Assessment of diagnostic criteria for multifocal motor neuropathy in patients included in the Italian database.

BACKGROUND AND PURPOSE: This study aimed to assess the diagnostic criteria, ancillary investigations and treatment response using real-life data in multifocal motor neuropathy (MMN) patients. METHODS: Clinical and laboratory data were collected from 110 patients enrolled in the Italian MMN database through a structured questionnaire. Twenty-six patients were excluded due to the unavailability of nerve conduction studies or the presence of clinical signs and symptoms and electrodiagnostic abnormalities inconsistent with the MMN diagnosis. Analyses were conducted on 73 patients with a confirmed MMN diagnosis and 11 patients who did not meet the diagnostic criteria. RESULTS: The European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS) diagnostic criteria were variably applied. AUTHOR: When applying the American Association of Electrodiagnostic Medicine criteria, an additional 17% of patients fulfilled the criteria for probable/definite diagnosis whilst a further 9.5% missed the diagnosis. In 17% of the patients only compound muscle action potential amplitude, but not area, was measured and subsequently recorded in the database by the treating physician. Additional investigations, including anti-GM1 immunoglobulin M antibodies, cerebrospinal fluid analysis, nerve ultrasound and magnetic resonance imaging, supported the diagnosis in 46%-83% of the patients. Anti-GM1 immunoglobulin M antibodies and nerve ultrasound demonstrated the highest sensitivity. Additional tests were frequently performed outside the EFNS/PNS guideline recommendations. CONCLUSIONS: This study provides insights into the real-world diagnostic and management strategies for MMN, highlighting the challenges in applying diagnostic criteria.

Immune-mediated polyneuropathy in cats: Clinical description, electrodiagnostic assessment, and treatment.

BACKGROUND: Suspected immune-mediated polyneuropathy has been increasingly reported in cats, especially in the last decade, but the condition remains poorly understood. OBJECTIVES: Refine the clinical description and review the classification of this condition based on electrodiagnostic investigation and evaluate the benefit of corticosteroid treatment and L-carnitine supplementation. ANIMALS: Fifty-five cats presented with signs of muscular weakness and electrodiagnostic findings consistent with polyneuropathy of unknown origin. METHODS: Retrospective, multicenter study. Data from the medical records were reviewed. The owners were contacted by phone for follow-up at the time of the study. RESULTS: The male-to-female ratio was 2.2. The median age of onset was 10 months, with 91% of affected cats being <3 years of age. Fourteen breeds were represented in the study. The electrodiagnostic findings supported purely motor axonal polyneuropathy. Histological findings from nerve biopsies were consistent with immune-mediated neuropathy in 87% of the tested cats. The overall prognosis for recovery was good to excellent, as all but 1 cat achieved clinical recovery, with 12% having mild sequelae and 28% having multiple episodes during their lifetime. The outcome was similar in cats with no treatment when compared with cats receiving corticosteroids or L-carnitine supplementation. CONCLUSIONS AND CLINICAL IMPORTANCE: Immune-mediated motor axonal polyneuropathy should be considered in young cats with muscle weakness. This condition may be similar to acute motor axonal neuropathy in Guillain-Barré syndrome patients. Based on our results, diagnostic criteria have been proposed.

Electrophysiological assessment in patients with COVID-19-related peripheral neuropathies and myopathies: a systematic review.

Neurological manifestations associated with Coronavirus Disease-2019 (COVID-19) are commonly reported, but patients were not referred to perform the electrophysiological assessment. We aimed to review the existing literature on clinical studies on COVID-19 peripheral neuropathy to correlate patients' symptoms and characteristics with nerve conduction studies/electromyography (NCS/EMG) outcomes. This protocol is registered in the Open Science Framework (https://www.doi.org/10.17605/OSF.IO/ZF4PK). The systematic search included PubMed, ScienceDirect, and Google Scholar, for articles published from December 2019 to March 2022. A total of 727 articles were collected, and according to our inclusion and exclusion criteria, only 6 articles were included. Of 195 participants, only 175 underwent NCS/EMG assessment. Of these, 44 participants (25.1%) had abnormal EMG, 54 participants (30.8%) had abnormal motor NCS, and only 7 participants (4%) had abnormal sensory NCS. All cases presented with myopathy, while a limited number of cases presented with polyneuropathy. According to motor NCS and EMG, the most affected nerves were the tibial and peroneal in the lower extremities and the ulnar nerve in the upper extremities. Interestingly, the median nerve was reported to be associated with the severity and the rate of motor recovery of patients with COVID-19. COVID-19 generates a demyelinating motor neuropathy and myopathy. Clinicians are encouraged to refer patients with COVID-19 presenting with neurological symptoms to be assessed by electrophysiological methods to objectively determine the nature of their symptoms, follow their prognosis, and plan their rehabilitation.

Assessment Of Carpal Tunnel Syndrome With Ultrasonography.

BACKGROUND: Carpal tunnel syndrome (CTS) is the most common nerve entrapment neuropathy caused by compression of median nerve at wrist as it passes through Osseo fibrous canal known as carpal tunnel. Epidemiological statistics shows one in every ten people develops the disease at any stage of life. CTS mostly affect females than males with mean age of 50. Clinical features are considered to be enough for establishing the diagnosis of carpal tunnel syndrome. However, nerve conduction studies give quantitative information regarding median nerve function therefore good at predicting outcome of intervention. Ultrasound being easily available, cost effective and real time is a promising modality for diagnosis and grading carpal tunnel syndrome. METHODS: This correlational study was conducted in collaboration of Neurology and Radiology Department of Pakistan Institute of Medical Sciences, Islamabad from January 2018 to January 2019. Total 50 patients with 85 wrists involved were included in the study. All patients with positive nerve conduction study were included. Patient with history of wrist trauma were not included. Detailed history and clinical features were recorded. All patients with positive result on nerve conduction studies underwent ultrasound examinations. Fifty control wrists were also included to establish the normal median nerve cross sectional area value in our study population. Results were recorded. Data was analyzed and appropriate statistical tests were applied by using SPSS v20. RESULTS: Mean cross sectional area of median nerve for controls was 6.34±1.23. Mean cross sectional area of median nerve for mild CTS was 8.05±1.72, moderate CTS was 11.15±2.32, severe was 17.49±4.93. Strong correlation was found between (r=0.76, p-value <0.0001) between increased cross-sectional area on Ultrasonography and severity of CTS on NCS. Other finding on Ultrasonography included flattening in 4 and fluid in 10 affected wrists. CONCLUSIONS: Increased cross-sectional area on Ultrasonography and severity of carpal tunnel syndrome on nerve conduction studies are very strongly correlated.

Changes in thumb tapping rates and central motor conduction times are associated in persons with multiple sclerosis.

INTRODUCTION: In persons with multiple sclerosis, nerve conductivity can be reduced. The assessment is generally performed via motor evoked potentials (MEP). So far, a strongly associated motor performance surrogate for changes in the extracted central motor conduction time (CMCT) is missing. METHODS: CMCT and performance in the nine-hole peg test and maximum thumb tapping frequencies over 10 s of 12 persons with multiple sclerosis were measured prior to and after training over 5 consecutive days. Each training consisted of 10,000 thumb taps at maximum effort with the dominant upper limb. RESULTS: The dominant upper limb improved in maximum tapping frequency over 10 s (d = 0.79) and 10,000 taps (d = 1.04), the nine-hole peg test (d = 0.60), and CMCT (d = 0.52). The nondominant upper limb only improved in the nine-hole peg test (d = 0.38). Models of multiple linear regression predicted 0.78 (model 1, tapping performance as factors) and 0.87 (model 2, patient baseline characteristics as factors) of the variance in CMCT changes. DISCUSSION: Changes in CMCT were well predictable, although the assessment of those surrogates is either not economic (model 1) or rather describing a potential of change (model 2). However, we were able to show moderate changes in CMCT within 5 days.

Follow-up assessment of patients with Pure Neural Leprosy in a reference center in Rio de Janeiro-Brazil.

INTRODUCTION: Pure Neural Leprosy (PNL) is a rare clinical form of leprosy in which patients do not present with the classical skin lesions but have a high burden of the disability associated with the disease. Clinical characteristics and follow up of patients in PNL are still poorly described in the literature. OBJECTIVE: This paper aims to describe the clinical, electrophysiological and histopathological characteristics of PNL patients, as well as their evolution after multidrug therapy (MDT). METHODS: Fifty-two PNL patients were selected. Clinical, nerve conduction studies (NCS), histopathological and anti-PGL-1serology were evaluated. Patients were also assessed monthly during the MDT. At the end of the MDT, all of the patients had a new neurological examination and 44 were submitted to another NCS. RESULTS: Paresthesia was the complaint most frequently reported by patients, and in the neurological examination the most common pattern observed was impairment in sensory and motor examination and a mononeuropathy multiplex. Painful nerve enlargement, a classical symptom of leprosy neuropathy, was observed in a minority of patients and in the motor NCS axonal injuries, alone or in combination with demyelinating features, were the most commonly observed. 88% of the patients did not present any leprosy reaction during MDT. There was no statistically significant difference between the neurological examinations, nor the NCS pattern, performed before and after the MDT. DISCUSSION: The classical hallmarks of leprosy neuropathy are not always present in PNL making the diagnosis even more challenging. Nerve biopsy is an important tool for PNL diagnosis as it may guide therapeutic decisions. This paper highlights unique characteristics of PNL in the spectrum of leprosy in an attempt to facilitate the diagnosis and management of these patients.

Use of Ultrasound in Patients With Carpal Tunnel Syndrome: A Cost-Effective Solution to Reduce Delays in Surgical Care.

PURPOSE: Currently, electrodiagnostic testing, which comprises electromyogram (EMG) and nerve conduction studies (NCS), is the most commonly used method for confirming the clinical diagnosis of carpal tunnel syndrome (CTS). Electromyogram and NCS can be costly, can require multiple visits, may induce anxiety, and may be painful for patients. The purpose of this study was to determine whether replacing EMG/NCS with ultrasound (US), performed by the treating surgeon, to diagnose CTS decreases time to surgery and the number of office visits. METHODS: We retrospectively reviewed a database that consisted of patients who presented to our department with numbness and/or tingling in the hand(s). We assessed the patients' histories for any subsequent carpal tunnel release, dates of diagnosis, dates of surgery, the number of CTS-related medical visits, and diagnostic methods employed. A fellowship-trained hand surgeon performed US examination, and the patients were referred for EMG/NCS testing. We collected data prior to surgery using the Boston Carpal Tunnel Questionnaire to evaluate symptom severity scale and functional status scale scores. We performed linear regression to assess differences in the time to surgery and the number of medical visits prior to carpal tunnel release. RESULTS: Patients who had the diagnosis confirmed by the surgeon using US (n = 34) underwent surgical intervention 3-4 weeks earlier, with 1.8 fewer medical visits on average than the number of medical visits for those who had their diagnosis confirmed using EMG/NCS (n = 98). CONCLUSIONS: If a confirmatory method for the diagnosis of CTS is required or desired by the treating surgeon, surgeon-conducted US might have an impact on the efficiency of care for patients with CTS. TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic IV.

iMAX: A new tool for assessment of motor axon excitability. A multicenter prospective study.

OBJECTIVE: This study was undertaken to establish by a multicentric approach the reliability of a new technique evaluating motor axon excitability. METHODS: The minimal threshold, the lowest stimulus intensity allowing a maximal response by 1 mA increments (iUP) and then by 0.1 mA adjustments (iMAX) were prospectively derived from three nerves (median, ulnar, fibular) in four university centers (Liège, Marseille, Fraiture, Nice). iMAX procedure was applied in 28 healthy volunteers (twice) and 32 patients with Charcot-Marie-Tooth (CMT1a), chronic inflammatory demyelinating polyneuropathy (CIDP), Guillain-Barré syndrome (SGB) or axonal neuropathy. RESULTS: Healthy volunteers results were not significantly different between centers. Correlation coefficients between test and retest were moderate (> 0.5). Upper limits of normal were established using the 95th percentile. Comparison of volunteers and patient groups indicated significant increases in iMAX parameters especially for the CMT1a and CIDP groups. In CMT1a, iMAX abnormalities were homogeneous at the three stimulation sites, which was not the case for CIDP. CONCLUSIONS: The iMAX procedure is reliable and allows the monitoring of motor axon excitability disorders. SIGNIFICANCE: The iMAX technique should prove useful to monitor motor axonal excitability in routine clinical practice as it is a fast, non-invasive procedure, easily applicable without specific software or devices.

Assessment of thoracic spinal cord electrophysiological activity through magnetoneurography.

OBJECTIVE: Noninvasive and detailed visualization of electrophysiological activity in the thoracic spinal cord through magnetoneurography. METHODS: In five healthy volunteers, magnetic fields around current flowing in the thoracic spinal cord after alternating unilateral and synchronized bilateral sciatic nerve stimulation were measured using a magnetoneurograph system with superconductive quantum interference device biomagnetometers. The current distribution was obtained from the magnetic data by spatial filtering and visualized by superimposing it on the X-ray image. Conduction velocity was calculated using the peak latency of the current waveforms. RESULTS: A sufficiently high magnetic signal intensity and signal-to-noise ratio were obtained in all participants after synchronized bilateral sciatic nerve stimulation. Leading and trailing components along the spinal canal and inward components flowing into the depolarization site ascended to the upper thoracic spine. Conduction velocity of the inward current in the whole thoracic spine was 42.4 m/s. CONCLUSIONS: Visualization of electrophysiological activity in the thoracic spinal cord was achieved through magnetoneurography and a new method for synchronized bilateral sciatic nerve stimulation. Magnetoneurography is expected to be a useful modality in functional assessment of thoracic myelopathy. SIGNIFICANCE: This is the first report to use magnetoneurography to noninvasively visualize electrophysiological activity in the thoracic spinal cord in detail.

Nerve conduction assessment and magnetic resonance imaging for the diagnosis of localized hypertrophic neuropathy of the sciatic nerve and the lumbo-sacral plexus.

Localized hypertrophic neuropathy (LHN) are slowly growing nerve lesions causing progressive nerve deficit and weakness. We present the case of a 32-year old woman with long history of motor and sensory deficit complains along the sciatic nerve territory. The muscles involved were featured by delay in F waves at nerve conduction assessment. Magnetic resonance imaging (MRI) showed specific patterns, low intense on T1 and abnormally hyper intense on short tau inversion recovery (STIR) and T2, with no obvious enhancement, features compatible with either LHN or intraneural perineurioma (IP) of the sciatic nerve and/or the lumbosacral plexus. Focal thickening and hypertrophy of the sciatic nerve with preserved fascicular configuration and progressive enlargement of the right lumbosacral plexus could be noted. A nerve conduction assessment followed by an MRI eventually allowed to diagnose LHN, without performing a nerve biopsy. Although similar, LHN and IP are two distinct lesions which should be diagnosed and differentiated as soon as possible, to avoid potential complications due to delayed diagnosis and/or misdiagnosis.

Assessment of sympathetic sudomotor function in amyotrophic lateral sclerosis with electrochemical skin conductance.

OBJECTIVE: Amyotrophic lateral sclerosis (ALS) is now recognized as a multisystem neurodegenerative disorder, comprising autonomic dysfunction. We aimed to assess sudomotor function in ALS by measuring the electrochemical skin conductance (ESC). METHODS: Thirty-one ALS patients [median age of 62 years (1st-3rd interquartile range - IQR, 56-72), male 71%] were prospectively compared with 29 healthy controls, matched for age and sex. We analysed ESC results from hands and feet, bilaterally. RESULTS: A total of 120 ESC recordings were obtained. Hands and feet ESC measurements were significantly lower in patients compared with controls [64 µS (1st-3rd IQR, 57-58) versus 78 µS (1st-3rd IQR, 70.5-84), p < 0.001 and 76 µS (1st-3rd IQR, 68-83) versus 81 µS (1st-3rd IQR, 78-86), p = 0.008, respectively]. In ALS group, no differences were observed between spinal and bulbar-onset forms for hands and feet results (p > 0.05). Hands and feet ESC measurements did not correlate also with disease duration, total ALSFRS-R scale, or ALSFRS-R progression rate (all p > 0.05). CONCLUSION: ESC is a non-invasive, fast and quantitative method suitable for assessing sudomotor function. ALS patients revealed a decreased function in upper and lower extremities. SIGNIFICANCE: Sudomotor dysfunction is part of the ALS manifestations.

Preliminary Risk assessment for Acrylamide and Peripheral Neuropathy.

Acrylamide (ACM) is a high-volume industrial chemical with diverse uses in manufacturing, construction and laboratory research. ACM is a well-established neurotoxic agent causing peripheral neuropathy with impairment in the arms and legs of exposed workers, most thoroughly studied in Swedish tunnel workers exposed to ACM grouting. A quantitative risk assessment was performed to assess ACM risk to workers. Using data from a published paper investigating peripheral neuropathies in Chinese chemical workers, estimates of exposure response for vibration perception threshold and nerve conduction velocities were calculated, based on hemoglobin adducts and air concentrations as exposure metrics. The benchmark dose procedure was applied in order to calculate excess risks of impairment, defined as adverse performance exceeding the 95th percentile in unexposed populations, at various concentrations of airborne ACM exposure. Under the assumptions in this risk assessment, after three years of inhalation exposure at 0.3 mg/m3, the excess attributable impairment manifest in vibration perception and nerve conduction velocity is estimated to occur in 1-2% of workers. For 10 years at 0.3 mg/m3 ACM inhalation (equivalent to 3 years at 1.0 mg/m3) the excess prevalence of impairment would be 2-14% of workers, assuming the effect continues to accrue linearly in time. Using published data, the risks of impairment from peripheral neuropathy attributable to exclusively airborne ACM exposure can be predicted for exposure periods less than 10 years. The risks associated with dermal and airborne ACM exposures can be estimated by characterizing working process environments using ACM Hb-adduct levels and possibly monitored with urinary biomarkers.

Test Utilization and Value in the Evaluation of Peripheral Neuropathies.

Peripheral neuropathies can be classified as typical or atypical. Patients with atypical neuropathy have one or more of the following features: acute/subacute onset, non-length dependence, motor predominance, or asymmetry. This classification is important because it informs the appropriate diagnostic evaluation of this highly prevalent condition. The evaluation of a typical peripheral neuropathy, also known as distal symmetric polyneuropathy, requires a thorough history, neurologic examination, and focused laboratory testing. Electrodiagnostic testing and MRI account for the majority of costs but rarely lead to changes in diagnosis or management. These costs are increasingly being passed on to patients, especially those with high-deductible health plans. In contrast, patients with atypical neuropathy require more extensive testing, including electrodiagnostic tests. These tests are much more likely to lead to the use of disease-modifying therapies in these patients compared to in those with typical peripheral neuropathy. This article describes two cases to illustrate the appropriate diagnostic workup of those with typical or atypical neuropathy.

A novel approach to the diagnostic assessment of carpal tunnel syndrome based on the frequency domain of the compound muscle action potential.

Conventional electrophysiological (EP) tests may yield ambiguous or false-negative results in some patients with signs and symptoms of carpal tunnel syndrome (CTS). Therefore, researchers tend to investigate new parameters to improve the sensitivity and specificity of EP tests. We aimed to investigate the mean and maximum power of the compound muscle action potential (CMAP) as a novel diagnostic parameter, by evaluating diagnosis and classification performance using the supervised Kohonen self-organizing map (SOM) network models. The CMAPs were analyzed using the fast Fourier transform (FFT). The mean and maximum power parameters were calculated from the power spectrum. A counter-propagation artificial neural network (CPANN), supervised Kohonen network (SKN) and XY-fused network (XYF) were compared to evaluate the classification and diagnostic performance of the parameters using the confusion matrix. The mean and maximum power of the CMAP were significantly lower in patients with CTS than in the normal group (p < 0.05), and the XYF network had the best total performance of classification with 91.4%. This study suggests that the mean and maximum power of the CMAP can be considered as less time-consuming parameters for the diagnosis of CTS without using additional EP tests which can be uncomfortable for the patient due to poor tolerance to electrical stimulation.

Assessment of Distal Motor Latency of the Femoral Nerve in Clinically Healthy Adult Dogs.

This study aimed to evaluate femoral nerve latency time recorded from both vastus lateralis and vastus medialis muscles, in clinically healthy dogs. Eighteen adult dogs were distributed into 2 distinct body mass ranges (Group 1: 1-4.1 kg, n= 9; Group 2: 4.2-13 kg, n= 8), according to the median body mass (4.1 kg). Distal motor latencies for the femoral nerve were obtained in right- and left hind limbs. Platinum surface electrodes were used to record the latency of femoral nerve from the vastus lateralis muscle, whereas coaxial needle electrodes were used to record the latency from the vastus medialis muscle. The distal motor nerve latencies were 1.52 ± .23 milliseconds and 1.69 ± .42 milliseconds, respectively, for vastus lateralis and vastus medialis muscles. There were no significant differences of distal motor nerve latencies between vastus lateralis and vastus medialis muscles. Hind limb length of Group 1 was significant shorter than Group 2. There were no significant differences of latencies between Groups 1 and 2. No significant correlations were observed between latency and body mass, and between latency and hind limb length for dogs of both groups. In conclusion, the femoral motor latency measurement was easy to obtain and may supply additional data in the examination of diseases that affect the hind limbs. Latency values of vastus lateralis longer than 1.52 ± .23 milliseconds in small/medium-sized breeds may be considered as suggestive of a femoral neuropathy.

Characteristics of patients with vitamin B12-responsive neuropathy: a case series with systematic repeated electrophysiological assessment.

BACKGROUND: Vitamin B12 (B12) has a fundamental role in both central and peripheral nervous system function at all ages. Neurologic manifestations may be the earliest and often the only manifestation of B12 deficiency. Mostly because of the poor sensitivity of methods of determination for B12 levels, peripheral neuropathy remains a classical but underdiagnosed complication of B12 deficiency. So the clinical and electrophysiological characteristics of B12-responsive neuropathy are not well known. METHODS: A retrospective study of patients with B12-responsive neuropathy was conducted at our hospital on a 3-year period. The criteria for inclusion were: (a) neuropathy confirmed by the electrophysiological study (nerve conduction study); and (b) improvement of at least 1 point of the total Overall Neuropathy Limitations Scale score after vitamin B12 treatment. RESULTS: Nine patients were identified. Serum B12 level was low in only four. Four patients had sensorimotor (predominantly sensory) axonal polyneuropathy while five had only sensory neuronopathy. Six improved in less than 1 month after B12 supplementation. CONCLUSION: B12-responsive neuropathy is a more heterogeneous group of neuropathy than previously described. B12 deficiency is a cause of peripheral neuropathy and should systematically be ruled out in the clinical setting of idiopathic neuropathy or sensory neuronopathy because of potential reversibility. ABBREVIATIONS: B12: vitamin B12; CMAP: compound muscle action potentials; DRG: dorsal root ganglia; ENMG: electroneuromyography; MCCT: motor central conduction time; MEP: motor evoked potentials; MMA: methylmalonic acid; MMCoAM: L-methylmalonyl-CoenzymeA mutase; ONLS: overall neuropathy limitations scale; SCV: sensory conduction velocities; SNAP: sensory nerve action potentials; SNN: sensory neuronopathy; SSS: SNAP sum score.

A microfabricated nerve-on-a-chip platform for rapid assessment of neural conduction in explanted peripheral nerve fibers.

Peripheral nerves are anisotropic and heterogeneous neural tissues. Their complex physiology restricts realistic in vitro models, and high resolution and selective probing of axonal activity. Here, we present a nerve-on-a-chip platform that enables rapid extracellular recording and axonal tracking of action potentials collected from tens of myelinated fibers. The platform consists of microfabricated stimulation and recording microchannel electrode arrays. First, we identify conduction velocities of action potentials traveling through the microchannel and propose a robust data-sorting algorithm using velocity selective recording. We optimize channel geometry and electrode spacing to enhance the algorithm reliability. Second, we demonstrate selective heat-induced neuro-inhibition of peripheral nerve activity upon local illumination of a conjugated polymer (P3HT) blended with a fullerene derivative (PCBM) coated on the floor of the microchannel. We demonstrate the nerve-on-a-chip platform is a versatile tool to optimize the design of implantable peripheral nerve interfaces and test selective neuromodulation techniques ex vivo.

Dynamic Quantitative Assessment of Motor Axon Sprouting after Direct Facial-Hypoglossal End-To-Side Neurorrhaphy in Rats.

BACKGROUND: End-to-side (ETS) neurorrhaphy is a promising procedure for peripheral nerve repair, yet controversies regarding the efficacy of this repair in facial nerve anastomosis for facial paralysis still exist. MATERIALS AND METHODS: Thirty rats were divided into three groups: intact control group, direct facial-hypoglossal ETS neurorrhaphy, and end-to-end (ETE) neurorrhaphy. Nerve regeneration was assessed with vibrissae motor performance, electrophysiological tests, retrograde labeling, and histomorphological analysis at 4 and 8 months postoperatively. RESULTS: Both ETS and ETE neurorrhaphies resulted in axonal regeneration and functional recovery of the recipient nerve but did not reach the level of intact controls. Significantly higher numbers of myelinated axons and labeled neurons giving regenerating fibers were found in group ETE compared with group ETS at both time points, consistent with the functional and electrophysiological recovery. Group ETS showed significantly smaller fiber diameter and thinner myelin thickness than group ETE at 4 months, but the difference became nonsignificant at 8 months. ETS neurorrhaphy had a very slight effect on the donor nerve, as determined electrophysiologically and histomorphologically. Sparsely distributed double-labeled neurons and relatively large amounts of single-labeled neurons contributing to reinnervation were found through double retrograde neuronal labeling in group ETS. Further quantitative analysis of the percentage of double-labeled neurons showed a pronounced tendency to decline from 19.8% at 4 months to 6.0% at 8 months postoperatively. CONCLUSION: Successful reinnervation after ETS neurorrhaphy could be achieved through both collateral sprouting and terminal sprouting, with the latter seeming to be the principal origin of motor nerve sprouting.