Optimal distance for segmental nerve conduction studies revisited

In 1972, Maynard and Stolov showed that the experimental error in calculating nerve conduction velocity (NCV) depends on errors of latency and distance measurements. Their data suggested that a minimum distance of 10 cm should be used when calculating NCV because of an increase in error >/= 25% at shorter distances. The object of this study was to reestablish the minimum distance using current technology. Twenty physicians measured the proximal and distal onset latencies of the same stored ulnar compound muscle action potentials, as well as the forearm skin distance. The mean and standard deviation of the errors in conduction time and distance were determined. A spreadsheet was constructed, determining the error in NCV for a variety of distances and NCVs. The average conduction time between proximal and distal stimulation was 3.23 ms, with a standard deviation of 0.09 ms. The mean distance measurement was 212.6 +/- 2.1 mm. The errors in NCV were significantly less than previously reported. The experimental error increased as distance decreased, reaching 20% with distances less than 6 cm. The latency error accounted for 71% of the total experimental error, as opposed to 90% in the previous study. With advances in electrodiagnostic equipment, NCV can reasonably be calculated at distances less than 10 cm, perhaps as low as 5-6 cm.     

Changes in nerve conduction velocity across the elbow due to experimental error

One diagnostic criterion for ulnar nerve mononeuropathy at the elbow (UNE) is a decrease in across-elbow nerve conduction velocity (NCV) > 10 m/s compared to the forearm segment. Distance and latency measurement errors are an inherent part of NCV calculations. Twenty electromyographers measured the latencies of stored ulnar compound muscle action potentials and measured the forearm and across-elbow distances along the ulnar nerve. Based on previously published equations, experimental error in NCV was calculated for various NCVs. The mean distances and standard deviations for the forearm and elbow segments were 212.5 +/- 2.1 mm and 86.7 +/- 4.2 mm, respectively. For an NCV of 55 m/s, a difference of 14 m/s between the two segments can occur from measurement error alone. Distance measurements about the elbow are fraught with interobserver errors rendering the resultant NCV of that segment of limited value as a sole criterion for the diagnosis of UNE.     

Carpal tunnel syndrome with normal nerve conduction studies

The utility of electrodiagnostic testing in the evaluation of carpal tunnel syndrome (CTS) has been questioned. We studied patients who met the clinical criteria for CTS and compared patients who had normal nerve conduction studies (NCS) with patients who had abnormal NCS. We found that 25% of the CTS patients without confounding neurologic disorders had normal NCS with median palmar nerve stimulation. Patients with abnormal NCS were older and heavier and had more clinical features of CTS. NCS results could not be predicted accurately from clinical features by use of logistic regression models. This was especially true in clinically borderline cases. NCS did not predict the outcome of conservative management. We concluded that NCS provide independent information in the evaluation of suspected CTS, especially when fewer clinical criteria are present, but that NCS are not helpful in predicting the outcome of nonsurgical management.     

The medial calcaneal nerve: Anatomy and nerve conduction technique

We report a new technique for studying conduction in the medial calcaneal nerve (MCN). Dissection of 14 cadaver feet revealed the optimal G₁ site to be one third of the way from the apex of the heel to a point midway between the navicular tuberosity and the prominence of the medical malleous. Seventy-two feet (36 healthy volunteers) were studied using surface stimulation of the tibial nerve 10 cm proximal to the G₁ surface electrode. Averaging technique was not required. Reference values (mean ± 2 SD) were determined for MCN onset latency (2.0 ± 0.3 ms), peak latency (2.5 ± 0.3 ms), onset conduction velocity (61 ± 11 m/s), peak conduction velocity (40 ± 5 m/s), baseline-to-peak amplitude (18 ± 6 μV), and maximum intrasubject side-to-side differences in these values (0.3 ms, 0.3 ms, 15 m/s, 5 m/s, and 17 μV, respectively). This study provides an easily performed, reproducible method for electrophysiologic evaluation of the MCN.© 1995 John Wiley & Sons, Inc.     

Lissencephaly with congenital muscular dystrophy and ocular abnormalities: cerebro-oculo-muscular syndrome

A Japanese male infant with lissencephaly, congenital muscular dystrophy (CMD), and ocular abnormalities is described. This patient represents features of the cerebro-oculo-muscular syndrome. Cranial computerized tomography revealed diffuse agyria, low density of the white matter, and hypoplasia of the cerebellar vermis. Brain histology suggested type II lissencephaly. These findings are correlated with other similar conditions, such as Walker-Warburg syndrome, Fukuyama-type CMD, and muscle, eye and brain disease.     

Reference data for commonly used sensory and motor nerve conduction studies

Introduction: The goal of this study was to generate reference data for a wide range of sensory and motor nerve conduction studies (NCSs) that are commonly used in routine electrodiagnostic practice. Methods: NCS data were collected from control subjects with a normal neurological examination and no known risk factors for or symptoms to suggest disease of the peripheral nervous system. Thirteen sensory and motor nerves were studied in the upper and lower limbs using standard recording techniques. Quantile regression was used to obtain estimates of the lower (e.g., 5th) percentiles for sensory and motor amplitudes and conduction velocities, as well as estimates of the upper (e.g., 95th) percentiles for distal motor latency and F‐wave latencies. Results: Reference data for sensory and motor amplitudes required adjustment for age; F‐wave latencies required adjustment for gender. Covariate adjustments were not required for other reference data. Data from N = 100 and N = 190 subjects permitted estimation of as low as the 4th and 2nd percentile, respectively, but further increases to N = 296 did not permit estimation of a more extreme percentile. Discussion: Efforts to develop reference data require careful selection of study subjects; sufficient sample size; adjustment for relevant covariates; and appropriate statistical methods for analysis. Reference data that cannot be estimated reliably due to absent potentials or data variability must be interpreted with caution. We present data for a range of clinically applicable reference percentiles, but judgment regarding which is most appropriate for diagnostic purpose awaits empiric evaluation in a disease population. Muscle Nerve 40: 772–794, 2009     

Dysmyelinating sensory-motor neuropathy in merosin-deficient congenital muscular dystrophy

A 20-year-old man with mild myopathy, external ophthalmoparesis, epilepsy, and diffuse white matter hyperintensity in the brain on magnetic resonance imaging had partial merosin deficiency in muscle and absent merosin in the endoneurium. Motor and sensory nerve conduction velocities were slow. Nerve biopsy showed reduction of large myelinated fibers, short internodes, enlarged nodes, excessive variability of myelin thickness, tomacula, and uncompacted myelin, but no evidence of segmental demyelination, naked axons, or onion bulbs. Thus, in congenital muscular dystrophy, merosin expression may be dissociated in different tissues, and the neuropathy is sensory-motor and due to abnormal myelinogenesis.     

AAEM minimonograph #34: polyneuropathy: classification by nerve conduction studies and electromyography

Electrodiagnostic evaluation of patients with suspected polyneuropathy is useful for detecting and documenting peripheral abnormalities, identifying the predominant pathophysiology, and determining the prognosis for certain disorders. The electrodiagnostic classification of polyneuropathy is associated with morphologic correlates and is based upon determining involvement of sensory and motor fibers and distinguishing between predominantly axon loss and demyelinating lesions. Accurate electrodiagnostic classification leads to a more focused and expedient identification of the etiology of polyneuropathy in clinical situations.     

Relationships between clinical data and quantitative EMG findings in facioscapulohumeral muscular dystrophy

Background and purposeIn recently published reports, electrophysiological findings were analysed, in some facioscapulohumeral muscular dystrophy (FSHD) cases without genetic disease confirmation. In several reports, some electrophysiological findings were described, not specific for myopathy. The aim of study was to analyse electrophysiological findings in a genetically homogeneous FSHD group to find possible relationships between electromyography (EMG) abnormalities and clinical symptoms.Material and methods37 patients with genetically proven FSHD (23 men and 14 women) aged 7–58 years (mean 28.8 years) were studied. Electromyographic examinations were done according to a uniform scheme for FSHD. Quantitative EMG examination was performed in vastus lateralis, tibialis anterior, deltoid and biceps brachii muscles.ResultsThere was no correlation between clinical features and electrophysiological findings. EMG confirmed myopathic changes in all patients with most advanced changes in tibialis anterior and deltoid muscles. Some of these changes were unspecific for myopathy and the degree of their intensity differed in particular muscles. The most advanced changes were observed in the tibialis anterior and deltoid muscles. The usefulness of the size index for myopathic processes assessment was confirmed. Analysis of so-called outliers for motor unit activity potential parameters did not show any new data for evaluation of the myopathic process. Myopathic changes in our material were not as advanced as those described in classical dystrophies. Histopathological examinations of skeletal muscle were normal in about 1/3 of patients.ConclusionsWe established that myopathic changes are clearly present in FSHD, with different degrees of intensity, most pronounced in tibialis anterior and deltoid muscles. There was no correlation between electrophysiological findings and clinical features. The size index provided the highest motor unit potential diagnostic sensitivity in FSHD.     

Genetic heterogeneity in three Chinese children with Fukuyama congenital muscular dystrophy

Three Chinese patients, two boys and one girl, were afflicted with the typical clinical, myopathological and neuroradiological findings of Fukuyama congenital muscular dystrophy (FCMD). Polymorphism analysis of our patients did not reveal the founder haplotype (138-192-147-183 in D9S2105-D9S2170-D9S2171-D9S2107) of Japanese FCMD, even though one patient was descended from Japanese ancestry. Full mutational analysis of the fukutin gene revealed that there is neither 3 kb insertion nor point mutation. These findings suggest genetic heterogeneity between Chinese and Japanese FCMD patients.     

Facioscapulohumeral muscular dystrophy presenting with isolated axial myopathy and bent spine syndrome

Several subtypes of facioscapulohumeral muscular dystrophy (FSHD) with atypical clinical presentation have been described. We report a new, distinct phenotype with progressive bent spine syndrome solely affecting the paraspinal muscles. Magnetic resonance imaging study of the lumbar spine revealed marked atrophy of the paraspinal muscles. The diagnosis was confirmed by DNA testing, which revealed shortened restriction fragments of the D4Z4 repeat on haplotype A in connection with a positive family history. Muscle Nerve 42:273–275, 2010     

Congenital fiber type disproportion in an adult: a morphometric and microchemical study

A 20-year-old man with marfanoid habitus had a history of congenital hypotonia and muscle weakness. Muscle biopsy showed extreme fiber type disproportion. There was total absence of Type 2B fibers. The severely hypertrophic Type 2A fibers showed twice the normal concentration of creatine phosphate at rest. These advanced morphometric, histochemical and biochemical changes may be interpreted as compensatory phenomena, which may explain the patient's pronounced functional improvement with advancing age.     

Patterns of nerve conduction abnormalities in POEMS syndrome

Primary acquired lumbar kyphosis of the adult, or bent spine syndrome, is probably secondary to late-onset muscle dystrophy preferentially involving the paravertebral muscles. In order to better define the extent of this myopathy, we compared spinal computerized tomography scans and muscle force, power, and fatigability, assessed by isokinetic tests, of the spinal erector and pelvic and shoulder girdle muscles in 23 patients with primary acquired lumbar kyphosis (20 women and 3 men, mean age 72.8 years) and 15 matched control subjects. Patients had decreased spinal and shoulder muscle density. Force, power, and work done were reduced in their paravertebral muscles, whereas in the scapular and gluteus medius muscles only work done after a series of 20 rapid movements showed a decrease. Primary acquired lumbar kyphosis in the adult may be considered as a late-onset girdle myopathy with subclinical involvement of the muscles of the pelvic and shoulder girdles.     

Critical reappraisal of referrals to electromyography and nerve conduction studies.

A large number of examinees referred to electromyographic (EMG) laboratories do not have symptoms or signs suggestive of a peripheral nervous system disorder, and the aim of the present study was to check this. All examinees evaluated by the author in a "general" EMG laboratory in the first 4 months of 2002 were included. Data on examinees, referral physicians and diagnoses, clinical symptoms and signs, and electrodiagnostic findings were statistically evaluated. Three hundred examinees, 42% men, were included. A neurological diagnosis was provided in 55% of referrals. Electrodiagnostic abnormalities were found in 45% of examinees. Using multivariate statistics, a positive effect of neurological referral diagnosis, history of paraesthesias and of weakness and sensory loss on examination, and a negative effect of history of pain on pathological electrodiagnostic findings were found. Except 20 patients with carpal tunnel syndrome, no patient with normal clinical examination had abnormal electrodiagnostic findings. Our study confirmed the inappropriateness of referrals to electrodiagnostic examination to screen patients for peripheral nervous disorders. We propose electrodiagnostic examination mainly of patients with unequivocal clinical signs of a peripheral nervous system lesion and of patients with typical symptoms of the carpal tunnel syndrome.     

Fibular motor nerve conduction studies and ankle sensorimotor capacities

Introduction: Nerve conduction studies provide information regarding the status of peripheral nerves, but relationships with sensorimotor capacities that influence mobility have not been defined. Methods: A secondary analysis was conducted on data from 41 older subjects (20 women and 21 men, age 69.1 ± 8.3 years), including 25 with diabetic neuropathy of varying severity and 16 without diabetes or neuropathy. Measurements included routine fibular motor nerve conduction studies and laboratory‐based determination of ankle inversion/eversion proprioceptive thresholds and ankle inversion/eversion motor function. Results: Independent of age, fibular amplitude correlated robustly with ankle inversion/eversion proprioceptive thresholds (R² = 0.591, P < 0.001), moderately with ankle inversion and eversion rates of torque generation (R² = 0.216; P = 0.004 and R² = 0.200; P = 0.006, respectively), and more strongly when fibular motor amplitude was normalized for body mass index (R² = 0.350; P < 0.001 and R² = 0.275; P = 0.001). Conclusions: Fibular motor amplitude was strongly associated with ankle sensorimotor capacities that influence lateral balance and recovery from perturbations during gait. The results suggest that nerve conduction study measures have potential for an expanded clinical role in evaluating mobility function in the population studied. Muscle Nerve 47: 497–503, 2013     

Renal dysfunction is rare in Fukuyama congenital muscular dystrophy

Background

The leading cause of death in patients with Fukuyama congenital muscular dystrophy (FCMD) is congestive heart failure or respiratory dysfunction, which is same as that in Duchenne muscular dystrophy (DMD). Recent studies reported that renal dysfunction is a common complication and an increasing cause of death in advanced DMD. It can be attributable to circulatory instability or inappropriate use of drugs for treating cardiac dysfunction.