they demonstrated bilateral pathology of the median nerves at the wrist in all but one patient, without evidence for subclinical, generalized peripheral neuropathy. Quantitative sensory testing was performed in two cases, and it corroborated the absence of peripheral neuropathy. Five of the six patients who underwent carpal tunnel release improved after surgery.

Adolescent↗
PubMed1992

Motor nerve inexcitability in Guillain-Barré syndrome. The spectrum of distal conduction block and axonal degeneration.

We studied 34 patients with the Guillain-Barré syndrome (GBS) to clarify the clinical significance of inexcitable motor nerves and of low amplitude compound muscle action potentials (CMAPs). The patients were subdivided into two groups. Group 1 included eight patients who had electrically inexcitable motor nerves within 2 wks of the first symptom. (Two patients without extensive conduction studies had only one inexcitable motor nerve.) The outcome in this group at 1 yr varied from complete recovery (five patients) to severe motor sequelae (three patients). Group 2 included 26 patients who had two electrophysiological assessments, and in whom the serial changes in CMAP amplitudes were analysed and correlated to outcome. Fourteen of these 26 sets of serial studies were performed within 1 mth. Twelve of 26 patients in Group 2 showed decrease in the amplitude of CMAPs between serial studies; only six of these had a good outcome at 1 yr. Nine of 26 patients showed increase in CMAP amplitude between serial studies, of these eight had a good clinical outcome. Low-amplitude CMAPs or inexcitable motor nerves in the initial stages of GBS are due to distal pathology of the motor axons, either distal conduction block or axonal degeneration. The nature of these changes cannot be predicted by the results of the initial electrophysiological evaluation, including the presence or absence of active denervation. However, improvement of CMAP amplitude on sequential studies suggests a good outcome at 1 yr. We believe that, in the absence of a biological marker for GBS, individualization of an 'axonal variant' of the syndrome is not warranted at the present time.

Action Potentials↗
PubMed1992

The Lambert-Eaton myasthenic syndrome: a cause of delayed recovery from general anesthesia.

A 70-year-old man required prolonged ventilation after surgery to remove a rectal neoplasm. The cause of the slow recovery from the effects of neuromuscular blocking agents used during his anesthetic was the Lambert-Eaton myasthenic syndrome (LEMS). Before surgery, he had no neuromuscular symptoms, even in retrospect. LEMS should be considered in the diagnosis of prolonged recovery from neuromuscular blockade, even in previously asymptomatic patients.

Adenocarcinoma↗
PubMed1991

Abnormal single motor unit behavior in the upper motor neuron syndrome.

We studied the discharge pattern of single motor units (SMUs) in the left and right biceps muscles from a patient with nonspastic weakness of the left arm. Detailed statistical analysis of the behavior of discharge patterns of 4 of 4 single motor units on the affected side showed abnormalities with characteristic features of an upper motor neuron lesion. Five out of 5 single motor units recorded from the right biceps were normal. An upper motor neuron lesion affecting the left arm, predicted by our results, was confirmed by magnetic resonance imaging (MRI), which showed a lesion in the right precentral gyrus. It appears that changes in single motor unit firing characteristics, caused by an upper motor neuron lesion, can be detected at a time when there is no evidence of increased "tone" and/or hyperreflexia (spasticity) in the affected extremity.

Arm↗
PubMed1991

Hemispheric threshold differences for motor evoked potentials produced by magnetic coil stimulation.

A brief monophasic pulse through an electromagnetic coil preferentially activates motor pathways of each hemisphere, depending on the direction of coil current flow. Using the preferred direction for each hemisphere, the minimum stimulus intensity (threshold) that evoked compound muscle action potentials in the contralateral abductor digiti minimi (ADM) muscle was significantly less for the left hemisphere than the right. Threshold for biceps on each side was significantly higher than ADM, but there was no side-to-side difference. Assessing handedness using a standard handedness index, those who had less tendency to use the right hand for everyday tasks had greater differences between hemispheres for ADM thresholds. The lower threshold of the left-hemisphere projection to hand muscles is probably related to the asymmetry of corticomotoneuronal monosynaptic connections; a greater number project to the motor neuron pool of the right- than left-hand muscles.

Action Potentials↗
PubMed1990

RR interval variation and the sympathetic skin response in the assessment of autonomic function in peripheral neuropathy.

The diagnostic value of two simple tests of autonomic function, the RR interval variation and the sympathetic skin response, was evaluated relative to symptoms of dysautonomia in 53 patients with peripheral neuropathy. Of 22 patients with peripheral neuropathy and clinical dysautonomia, 15 showed abnormal results on both tests, and 7 had abnormal results on one test only. In none of the patients with dysautonomia were both tests' results normal. Conversely, all 15 patients with abnormal results of both sympathetic skin response and RR interval variation had symptoms of dysautonomia, while 7 of 15 patients with abnormalities limited to one test had such symptoms. No patient with normal results on both tests had clinical dysautonomia. These data indicate that RR interval variation and sympathetic skin response, both of which can easily be performed in the electromyography laboratory, are helpful in combination in the assessment of autonomic function in peripheral neuropathies.

Adolescent↗
PubMed1990

Electrodiagnostic abnormalities in 113 consecutive patients with Guillain-Barré syndrome.

We performed electrodiagnostic tests on 113 consecutive patients with acute Guillain-Barré syndrome (103 within 3 weeks of onset). The most common motor conduction abnormalities were proximal conduction block alone (27%), proximal block associated with a distal lesion (27%), and generalized slowing (22%). Other combinations of abnormalities each occurred in fewer than 10% of patients. Thirty-seven percent of patients initially had normal sensory nerve conduction study results, most often in association with proximal conduction block. The characteristic early electrodiagnostic changes in Guillain-Barré syndrome were often present when cerebrospinal fluid protein concentration was still normal. Extensive early fibrillations occurred in 10 patients, 6 of whom recovered well. Patients with early generalized slowing of motor nerve conduction velocity, combined abnormalities, or low muscle action potential amplitudes in ulnar, median, and peroneal nerves generally, but not always, had poorer outcomes than patients with conduction block in one nerve segment. There was no consistent relationship between results of electrophysiologic studies and overall clinical grade or limb power, except that none of the patients with an isolated proximal block had virtual or complete paralysis in the same limb.

Adolescent↗
PubMed1990

Spatial dispersion of magnetic stimulation in peripheral nerves.

To assess the longitudinal dispersion of the stimulus induced by the magnetic coil, collision experiments were performed in seven normal ulnar nerves. A supramaximal electrical stimulus S1 was delivered at the wrist, and followed by a supramaximal stimulus S2 in the upper arm, which was either electrical (electrical collision studies), or magnetic (magnetic collision studies). The interstimulus interval was varied by 0.2 msec increments from the time of complete cancellation of the S2 evoked motor response onwards, to include the entire span of recovery of that compound motor action potential. Collision curves were obtained for both magnetic and electrical stimuli by plotting the amplitude of the motor response elicited by S2 as a function of the interstimulus interval. In all seven normal ulnar nerves, comparison of the collision curves showed that the S2 evoked motor response is restored significantly more slowly when magnetic stimulation is used. This finding is best explained by longitudinal dispersion of the stimulus induced by the magnetic coil relative to conventional electrical stimulation, the large fibers being stimulated further away from the coil than the small ones. This interpretation is confirmed by the findings obtained with the same method in two cases of ulnar neuropathy, and by comparison of different intensities of magnetic stimulation.

Action Potentials↗
PubMed1990

Cervical magnetic stimulation.

We stimulated the cervical region with a 9-cm-diameter magnetic coil on centered on the spinous processes in 21 normal subjects. We obtained maximal amplitudes with clockwise coil current in right-sided upper extremity muscles and counterclockwise coil current in left-sided upper extremity muscles. Optimal stimulation sites for biceps, triceps, and abductor digiti minimi were C-3 or C-4, C-4 or C-5, and C-4, C-5, or C-6, respectively. The latencies of the muscle responses varied little in the same subject in spite of marked amplitude changes due to suboptimal position of the coil or submaximal stimulator output. In abductor digiti minimi, the amplitude of the muscle response on cervical magnetic stimulation was 9 to 100% of the supramaximal amplitude on wrist electrical stimulation. We established normal values for latency, amplitude, and interside differences for the above 3 upper extremity muscles. The findings were reproducible, and the latencies obtained with large coils from different manufacturers in the same subjects were comparable. We found no advantage in bipolar recording over tendon-belly montage. Comparison of magnetic and electrical needle root stimulation in the same subjects showed that the magnetic stimulus was more proximal in biceps and triceps, and that the site of excitation was approximately the same in abductor digiti minimi. Indirect assessment of the longitudinal site of excitation based on F-wave minimal latency indicated that excitation occurred within millimeters of the emergence of axon of the peripheral motor neuron.

Adult↗
PubMed1990

Variability of quantitative sensory testing: implications for clinical practice.

The conventional estimation of motor, sensory, and mixed nerve conduction velocities reflects activity in the fastest conducting, heavily myelinated nerve fibers that are only a small proportion of the total. Unmyelinated and thinly myelinated fibers are not evaluated by this technique and numerically represent the largest group of fibers in human cutaneous nerves. The availability of new quantitative techniques to study this aspect of sensory function is an important addition to standard electrodiagnosis. Patient understanding and cooperation is essential because subjective responses are evaluated. We evaluated a reference range for 20 healthy subjects as well as variability on repeated testing. Vibration and thermal thresholds were measured bilaterally at several sites. Measurements were repeated at intervals ranging from two days to three months. There was no side difference but substantial site differences were noted for all measurements. Intraindividual variation was substantial but within the expected range for a psychophysiologic test. Close correlation was noted between various measurements at same and different sites, indicating a great degree of interindividual variation. The Marstock method is recommended for routine clinical use.

Adult↗
PubMed1989

Relapsing bilateral brachial plexopathy during pregnancy. Report of a case.

We describe a case of relapsing bilateral brachial plexopathy occurring during pregnancy and the postpartum period. This condition is known to occur with a familial predilection, but it has not been previously reported on a sporadic basis. The outcome was poor and associated with several psychosocial consequences.

Adult↗
PubMed1989

Electrophysiologic evaluation of spinal cord motor conduction.

Spinal cord motor conduction was determined by stimulating with a monopolar needle at the C5 cord level and recording evoked motor potentials from the ipsilateral tibialis anterior muscle. Minimal F wave and direct motor latencies from the peroneal nerve were used to calculate peripheral conduction time. Mean velocity index (defined as the distance from C5 to L4 divided by central conduction time) of 15 normal subjects was 64.9 m/sec (SD 7.5). In 5 patients with multiple sclerosis the mean velocity index was 40.6 m/sec (SD 6.5), whereas in 3 patients with cervical myelopathies, due to extradural compression, the mean velocity index was 32.8 m/sec. A repeat study in one of the latter patients, 4 days after removal of a C5 disc, documented a marked improvement in cord conduction. In a patient with a thoracic and cervical syrinx, cervical cord stimulation on the clinically affected side failed to evoke a motor potential, whereas the unaffected side was normal. This method provides a simple and effective way to evaluate spinal cord motor conduction using routine electrodiagnostic equipment.

Action Potentials↗