Biomedical subjects
L R Robinson
Publications and source records attributed to L R Robinson.
AAEM case report #24: electrodiagnosis in posttraumatic syringomyelia.
An adult male with C-7 quadriplegia developed neck pain. Axillary F central latencies were prolonged, and MRI showed a syrinx extending to C-1. After shunting, F latencies normalized. At subsequent follow-up, a rostral syrinx persisted by magnetic resonance imaging (MRI); motor evoked potential (MEP) latencies were prolonged but F latencies were normal. Later, the syrinx was less distended by MRI, MEPs normalized, and strength improved. We discuss the electrophysiologic methods available for diagnosing and monitoring posttraumatic syringomyelia.
Height is an independent risk factor for neuropathy in diabetic men.
Height may increase the risk of diabetic polyneuropathy, but previous studies are inconclusive. Our purposes were to further examine the hypothesis that height (HT) is an independent risk factor for diabetic polyneuropathy and to determine which electrophysiologic measures are influenced by HT in diabetic subjects. We studied 170 Japanese American men (ages 43-73 years, mean 61) including: 69 diabetic men (mean HT 166 cm), 54 normal men (mean HT 167 cm), and 47 men with impaired glucose tolerance (IGT) (mean HT 164 cm), measuring 28 nerve conduction study (NCS) parameters. We used data from normal men in developing regression models to adjust NCS parameters for HT, age, and temperature. Factor analysis was employed to reduce the 28 NCS parameters to five physiologically meaningful factors, one of which, a factor representing median and peroneal sensory amplitudes, was significantly correlated with HT (r = -0.38, P = 0.0011) in diabetic men; taller subjects having smaller sensory nerve amplitudes. No significant correlation was found between this factor and body mass index. This factor had no correlation with HT in normal or IGT men. Our data do not confirm previous reports of associations between HT and slowed motor conduction velocities in diabetic subjects. This study does, however, support the hypothesis that HT is an independent risk factor for sensory polyneuropathy in diabetic subjects.
Electrophysiologic findings in post-traumatic syringomyelia: implications for clinical management.
Traumatic spinal cord injured (SCI) patients may develop pain, new weakness and/or sensory loss due to an enlarging fluid-filled cyst in the spinal cord. The clinical history and physical exam are nonspecific and insensitive, particularly for diagnosing and monitoring recurrent or progressive post-traumatic syringomyelia (PTS). We compare the sensitivity and specificity of three electrodiagnostic tests, median and ulnar F waves, electromagnetic motor evoked potentials (MEP), and needle electromyography, with respect to syrinx by imaging (MRI or CT scan) and neurologic progression on serial clinical exams. Central motor conduction time (CMCT) calculated from scalp and spine MEP was the most sensitive diagnostic test. F waves were less sensitive and less specific than the CMCT, and did not provide evidence of syrinxes in the mid or upper cervical cord. Positive sharp wave and fibrillation potentials were the least sensitive and least specific. The CMCT is a useful adjunct to imaging studies for diagnosing and monitoring PTS.
Interelectrode distance: a method for fixing electrode separation. A commentary.
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Contralateral v ipsilateral cane use. Effects on muscles crossing the knee joint.
Although using a cane contralaterally has been shown to reduce muscular activity across the hip joint, little is known about effects on the knee. We measured muscular activity around the knee in 10 able-bodied subjects. We simultaneously recorded integrated rectified surface electromyographic activity from the right quadriceps, medial and lateral hamstrings, gastrocnemius and hip abductors during various standing maneuvers: two-legged stance, unsupported one-legged stance and one-legged stance putting maximal, moderate (20% body weight) or minimal (10% body weight) force through an ipsilateral or contralateral cane. Electromyographic activity was expressed as the percentage of that recorded during unsupported one-legged stance in each muscle. Hip abductor activity was lowest when maximal weight was placed through a contralateral cane (66%) and highest with maximal weight ipsilaterally (424%). Medial hamstrings activity increased by 404% and 200%, respectively, when maximal and moderate force was applied to a contralateral cane, although there was no change with ipsilateral cane. Lateral hamstrings were also most active during contralateral cane use. Quadriceps activity decreased using a cane in either hand with moderate or minimal force (range 57 to 84%). Gastrocnemius activity decreased during contralateral (60 to 66%) and ipsilateral (75 to 96%) cane use. This data suggests that forces generated by muscular activity around the knee are not uniformly diminished by holding a cane in the contralateral hand and may even be increased.
Factor analysis. A methodology for data reduction in nerve conduction studies.
Analyzing multiple nerve conduction study parameters individually is statistically problematic. The goal of this study was to develop a useful factor analysis scheme for assessment of nerve conduction study abnormalities in diabetic neuropathy. Hypotheses were: (1) factor analysis produces a few physiologically meaningful factors, (2) there are associations between factors and markers of diabetic severity and (3) clinical impressions are related to factor scores. We studied 165 Japanese-American men: 52 nondiabetic, 66 diabetic and 47 with impaired glucose tolerance. One author (W.C.S.) obtained 28 nerve conduction study parameters in all subjects and factor analysis extracted five factors from these parameters. These factors were related to conduction velocities (factor 1), distal ulnar function (factor 2), sensory amplitudes (factor 3), distal median function (factor 4) and distal peroneal function (factor 5); together, they explain 57% of the variability in the total data. Diabetic factor scores were significantly (P less than 0.05) below that of the controls and correlations with fasting blood sugar were significant at the P less than or equal to 0.001 level. Use of this technique promises to permit sensible analysis of large amounts of data in clinical studies of diabetic and other types of polyneuropathy.
Distribution of glutamine and asparagine residues and their near neighbors in peptides and proteins.
In a statistical study of neighboring residues in 1465 peptides and proteins comprising 450,431 residues, it was found that the preferences for residues neighboring to glutamine and asparagine residues are consistent with the hypothesis that the rates of deamidation of these residues are of biological significance. Some dipeptide and tripeptide structures have special usefulness and some are especially undesirable. More such structures exist for amide residues than for other residues, and their specific types are those most relevant to the deamidation of amide residues under biological conditions.
Quantitative measurement of human physiological age by profiling of body fluids and pattern recognition.
Quantitative correlations with human age are demonstrated for 60 substances from a group of 200 substances measured in the urine of 235 men. Simplified pattern recognition calculations are used to combine these correlations into patterns of human age and to demonstrate their utility for the quantitative measurement of human physiological age and aging rate. The empirical use of these techniques for the extension of human life-span and diminution of human suffering from degenerative diseases is discussed. Current experimental limitations of this method are demonstrated and evaluated. The application of these techniques can form the basis for a significant advance in the quality of human life.
AAEM case report #22: polymyositis.
Polymyositis usually presents with progressive proximal muscle weakness, increased serum levels of muscle enzymes, inflammatory changes on muscle biopsy, and characteristic electromyographic (EMG) abnormalities. Motor unit action potential (MUAP) changes of configuration, duration, and amplitude are the most frequently observed EMG abnormality. Fibrillation potentials are commonly seen and tend to reflect active disease, diminishing after successful medical management or disease regression. Other muscle diseases can present with similar electromyographic abnormalities, thereby necessitating muscle biopsy for definitive diagnosis.
Effect of statistical methodology on normal limits in nerve conduction studies.
Mean +/- 2 standard deviations (SD), which relies on a Gaussian distribution, has traditionally been used to derive normal limits for nerve conduction studies. Our purpose was to examine skew in nerve conduction study (NCS) parameters, and to compare normal limits derived by several alternative methods. We examined 22 NCS parameters from 75 asymptomatic, nondiabetic men (controls). The coefficient of skewness (g1) was significantly positive (P less than 0.10, two-tailed test) in 5 of 8 amplitude and 6 of 8 latency measurements. Transformation reduced g1 in 19 of 22 parameters, and was optimal when g1 was closest to zero. For each measurement, ideal normal limits were defined as mean +/- 2 SD of the optimally transformed data of the control subjects. The percentage of 66 diabetic subjects classified as abnormal by the raw data, but normal by the ideal normal limits, was the positive misclassification rate; while the percentage considered normal by the raw data, but abnormal by the ideal normal limits, was the negative misclassification rate. Mean +/- 2 SD of the raw data produced up to 11% positive misclassifications and 12% negative misclassifications. When the range of observed values was used, up to 6% positive misclassifications and 13% negative misclassifications were found, while the 2.5 or 97.5 percentile values produced up to 10% positive misclassifications and 13% negative misclassifications. We conclude that analyses using the raw data to derive normal limits result in an unacceptable rate of misclassification. Normal limits should be derived from the mean +/- 2 SD of the optimally transformed data.
Limits of normal nerve function during high-frequency stimulation.
We studied the effects of prolonged high-frequency stimulation in normal rat tail nerves. Nerves could conduct impulses at 50 Hz for 5 hours without complete conduction block. However, over time there was a significant decrease in amplitude and increase in latency of the compound nerve action potential (CNAP), which gradually became desynchronized. Changes were influenced by the frequency of stimulation. When stimulating over 30 minutes at 20, 50, 100, and 143 Hz the amplitude decreased to 89%, 79%, 67%, and 65% of baseline values, respectively, whereas the latency was only significantly increased at 100 and 143 Hz. All changes were reversible upon cessation of stimulation. Changes could not be attributed to focal block at the site of stimulation. These changes in the CNAP may reflect functional limitations of the axon membrane which may have pathophysiological implications for the study of neuropathies and focal nerve lesions.
Motor-evoked potentials reflect spinal cord function in post-traumatic syringomyelia.
The purpose of this study was to examine electrophysiologic abnormalities, including motor-evoked potentials, in a patient with post-traumatic syringomyelia before and after syringopleural shunting. A patient with C5 quadriplegia presented with pain, ascending sensory loss, and new weakness in the left upper extremity two yr after spinal cord injury. MRI revealed a syrinx extending from C2 to T12. We measured central motor conduction times (CMCTs) to the biceps, median F-wave latencies, needle electromyography and motor nerve conduction studies. Six days before surgery, CMCTs were 9.0 ms on the left and 7.8 ms on the right (normal less than 8.0), median F-waves were absent on the left and needle EMG revealed evidence of denervation in the left biceps. Fifteen days after syringopleural shunting at the T7 level, CMCTs had dropped to 6.9 ms on the left and 4.6 ms on the right; the left median F-wave reappeared with a normal latency. Repeat MRI revealed the syrinx to be smaller in diameter. These results suggest that CMCTs measured from magnetic stimulation of the motor cortex may be useful in the diagnosis of post-traumatic syringomyelia, as well as for following such patients postoperatively.
Carbaryl poisoning and edrophonium: electrophysiologic changes.
A case of poisoning with the insecticide carbaryl, a cholinesterase inhibitor, was studied using repetitive stimulation and edrophonium administration. Without edrophonium, repetitive stimulation studies were normal. After 5mg of edrophonium was administered intravenously, a 40% decrement was recorded using 3Hz stimulation and an 80% decrement was seen with 30Hz stimulation. It is concluded that edrophonium is useful in testing for poisoning with cholinesterase inhibitors when other electrophysiologic studies are normal. These changes are most likely due to a recently described fast desensitization of the acetylcholine (ACh) receptor induced by high ACh concentrations.
A technique for quantifying and determining the site of isometric muscle fatigue in the clinical setting.
We investigated a clinically applicable technique for quantifying and determining the site of fatigue during isometric contraction. We measured torque in the right knee extensors of 17 able-bodied subjects during an isometric contraction for 60sec at 100%, 75%, 50%, and 25% of maximal effort. During contractions, a 0.5-sec train of 50-Hz stimulation was applied at 15, 30, and 45sec. We measured the percent decline in force over 60 sec (fatigue index) and average augmentation in torque during stimulation (AVAUGTORQ). The mean fatigue index at full effort was 25.1%. The mean AVAUGTORQ at 100%, 75%, 50%, and 25% of maximal effort was 12.1%, 26.3%, 40.5%, and 69.7% of values at complete relaxation, respectively. These methods should be clinically useful for quantifying the level of isometric fatigue, determining the site of fatigue, and measuring the level of effort in subjects without neuromuscular disease. The results agree with previous studies reporting a peripheral site of fatigue in healthy, well-motivated subjects.
Functional outcome after liver transplantation: a preliminary report.
Although the number of patients undergoing successful liver transplants each year has increased dramatically, little information is available on the functional outcome of such patients. A survey was conducted to determine the functional and vocational outcome of patients three years after orthotopic liver transplantation. Questionnaires were sent to 45 patients who had liver transplants in 1985, of whom 31 responded. Fourteen patients (47%) reported abnormal function in at least one limb; four patients (13%) reported developing gout. All patients were independent in ADLs and mobility; assistive devices were used by four patients. Nineteen patients (61%) reported severe impairment in endurance before transplant; 15 (48%) were unable to ambulate outside the house. After transplant only two patients (6%) reported severely impaired endurance, and all but two were able to walk at least three blocks. Three years after transplant, 12 patients (39%) were working full time and eight patients (26%) were homemakers. Work performance was most commonly limited by fractures (12 patients) and lack of concentration (seven patients). Thus, despite frequent limitations in limb function, patients after liver transplant are largely independent in ADLs and mobility, have improved endurance, and can often return to work despite physical limitations.
Postpartum femoral neuropathy: relic of an earlier era?
Femoral neuropathy after childbirth is rarely encountered today, although around 1900 an incidence of up to 4.7% was found. A case of postpartum unilateral femoral neuropathy in a 29-year-old primigravida is described. The patient's labor was complicated by poor progression, a prolonged second stage (three hours), and midforceps delivery. The patient received both epidural anesthesia (requiring catheter manipulation) and spinal anesthesia. Total time in the dorsal lithotomy position was four hours; total duration of labor was 27 hours. After delivery, the patient experienced buckling at the right knee and numbness down the leg anteriorly. The electromyogram at one month was consistent with an acute femoral neuropathy. Information about other cases of postpartum lower extremity neuropathy was obtained by a retrospective review of all deliveries at a large maternity hospital between 1971 and 1987. Of 143,019 live births, there were three other cases of postpartum knee extensor weakness (2.8/100,000), five cases of postpartum footdrop (3.5/100,000), and two cases of meralgia paresthetica (1.4/100,000). Although the precise mechanism of injury remains unclear, the declining incidence of femoral neuropathy may reflect decreased duration of labor with modern obstetric practices, particularly more frequent Cesarean delivery.