Lower extremity sensory nerve conduction studies

The need for routine recording of sensory potentials in the lower extremity was developed in efforts to better investigate peripheral neuropathy. Sensory nerve conduction studies (NCS) are more sensitive to many abnormalities in the peripheral nervous system than the motor NCS responses. This article provides a thorough review of sensory nerve conduction studies of the lower extremity, with special emphasis on electrodiagnostic issues.     

Symmetry of normal motor and sensory nerve conduction measurements

Nerve conduction measurements in normal subjects are assumed to be symmetric, but the normal limits of symmetry have not been determined. Full data on the limits of symmetry for commonly studied nerves are important in the clinical interpretation of nerve conduction data. We selected normal electrodiagnostic studies from archived electromyographic laboratory reports that included bilateral measurements of motor and sensory nerves. Symmetry of nerve conduction measures was confirmed, and only the median and ulnar sensory nerves had significant deviations from symmetry, supporting subclinical nerve damage in the most common dominant hand. The limits of symmetry were determined by calculating the 95th percentile for the differences between sides. For motor and sensory nerves, the range of 95th percentile limits was narrower for measures in upper extremity nerves compared to lower extremity nerves. Several reasons are offered for the wider limits of symmetry in lower extremity nerves.     

Peripheral nerve repair in the hand with and without motor sensory differentiation

To investigate the value of motor sensory differentiated nerve repair, we examined a group of 9 patients with motor sensory differentiated nerve repair and a group of 13 patients without motor sensory differentiated nerve repair. The clinical and electroneurographic findings were compared. For the clinical examination, Millesi's scoring system was used. The hand function after motor sensory differentiated median nerve repair was 72% +/- 16% compared with 57% +/- 14% without motor sensory differentiation. The hand function after motor sensory differentiated median and ulnar nerve repair was 53% +/- 12% compared with 43% +/- 24% without motor sensory differentiation. After ulnar nerve repair the achieved values for hand function were high even without motor sensory differentiation. Our results indicate that intraoperative motor sensory differentiation of injured nerves is helpful to reestablish particularly the sensory function in median nerve injuries.     

Methylmercury poisoning, Clinical follow-up and sensory nerve conduction studies

Methylmercury poisoning occurred in four cases after passage of methylmercury through the food chain. The neurological damage in all four cases was severe. The damage was greater at younger ages with maximum involvement in the case of transplacental poisoning. Significant recovery occurred in two cases, but on six-year follow-up two cases remained severely impaired. Clinical and electrophysiological evidence suggests that damage to peripheral sensory nerves may not be the cause of the late sensory symptomatology.     

Polyneuropathy caused by tuberculostatics. Study of motor nerve conduction in 29 patients

This paper presents the reconstruction of an unusual case of suicide. After raiding a branch-bank a robber fled shooting with his Sauer-Western revolver caliber .44 magnum at the pursuing policemen and succeeded in wrestling a pistol Walther caliber 7,65 mm from them. Under the fire of sub-machine guns he destroyed himself by a shot to the neck. Our investigations concerned a textile damage at the front of the sweater of the deceased surrounded by primer residue, showing characteristics of a close-up shot. The damage was identified as effect of explosion gases exhausting far-off the muzzle. The distance between this injury and the bullet hole corresponded with the length of the barrel of the Sauer-Western revolver and could be used for identification; it confirmed the diagnosis of a close-up shot at the neck, too. Collateral experiments with shots from distant ranges developed spadiceous melt figures of textile fibers around the bullet hole, the appearance of which is considered proof for a close-up shot commonly.     

Motor and sensory conduction in the musculocutaneous nerve

Motor and sensory conduction velocity in the musculocutaneous nerve were determined in 51 normal subjects. The maximal velocity from the anterior cervical triangle to the axilla was the same in motor and sensory fibres. The conduction velocity decreased 2m/s per 10 years increase of age. It was 70 m/s at 15-24 years and 58 m/s at 65-74 years. The velocity of the slowest components in sensory fibres was 17 m/s. Three selected case reports illustrate the diagnostic value of the method.     

Abnormal sensory nerve conduction in multifocal demyelinating neuropathy with persistent conduction block

Two patients exhibited chronic, slightly asymmetric weakness and wasting with fasciculations of the upper limb and hand muscles. Motor nerve conduction studies showed features of multifocal conduction block in nerve segments other than those usually involved in entrapment syndromes. The F wave was markedly delayed in the median and ulnar nerves. Transcranial cortical and cervical root magnetic stimulation showed bilaterally delayed thenar responses with normal central conduction time. Needle electromyography demonstrated a chronic denervation pattern with large polyphasic motor units in several muscles of the upper limbs. Sensory symptoms were mild and limited to paresthesias in the fingertips. Sensory nerve conduction velocity and sensory nerve action potential amplitudes were normal in elbow-to-wrist and wrist-to-finger segments of the median and ulnar nerves, but there was a delayed cortical response and unrecognizable Erb's point and cervical responses in the somatosensory evoked potentials to median nerve electrical stimulation. Electrophysiologic examination was normal in most nerves of the lower limbs. These two patients, meeting clinical and electrophysiologic criteria of multifocal neuropathy with conduction block, demonstrate that sensory fibers may also be involved in this syndrome.     

Considerations in reference values for nerve conduction studies

Despite the universal application of reference values, understanding their production and underlying limitations is often overlooked. Without a deeper consideration for this issue, opportunities for treatment may be missed or misdiagnosis may occur. This article reviews relevant biostatistical issues in the generation of reference intervals and subsequent errors that may occur. Further discussion includes recommendations on how to correct statistical errors, as well as more recent methods for distinguishing between "healthy" and "diseased."     

Electrophysiologic mapping and cadaveric dissection of the lateral foot: implications for tibial motor nerve conduction studies

OBJECTIVE: To clarify, through electrophysiologic mapping and cadaveric dissection of the lateral foot, the previously published "proximal" and "distal" recording sites for tibial motor nerve conduction studies. DESIGN: Observational. SETTING: Electromyography laboratory; anatomy laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten asymptomatic feet; eight cadaveric feet. MAIN OUTCOME MEASURES: (1) Amplitudes and onset latencies of compound muscle action potentials (CMAPs) recorded over a grid on the lateral foot that included the "proximal" and "distal" recording sites; (2) nerve supply and anatomic boundaries of the abductor digiti minimi pedis (ADMP) and nearby muscles, particularly as they relate to the above recording sites. RESULTS: (1) Relatively large CMAPs were recorded at and around the "proximal" and "distal" sites, with significantly shorter "proximal" latencies. (2) In all cadaveric feet, ADMP was innervated by only the inferior calcaneal nerve (ICN) and was located deep to the "proximal" site, with virtually no muscle fibers deep to the "distal" site. The flexor digiti minimi brevis (FDMB) was conspicuously located immediately deep to the "distal" site and was innervated by only the lateral plantar nerve (LPN). CONCLUSIONS: This study strongly suggests that the "proximal" site records predominantly from the ICN-innervated ADMP, whereas the "distal" site predominantly records from the LPN-innervated FDMB.     

Myelinated sensory and alpha motor axon regeneration in peripheral nerve neuromas

Histochemical staining for carbonic anhydrase and cholinesterase (CE) activities was used to analyze sensory and motor axon regeneration, respectively, during neuroma formation in transected and tube-encapsulated peripheral nerves. Median-ulnar and sciatic nerves in the rodent model permitted testing whether a 4 cm greater distance of the motor neuron soma from axotomy site or intrinsic differences between motor and sensory neurons influenced regeneration and neuroma formation 10, 30, and 90 days later. Ventral root radiculotomy confirmed that CE-stained axons were 97% alpha motor axons. Distance significantly delayed axon regeneration. When distance was negligible, sensory axons grew out sooner than motor axons, but motor axons regenerated to a greater quantity. These results indicate regeneration differences between axon subtypes and suggest more extensive branching of motor axons within the neuroma. Thus, both distance from injury site to soma and inherent motor and sensory differences should be considered in peripheral nerve repair strategies.     

Peripheral sensory nerve dysfunction in children and adolescents with type 1 diabetes mellitus

The aim of the present study was to investigate peripheral sensory nerve function in diabetic children and adolescents without neurological symptoms. Ninety-two children and adolescents with Type 1 (insulin-dependent) diabetes mellitus (mean +/- SD age: 14.2 +/- 2.1 years, diabetes duration: 5.8 +/- 3.0 years) and 80 healthy control subjects (age: 13.8 +/- 2.2 years) matched for age, sex, body mass index, and height standard deviation score were involved in the study. Using a sine-wave transcutaneous stimulator, current perception threshold (CPT) testing at 2000, 250 and 5 Hz was performed on the left median and peroneal nerves. Diabetic children had increased CPT at 2000 Hz on both nerves as compared to the control group (median (interquartile range), median nerve: 2.43 (2.20-3.43) vs 1.80 (1.51-2.60) mA, p = 0.02; peroneal nerve: 3.51 (2.81-4.82) vs 2.70 (2.04-3.70) mA, p = 0.01). Twenty-one (23%) of patients had CPT values higher than that of any healthy individual. Of these, elevated CPT was observed in 9 (9.8%) patients on the median nerve, in 8 (8.7%) patients on the peroneal nerve, and in 4 (4.3%) patients on both median and peroneal nerves. Using multiple logistic regression analysis, worse long-term metabolic control and advanced puberty were independently predictive of peripheral sensory nerve dysfunction as the dependent variable (adjusted OR (95% CI): 3.4 (1.2-6.2), p = 0.01, and 2.8 (1.1-5.6), p = 0.03, respectively). In conclusion, evidence of peripheral sensory nerve dysfunction is not rare in children and adolescents with diabetes and can be demonstrated by CPT testing in asymptomatic patients. Poor metabolic control is a risk factor for such subclinical neuropathy, and pubertal development may be involved in the pathogenesis of diabetic peripheral neuropathy.     

A new method to determine pudendal nerve motor latency and central motor conduction time to the external anal sphincter

By placing the earth electrode between the site of the stimulus and the site of derivation, peripheral motor latency to the external anal sphincter can be determined and thus central motor conduction time (CMCT) can be calculated. In 18 volunteers we found a total motor conduction time of 19.4 msec (S.D. 1.71) after stimulation of the motor cortex and recording above the external anal sphincter. Latency was 5.6 msec (S.D. 0.66) when stimulated above L1 and pudendal latency (MEPuL) after stimulation above S3 was 2.5 msec (S.D. 0.32). CMCT to L1 (TMCT minus MCT to L1) was 13.8 msec (S.D. 1.13) and to S3 (TMCT minus MEPuL) it was 16.9 msec (S.D. 1.67). This method allows us to locate spinal dysfunction more precisely and also improves diagnosis of a possible neuropathy of the pudendal nerve.     

Correlation between evoked motor response of the sciatic nerve and sensory blockade

OBJECTIVE: The development of collateral microvessels following therapeutic angiogenesis with vascular endothelial growth factor (VEGF) was investigated using a new system of microangiography that employs monochromatic synchrotron radiation (SR) and a high definition video system to visualize arteries with a spatial resolution of 30 microns. METHODS: Ischemia was induced in the hindlimb of 20 rats by excision of the femoral artery, followed by transfection of the plasmid (400 micrograms) encoding VEGF or beta-galactosidase (control) into limb muscles. Microangiography was used to assess the development of collaterals in the ischemic limb four weeks after treatment. RESULTS: Gene transfer of VEGF produced morphologically similar, but significantly more extensive, collateral networks at the microvascular level as compared with the naturally occurring collateral arteries in the control animals (angiographic score: 0.88 +/- 0.08 versus 0.54 +/- 0.05, p < 0.01). No adverse vascular effects such as hemangiomas and/or arteriovenous (AV) fistulae were observed following VEGF treatment. The vasodilator effect of papaverine was evident in relatively large vessels in both groups. At the microvascular level (diameter < 100 microns), however, papaverine induced significant vasodilation in the VEGF-treated animals, and almost no vasodilation in the controls. CONCLUSIONS: SR microangiography allowed us to assess the development of small collateral arteries following VEGF-gene transfer. The information obtained may provide new insights regarding the collateral microcirculation and therapeutic angiogenesis.     

A central nerve conduction study in hypothyroidism: before and after thyroxine replacement

Employing a Nicolet CA 100 machine, 20 patients of primary hypothyroidism were selected for electrophysiological studies, including somato-sensory evoked potential (SSEP), brainstem auditory evoked potential (BAEP), and visual evoked potential (VEP), to assess the central nerve conduction before and after administration of the thyroid hormone. Before thyroxine replacement therapy, the latencies of N9, N13, and N20 in SSEP showed significant delay, while the central conduction time (CCT) merely had a tendency of prolongation. In BAEP, the peak and interpeak latencies delayed significantly. Additionally, the latency and amplitude of VEP also had significant difference between patients and controls. After thyroxine replacement, the SSEP, BAEP, and VEP studies revealed significant improvement, in correlation with clinical amelioration. In conclusion, the central nerve conduction would be affected in primary hypothyroidism and the improvement was usually the case, reflecting the clinical recovery after appropriate treatment. The electrophysiological study provides an objective method for monitoring the function of central nervous system in hypothyroidism before and after thyroxine treatment.     

Sex differences in sensory and motor branches of the pudendal nerve of the rat

The morphology of the pudendal nerve was quantified in adult male and female rats. The sensory branch of the pudendal nerve was about three times as large in cross section in males as in females, and the motor branch was about five times as large. Electron microscopy was used to determine the ultrastructural bases of these gross size differences. Differences that were found included greater packing density of both myelinated and unmyelinated axons in females, larger myelinated and unmyelinated axons in males, larger myelin sheaths of sensory axons in males, more numerous myelinated axons in both branches of males, and more numerous unmyelinated axons in the sensory branch of males. There was also some indication that myelinated sensory axons were more likely to branch in the dorsal clitoral nerve of females than in the homologous nerve of males. Morphological differences in the structure of pudendal axons, their associated Schwann cells, and the extracellular matrix as well as differences in sensory and motor axonal number all have potential implications for the sexual differentiation of the central nervous system and behavior.     

Peripheral nerve changes in thiamine deficiency and starvation. An electron microscopic study

The treatment of iatrogenic esophageal perforation is still today subject of discussion. The present work relates our experience on 16 cases seen between 1955 and 1976, and compares the results with the 1,310 collected by French and English literature. The etiology of perforation is: endoscopy (50.5%), dilatation (19.5%), foreign bodies (14%), surgery and other causes (16%). The mortality rate of cervical perforations is 14.5% (7.3% with medical treatment, 18% with drainage, 12.6% with suture). In the thoracic esophagus it is 32.5% (50% with medical treatment, 40% with drainage, 18% with suture). The data demonstrate that the best results are obtained with surgical treatment, that may be simple drainage when the perforation is cervical, but must be the suture in the thoracic esophagus. We must emphasize that the operation must be performed within 24 hours, because, in the cases operated on after 24 hours, the mortality rate is nearly double.     

Median and ulnar nerve conduction studies among workers: normative values

To determine normative values for nerve conduction studies among workers, we selected a subset of 326 workers from 955 subjects who participated in medical surveys in the workplace. The reference cohort was composed exclusively of active workers, in contrast to the typical convenience samples. Nerve conduction measures included bilateral median and ulnar sensory amplitude and latency (onset and peak). Workers with upper extremity symptoms, medical conditions that could adversely affect peripheral nerve function, low hand temperature, or highly repetitive jobs were excluded from the "normal" cohort. Linear regression models explained between 21% and 51% of the variance in nerve function, with covariates of age, sex, hand temperature, and anthropometric factors. The most robust models were fitted for sensory amplitudes in the median and ulnar nerves for dominant and nondominant hands. The median-ulnar difference was least sensitive to adjustment, indicating it is the best measure to use if corrections are not made to account for relevant covariates. A key point was that the magnitude of variance increased with age and anthropometric factors. These findings provide strong evidence that to improve diagnostic accuracy, electrodiagnostic testing should control for relevant covariates, particularly age, sex, hand temperature, and anthropometric factors.