Retrograde changes in motor and sensory conduction velocity after nerve injury

Summary Nerve section is followed by a reduction of motor and sensory conduction velocity in the proximal segment of the injured nerve. This reduction of velocity is associated with retrograde changes in fiber size. If reinnervation does not occur within the next 1 1/2–2 years, retrograde degeneration of nerve fibers results, and the amplitude of the evoked nerve potential in the proximal segment of the injured nerve decreases. This retrograde degeneration is probably significant in view of the poor results frequently obtained after nerve transplantation which is carried out too late.

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Zusammenfassung Traumatische Nervenläsionen sind regelmäßig von einer Herabsetzung der maximalen motorischen und sensiblen Nervenleitgeschwindigkeit im supraläsionellen Abschnitt gefolgt. Dieser korrespondieren retrograde Faserveränderungen mit Reduktion des Axondurchmessers, wobei wahrscheinlich die dicken, rasch leitenden Fasern bevorzugt betroffen sind. Das Ausbleiben einer Reinnervation innerhalb von 1 1/2–2 Jahren führt vermutlich zur retrograden Faser-Degeneration, da nach dieser Zeit eine starke Erniedrigung des evozierten Nervenpotentials im proximalen Nervenabschnitt resultiert. Diese retrograde Degeneration dürfte für die oft schlechten Ergebnisse nach spät erfolgender Nerventransplantation von Bedeutung sein.

     

Distal slowing of motor nerve conduction velocity in diabetic polyneuropathy.

Using the latencies of M response and F wave, motor nerve conduction was assessed along the entire course of the nerve from the spinal cord to the muscle in 102 diabetics and 74 control patients. In diabetics, latencies were increased and conduction velocity decreased over both proximal and distal segments. However, the latency ratio of the proximal to distal segment (F ratio) was slightly but significantly smaller in diabetics (mean +/- SD:0.93 +/- 0.14, 1.35 +/- 0.20, 1.09 +/- 0.19 and 1.02 +/- 0.19 for median, ulnar, tibial and peroneal nerves, respectively) than in control patients (1.05 +/- 0.09, 1.41 +/- 0.12, 1.17 +/- 0.13 and 1.08 +/- 0.12). These findings suggest that motor conduction abnormalities in diabetic polyneuropathy are diffuse over the total length of the nerve, but more intense in the distal than proximal segment. An additional finding in diabetics was that both proximal and distal segments were more frequently affected in the lower than in the upper extremities.     

Prevalence of subclinical neuropathy in diabetic patients: assessment by study of conduction velocity distribution within motor and sensory nerve fibres

Nerve conduction velocity distribution (CVD) study is a newly-developed electrodiagnostic method for detecting alterations in the composition of nerve fibres according to their conduction velocity. The presence of subclinical neuropathy was evaluated in 138 diabetic patients by CVD study of four motor nerves (external popliteal and ulnar nerves bilaterally) and two sensory nerves (median nerve bilaterally), and the data obtained were compared with standard electrophysiological parameters in the same nerve segments. CVD studies revealed an altered distribution pattern in 106 of 129 evaluable patients for motor nerves (82%) and in 67 of 115 evaluable patients for sensory nerves (58%), while standard examination gave abnormal findings in 92 of 137 patients (67%) and in 33 of 118 patients (11%), respectively. Of the patients adequately evaluated by both techniques, 21 of 129 patients (16%) revealed altered CVD data unaccompanied by slowing of maximum nerve conduction velocity, and 37 patients of 101 (37%) showed similar findings for sensory nerves. Subclinical alterations of motor and sensory nerve CVD were not significantly related to age or to metabolic control expressed as glycated haemoglobin levels; a significantly longer duration of disease was found in patients with motor and mixed subclinical neuropathy with respect to non-neuropathic patients. The CVD study allowed us to detect subclinical abnormalities of motor and sensory nerve fibres; often this is a more sensitive method than the standard electrodiagnostic study. This method can be very useful as a diagnostic tool and in research in the study of the progression of diabetic neuropathy. Received: 21 March 1997 Received in revised form: 8 September 1997 Accepted: 7 October 1997     

Proximal sensory conduction in diabetic patients

A study of segmental conduction along the peripheral afferent pathway of the upper limbs was carried out in 44 diabetic patients and 44 controls. An abnormal proximal conduction (Erb-cervical) was observed in 9 patients (20.4%). A similar incidence of abnormalities appeared at the most distal segment (digit III-wrist). A significant relationship between the alterations of proximal conduction and the presence of clinical signs of diabetic polyneuropathy was found. A common pathogenic mechanism underlying both these disorders is suggested.     

Motor and sensory conduction velocity in Charcot-Marie-Tooth disease

Zusammenfassung Leitgeschwindigkeit in den peripheren Nerven (sensiblen, motorischen und gemischten Fasern) wurde bei 23 Patienten von Charcot-Marie-Tooth-Krankheit durchgeführt. Es wurde in den meisten Fällen eine starke Verminderung der Leitgeschwindigkeit, in allen 3 Gruppen von Fasern, insbesondere in den distalen Segmenten (Finger und Zehen) der sensiblen Fasern beobachtet. Trotzdem waren die Mittelwerte der sensiblen, motorischen und gemischten Fasern nicht sehr verschieden. Diese Befunde weisen auf eine segmentale Demyelinisierung hin, in den meisten Fällen.     

Simultaneous measurement of conduction velocity in the neural sensory and motor fibers during segmental stimulation

The study concerned the method of investigation of upper extremity nerves which makes possible a simultaneous measurement of the conduction velocity in the motor and sensory fibres over the whole length of the nerve. Recording of responses was based on the use of surface electrodes which are safe, less painful for the patient, and provide sufficiently great responses without the necessity of using the averaging technique. Owing to simultaneous responses from the motor and sensory fibre from several stimulation sites along the nerve the localization of injury and its type are easier to establish. The method is less time-consuming than the conventional one and may be used by technicians.     

Serial in vivo determination of motor conduction velocity in tails of allaxanized non-diabetic and diabetic rats

The in vivo motor nerve conduction velocity was serially measured in alloxanized non-diabetic and diabetic rat tails.Conduction velocity in the alloxanized diabetic group reduced significantly in comparison to the value before the administration of alloxan and to that of the non-diabetic group.In the temporary diabetic group conduction velocity was decreased during the diabetic period, but returned to normal values in the non-diabetic period.Our results suggest that the decreased conduction velocity in alloxanized rats is not due to such a direct neurotoxic action of alloxan on the nerve conduction velocity, but rather the secondary results of a diabetic stage.The determination of conduction velocity in the rat tail nerve in vivo is a useful tool for the neurophysiological study of experimental neuropathy since it enables one to measure serially the conduction velocity in the same rat over many days without marked injury to the nerves.     

Noninvasive measurement of central sensory and motor conduction

Potentials evoked by median and peroneal nerve stimulation were digitally filtered between 300 and 2,500 Hz to measure early latency components and assess sensory cord conduction velocity. Short (R1) and long (R2) latency reflex responses were recorded from contracting thenar and tibialis anterior muscles. R1 is considered a spinal reflex akin to the H-reflex. Clinical evidence suggests that R2 involves a reflex arc with turnaround at the motor cortex. Sensory-motor cord velocity was derived from the latencies of R1 and R2. The method can be used to compare peripheral and central sensory conduction or conduction in central sensory and motor pathways.     

Axotomy decreases conduction velocity of unmyelinated sensory fibres

We have examined the effect of axotomy on the conduction velocity of unmyelinated sensory fibres in the vagus nerve of the rabbit. In an in vitro preparation of the nodose ganglion, conduction velocity was calculated for each cell from the latency of the intracellularly recorded action potential evoked by vagus nerve stimulation. The average velocity of sensory fibres conducting at less than 1.1 m/s, was 0.53 m/s in 287 control cells and 0.45 m/s in 269 neurones recorded 10 days after cutting the vagus nerve. Therefore, peripheral axotomy decreases conduction velocity in mammalian unmyelinated sensory axons.     

Sympathetic skin response versus maximum motor and sensory conduction velocity to detect subclinical neuropathy in non-insulin-dependent diabetics.

Conventional motor (MCV) and sensory conduction velocity (SCV) of the ulnar (UN), peroneal (PN) and median nerves (MN) and the areas of sympathetic sudomotor response (SSR) recorded from the middle finger were measured on both sides in 20 normal and 20 non-insulin-dependent diabetic (NIDD) subjects. Conventional statistical tests (t test, linear correlation coefficient r) and discrimination analysis were applied to the above electrophysiological parameters. To evaluate the capability of the tests to separate NIDD diseased from normal nerves, the results were represented as generalized distances, i.e., difference between mean discriminant normalized combinations adjusted for intra-group variability. The r values were 0.92 (P less than 0.01) for the UN, 0.40 (P greater than 0.05) for the PN, and 0.86 (P less than 0.01) for the MN sensory action potential (SAP) amplitudes. No significant differences were found for normalized latencies. The r values of the SSR areas were 0.62 (P less than 0.01) at the right and 0.77 (P less than 0.01) at the left, homolaterally to the side of stimulation. SR and MCV generalized distances were 1.35 and 1.39, respectively. The discriminating power of SSR, MCV and SCV considered together was higher (2.40) than that of MCV and SCV (1.70). Since motor, sensory and autonomic alterations often did not coexist in NIDD, it was possible to find at least one type of involvement in most of the diabetic subjects.     

Cardiorespiratory reflexes, vibratory and thermal thresholds, sensory and motor conduction in diabetic patients with end-stage nephropathy

Cerebellar atrophy (CA) is a frequent finding in patients with chronic epilepsy. To find out whether the existence of CA has an influence on the tolerance of high-dose monotherapy with carbamazepine, we compared the lowest individual toxic serum levels in patients with complex focal seizures, with CA (n = 27) and without CA (n = 20) in computerized tomography (CT). There was no statistical difference between the groups, even after separating patients with mild CA (n = 20) from those with more severe damage (n = 7). In addition, other clinical, EEG and CT data also seemed to have no influence on the individual toxic threshold serum levels of carbamazepine.     

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. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:498–503, 1998.