Comparison of CMT1A and CMT2: similarities and differences

To evaluate the clinical and electrophysiological similarities and differences between two large groups of patients with Charcot-Marie-Tooth disease, i.e. CMT1A and CMT2, we performed a post hoc comparison of clinical and electrophysiological data.Most CMT1A and CMT2 patients had the classical CMT phenotype. Age of onset was significantly later in CMT2. Total areflexia was present in approximately half of the CMT1A patients whereas it was rare in CMT2. Foot deformities and weakness of knee extensor and foot dorsal flexor muscles were more frequent in CMT1A. Median nerve motor nerve conduction velocities (MNCV) were always less than 38 m/s in CMT1A patients, whereas this was also the case in 16% of the CMT2 patients. Sensory nerve conduction velocities showed less overlap. In both CMT1A and CMT2 CMAP and SNAP amplitudes were often reduced or not obtainable in the legs. In CMT1A, SNAP amplitude was more reduced and SNAP duration more prolonged than in CMT2.We conclude that there are no robust clinical signs or symptoms that differentiate between CMT1A and CMT2 patients. Electrodiagnostical studies show a length-dependent motor and sensory axonal dysfunction in both CMT-types. Additional SNAP and SNCV evaluation may be helpful in focusing molecular genetic analysis in the occasional case of CMT2 showing slow motor nerve conduction velocities overlapping with CMT1A values. The reduction of CMAP and SNAP amplitudes in CMT1A is probably a combined effect of demyelination and axonal dysfunction.     

Longitudinal conduction studies in hereditary motor and sensory neuropathy type 1

Motor conduction studies were performed serially in 10 patients, ages 10-62 years, with clinical and electrophysiological criteria of hereditary motor and sensory neuropathy type 1 (HMSN-1) over periods of 11-19 years. Median nerve conduction velocity (MNCV) and distal motor latency showed no significant change on serial studies. Mean median compound muscle action potential (CMAP) amplitude values, however, decreased 66% in 8 patients. Observed clinical progression in HMSN-1, over prolonged periods of time, was not associated with MNCV slowing. However, CMAP amplitude reduction, reflecting progressive axonal loss, correlated with clinical deterioration.     

Comparison of electrophysiological findings between CIDP and HMSN-1]

Chronic inflammatory demyelinating polyneuropathy (CIDP) and hereditary motor sensory neuropathy type 1 (HMSN-1) are representative myelinopathies. In order to differentiate changes in acquired and congenital demyelinating neuropathies, we studied electrophysiologically 9 patients with active phase of CIDP (36.0 +/- 17.6 years old; mean +/- SD) and 7 patients with genetically-proven HMSN-1 A (56.0 +/- 13.6 years old). Motor conduction studies demonstrated longitudinal uniformity in HMSN-1, contrariwise focal conduction block or conduction delay in CIDP. The mean median nerve conduction velocity in the forearm segment and the mean CMAP amplitude stimulated at the wrist were not different between CIDP and HMSN-1 group; 31.8 +/- 7.2 m/sec and 5.6 +/- 2.8 mV in CIDP, and 26.7 +/- 9.8 m/sec and 3.2 +/- 2.6 mV in HMSN-1, respectively. Upper extremity polyneuropathy index (PNI), a mean percentage of normal for 6 indices concerning to the velocity and latency over two nerves obtained by motor conduction studies, was equal and around 50% on the average in each group. Conduction blocks were presented in 7 patients with CIDP and only one patient with HMSN-1. No sensory nerve action potential was recorded in 6 out of 9 patients with CIDP, and in 6 out of 7 patients with HMSN-1. Intrafascicular neurography of the median nerve, stimulated at the wrist and recorded from intrafascicularly inserted microelectrode at the elbow, revealed irregular multiphasic waves which signify severe temporal dispersion. Maximum conduction velocity was similarly reduced to 48 m/sec in CIDP and 44 m/sec in HMSN-1 on the average, but in one patient with HMSN-1 it was maintained to 63 m/sec with conspicuous temporal dispersion of the waveform. Amplitude of the compound nerve action potential (CNAP) decreased more (p < 0.01) in HMSN-1 (26 +/- 11 micro V) than in CIDP (72 +/- 25 micro V). Temporal dispersion of CNAP was prominent in HMSN-1 than in CIDP. In conclusion, electrophysiological changes were more homogeneous in the longitudinal distribution but more heterogeneous in the cross-sectional distribution in HMSN-1 than in CIDP.     

Peripheral nerve function during hyperglycemic clamping in insulin-dependent diabetic patients

The influence of hyperglycemia on peripheral nerve function was studied in 9 patients with long-term insulin-dependent diabetes. Blood glucose concentration was raised 13.5 +/- 0.5 mmol/l (mean +/- SEM) within 15 min and kept approximately 15 mmol/l over basal level for 120 min by intravenous glucose infusion. Hyperglycemia was accompanied by increased plasma osmolality. Sensory and motor nerve conduction and distal motor latency in the ulnar nerve were determined before, immediately after induction of hyperglycemia, and again after 120 min hyperglycemia. Distal (5th finger - wrist) and proximal (wrist - elbow) sensory nerve conduction showed an insignificant increase as hyperglycemia was induced. During hyperglycemia mean distal sensory conduction decreased from 53.1 m/s to 50.4 m/s (P less than 0.05) and mean proximal sensory conduction decreased from 56.0 m/s to 54.2 m/s (P less than 0.01). A mean of distal and proximal sensory conduction increased (53.5 m/s vs 54.6 m/s) (P less than 0.05) as hyperglycemia was induced and decreased (54.6 m/s vs 52.3 m/s) (P less than 0.01) during clamping. Motor nerve conduction decreased insignificantly throughout the study. Mean distal motor latency decreased from 3.1 ms to 2.8 ms (P less than 0.005) immediately after induction of hyperglycemia. During hyperglycemia it increased from 2.8 ms to 3.1 ms (P less than 0.001). We conclude that acute induction of hyperglycemia in long-term diabetics seems to increase sensory conduction and decrease distal motor latency, while 120 min hyperglycemia seems to decrease sensory conduction and increase distal motor latency.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intracranial stimulation of the facial nerve: normative values with magnetic coil in 240 nerves

This study was aimed at defining normative values of latency and amplitude of the compound muscle action potential (CMAP) from the orbicularis oculi muscle, obtained by transcranial magnetic stimulation. We evaluated the dependence of latency and amplitude on the age of the subjects, in order to calculate cut-off values for each age decade. A total of 120 healthy normal subjects, aged 15–78 years, were studied. CMAP from the orbicularis oculi muscle, pars inferior, was excited by means of transcranial magnetic stimulation of the homolateral scalp. A suitable mathematical model was developed to evaluate the mean variation of the latency and amplitude of CMAP for each age decade in the studied population. Mean values were, respectively, 4.62±0.40 ms for latency and 4.17±0.72 mV for amplitude. We found an increase in latency of about 0.12 ms for every ten years, that became 0.15 ms if referring only to subjects over 20 years, and a decrease in amplitude of 0.18 mV each ten years. Normality interval values for the latency and amplitude were calculated for each age decade. Our data, obtained in a representative population for range of age of evaluated subjects, provide normality values and variability coefficients useful for future confronting works. Received: 20 September 2002 / Accepted in revised form: 6 December 2002 Correspondence to D. Cocito     

Intermediate Charcot–Marie–Tooth disease: an electrophysiological reappraisal and systematic review

Charcot–Marie–Tooth disease (CMT) is the most frequent form of inherited neuropathy with great variety of phenotypes, inheritance patterns, and causative genes. According to median motor nerve conduction velocity (MNCV), CMT is divided into demyelinating (CMT1) with MNCV below 38 m/s, axonal (CMT2) with MNCV above 38 m/s, and intermediate CMT with MNCV between 25 and 45 m/s. In each category, transmission may be autosomal dominant, autosomal recessive, or X-linked. The nosology of intermediate CMT is controversial because of concerns about electrophysiological delimitation. A systematic computer-based literature search was conducted on PubMed, using the following MeSH: (1) intermediate Charcot–Marie–Tooth; (2) X-linked intermediate Charcot–Marie–Tooth; and (3) X-linked Charcot–Marie–Tooth and electrophysiology. We retrieved 225 articles reporting X-linked CMT or intermediate CMT with electrophysiological information. After eligibility, 156 papers were used for this review. In assessing median MNCV, compound muscle action potential (CMAP) amplitudes were taken into account. In cases with attenuated CMAP and wherever possible, proximal median MNCV was used for accurate definition of conduction slowing in the intermediate range. In the vast majority of males with X-linked CMT associated with GJB1 mutation (CMTX1), median MNCV was intermediate. CMT associated with DRP2 mutation is another well-documented X-linked intermediate disorder. Autosomal dominant intermediate CMT (DI-CMT) encompasses 11 different types; six of them with assigned phenotype MIM number and the remaining five being unnumbered. Based on available electrophysiological information, we wonder if DI-CMTA should be reclassified within CMT2. Autosomal recessive intermediate CMT (RI-CMT) covers four numbered MIM phenotypes though, in accordance with reported electrophysiology, two of them (RI-CMTB and RI-CMTD) should probably be reclassified within AR-CMT2. We conclude that intermediate CMT is a complex inherited syndrome, whose characterization requires a specific electrophysiological protocol comprising evaluation of upper limb proximal nerve trunks when distal CMAP amplitudes are reduced, and that an updated version of MIM phenotype numbering is needed.     

Prevalence of peripheral neuropathy with insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is rare in Chinese children. There have been no reports on the prevalence of peripheral neuropathy in Chinese children with IDDM. This study aimed to determine prevalence of subclinical peripheral neuropathy in Chinese children with IDDM. Motor and sensory nerve conduction studies of both median, ulnar, peroneal, and tibial (motor nerves) and median, ulnar, and sural (sensory nerves) were performed in 38 children with IDDM (18 males, 20 females). The age was 4-21 years (mean = 12.7 years; median = 12 years, 6 months). The duration of diabetes was less than 5 years in 15, 5-10 years in 14, and more than 10 years in nine. Neurophysiologic evidence of subclinical peripheral neuropathy was present in 26 patients (68.4%) of which motor, sensory, or motor and sensory involvement was 26 (68.4%), eight (21.1%), and 26 (68.4%), respectively. Twelve (31.6%) and 14 (36.8%) children had mild and moderate degrees of peripheral neuropathy, respectively. Among the 26 children with abnormal nerve-conduction studies, two (7.7%) had symptoms of numbness and pain in the lower limbs. Thus, two children had symptomatic neuropathy and most (n = 24) had asymptomatic peripheral neuropathy. Two children had systemic hypertension, and one (3.8%) had laboratory evidence of early renal complications. Analysis of demographic and laboratory risk factors for the development of subclinical peripheral neuropathy revealed that the age of onset, duration of diabetes, level of hemoglobin A1c, triglyceride, cholesterol, serum creatinine, and urea, microalbumin/creatinine ratio, and urinary microalbumin excretion rate were significantly related to the development of subclinical peripheral neuropathy in specific nerves.     

节段性运动神经传导测定在慢性炎性脱髓鞘性多发性神经根神经病和腓骨肌萎缩症1型之间的差异

目的 探讨节段性运动神经传导测定在慢性炎性脱髓鞘性多发性神经根神经病(chronic inflammatory demyelinating polyradiculoneuropathy,CIDP)和腓骨肌萎缩症1型(Charcot-MarieTooth type1,CMT1)鉴别诊断中的价值.方法 收集16例CIDP和13例CMT1患者,进行节段性运动神经传导测定,比较两组远端运动潜伏期、运动神经传导速度,以及近端和远端比较复合肌肉动作电位波幅、面积和时限变化的差异.结果 CIDP和CMT1患者远端运动潜伏期分别为(5.6±3.4)、(9.3±2.1)ms(t=5.347,P=0.000),运动传导速度分别为(31.1±14.3)、(22.2±5.8)m/s(t=6.369,P=0.000),近端和远端比较波幅下降百分比M5o分别为29.7%和4.9%(Z=7.141,P=0.000).在CIDP患者,所有测定神经中40.3%(25/62)远端潜伏期正常,18.1%(26/144)的神经节段传导速度正常,而在CMT1中所有测定神经的远端潜伏期均延长,所有测定节段的传导速度均减慢.在CIDP患者29.2%的神经节段可见传导阻滞或异常波形离散,而在CMT1仅有3.0%的节段可见传导阻滞(x2=20.829,P=0.000).结论 当针对CIDP和CMT1进行鉴别时,如果节段性运动神经传导测定发现传导阻滞和异常波形离散、不同神经节段传导速度下降程度差别较大,可以支持 CIDP的诊断.     

Clinical utility of dorsal sural nerve conduction studies in healthy and diabetic children.

OBJECTIVE: Monitoring of the dorsal sural sensory nerve action potential (SNAP) is a sensitive method for detection of peripheral neuropathies. We tried to determine the normal dorsal sural nerve conduction values of the childhood population and assessed the clinical utility of this method in diabetic children who have no clinical sign of peripheral neuropathy. METHODS: In the study, 36 healthy and 27 diabetic children were included. In all subjects peripheral motor and sensory nerve studies were performed on the upper and lower limbs including dorsal sural nerve conduction studies. RESULTS: The dorsal sural SNAP mean amplitude was 8.24+/-3.08 microV, mean latency was 2.47+/-0.48 ms, mean sensory conduction velocity was 41.63+/-5.43 m/s in healthy children. Dorsal sural SNAPs were absent bilaterally in one diabetic patient. In the other 26 diabetic patients, the mean dorsal sural nerve distal latency was longer (2.93+/-0.63 ms, P = 0.004), mean SCV was slower than in healthy subjects (36.68+/-7.66 m/s, P = 0.005). However, dorsal sural nerve amplitude was not different between the groups. A dorsal sural nerve latency of more than 2.9 ms had a sensitivity of 50% and a specificity of 75%. A dorsal sural nerve velocity of less than 36 m/s had a sensitivity of 54% and a specificity of 92%. CONCLUSIONS: We designated the reference values of the dorsal sural nerve in healthy children. In addition, our findings suggest that dorsal sural nerve conduction studies may have value to determine neuropathy in the early stages in children with diabetes. SIGNIFICANCE: The dorsal sural nerve conduction studies in diabetic children may have value to determine the neuropathy in its early stages.     

Axonal Guillain-Barré syndrome associated with axonal Charcot-Marie-Tooth disease

We report the first case of axonal Guillain-Barré syndrome (GBS) associated with axonal Charcot-Marie-Tooth disease (CMT). A 30-year-old Japanese man, who had suffered leg atrophy and foot deformity since childhood, developed acute weakness in his four limbs following an upper respiratory tract infection. Nerve conduction studies showed low compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) amplitudes in all the nerves tested. Serial studies showed a rapid increase in CMAP amplitude, but no significant change in SNAP, which indicates that the acute event selectively involved motor axons and was superimposed on a baseline motor-sensory axonal neuropathy, probably CMT Type 2. Elevated serum IgG antibodies against GM1 and GM1b, an increase in CSF protein, and rapid clinical and electrophysiological recovery after plasma exchange support the diagnosis of a pure motor axonal form of GBS, acute motor axonal neuropathy. The association may be coincidental, but a particular susceptibility to axonal damage of CMT2 cannot be excluded.     

Anterior tibialis cmap amplitude correlations with impairment in CMT1A

Introduction: CMT1A is the most common form of Charcot‐Marie‐Tooth disease (CMT), a slowly progressive neuropathy in which impairment is length dependent. Fibular nerve conduction studies to the anterior tibialis muscle (AT) may serve as a physiological marker of disease progression in patients with CMT1A. The objective of this study is to determine whether the AT compound muscle action potential (CMAP) amplitude correlates with impairment in patients with CMT1A. Methods: We correlated AT CMAP amplitudes and impairment measured by the CMT Neuropathy Score (CMTNS) in a cross‐section of 121 patients with CMT1A and a subset of 27 patients with longitudinal data. Results: AT CMAP amplitudes correlated with impairment as measured by the CMTNS in cross sectional analysis. Longitudinal changes in the AT CMAP showed a strong inverse correlation with leg strength but not other components of the CMTNS. Conclusions: AT CMAP amplitude may serve as a useful outcome measure for physiological changes in natural history studies and clinical trials for patients with CMT1A. Muscle Nerve, 2013     

Peripheral nerve function during hyperglycemic clamping in healthy subjects

The influence of hyperglycemia with physiological hyperinsulinemia on peripheral nerve function was studied in 10 non-diabetic subjects. Blood glucose concentration was raised from 3.8 +/- 0.2 mmol/l (mean +/- SEM) to 17.1 +/- 1.4 mmol/l (mean +/- SEM) within 15 min and kept at this level for 120 min by intravenous glucose infusion. Sensory and motor nerve conduction velocity, and distal motor latency in the ulnar nerve were determined before, immediately after induction of hyperglycemia, and again after 120 min of hyperglycemia. Mean sensory nerve conduction velocity increased from 57.7 m/s to 59.5 m/s (P less than 0.005) immediately after induction of hyperglycemia, and after 120 min of hyperglycemia mean sensory nerve conduction velocity was 59.6 m/s (P less than 0.05). An insignificant increase was seen in motor nerve conduction velocity during hyperglycemia. Mean distal motor latency decreased from 3.1 ms to 3.0 ms (P less than 0.025) immediately after induction of hyperglycemia, and after 120 min of hyperglycemia distal motor latency was 2.9 ms (P less than 0.05). We conclude that short term hyperglycemia with physiological hyperinsulinemia seems to increase sensory nerve conduction velocity and decrease motor latency.     

Age‐related changes in motor unit number estimates in adult patients with Charcot–Marie–Tooth type 1A

Background: Charcot–Marie–Tooth disease type 1A (CMT1A) is known as a demyelinating hereditary neuropathy. Secondary axonal dysfunction is the most important determinant of disease severity. In adult patients, clinical progression may be because of further axonal deterioration as was shown with compound muscle action potential (CMAP) amplitude reductions over time. The motor unit number estimation (MUNE) technique may be more accurate to determine the number of axons as it is not disturbed by the effect of reinnervation. The purpose of this study was to investigate the number and size of motor units in relation to age in patients and controls. Methods: In a cross‐sectional design, we assessed arm and hand strength and performed electrophysiological examinations, including CMAP amplitudes and MUNE of the thenar muscles using high‐density surface EMG in 69 adult patients with CMT1A and 55 age‐matched healthy controls. Results: In patients, lower CMAP amplitudes and MUNE values were related to hand weakness. The CMAP amplitude and MUNE value of the thenar muscles were significantly lower in patients than in controls. CMAP amplitudes declined with age in controls, but not in patients. MUNE values declined with age in both patients and controls. Conclusions: The age‐dependent decrease in the number of motor units was not significantly different between patients with CMT1A and controls, indicating that loss of motor units in adult patients is limited.     

Electrophysiological assessment of central and peripheral motor routes to the lingual muscles.

Compound muscle action potentials (CMAPs) of the lingual muscles were recorded by especially devised bipolar surface electrodes placed on the tongue. Distinct responses were evoked in the tongue muscles by peripheral electrical stimulation of the hypoglossal nerve medial to the angle of the jaw and by transcranial magnetic stimulation of the motor cortex. With cortical stimulation during voluntary activation of the tongue muscles it proved easy to obtain responses with the characteristics of centrally evoked responses allowing reliable measurements of latencies and amplitudes. By contrast, responses from magnetic stimulation of the intracranial segment of the hypoglossal nerve were more difficult to obtain and the reproducibility was often not satisfactory. In a group of 20 healthy subjects the average distal motor latency of both sides from peripheral stimulation was 2.4 ms and the corresponding amplitude was 9.3 mV on the left and 8.6 mV on the right side (range 5.1-16.0 mV). Cortical stimulation gave responses with an average onset latency of 8.6 ms and 8.8 ms and an average amplitude of 1.8 mV and 2.6 mV on the left and right sides of the tongue respectively (range 0.7-5.6 mV). From this mean conduction times of 6.2 ms on the left and 6.4 ms on the right side (SD 1.0 ms) between cortex and mandibular angle and relative amplitudes from cortical stimulation as compared with the peripheral CMAP of 29% on the left and 21% on the right side (range 7%-66%) were calculated. In 16 patients it was possible to differentiate between a central (supranuclear) and a peripheral (intranuclear) site for the lesions of the motors routes to the lingual muscles and to show subclinical lesions in some cases. With a recording arrangement allowing selective unilateral recording of muscle activity from both sides of the tongue the assumed bihemispheric motor representation of the lingual muscles was confirmed.     

Central conduction time of magnetic brain stimulation in attention-deficit hyperactivity disorder

Twenty-seven children and adolescents aged 4 to 18 years, fulfilling the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria for attention-deficit hyperactivity disorder, were included in this study. The diagnosis was determined by a pediatric neurologist and a psychologist examined all 27 subjects with tests that included the Wechsler Intelligence Scale for Children-Revised (WISC-R) and reading, writing, handedness, personality, and anxiety scores. Subjects with histories of epilepsy, head injury, drug abuse, or psychotic disorders were excluded. Culturally based causes or emotional disorders were also excluded. Transcranial magnetic stimulation was performed on all subjects, with recording of the motor evoked potential at the biceps brachii. Central motor conduction time was calculated by cervical root stimulation. Due to shape variability, the amplitude of the motor responses was not measured in the study. The mean value of central conduction time in the subjects was very significantly increased (P < .001) compared to that in a group of normal controls, case-matched for IQ, age, and sex. A central motor conduction time greater than 12 ms indicates abnormality. A second finding in the subjects was the significant difference of central conduction time on the side-to-side stimulation (P = .03). These findings are correlated with delay in the maturation of the corticomotoneuronal system and might provide neurophysiologic data for diagnosis.     

Longitudinal studies of the duplication form of Charcot-Marie-Tooth polyneuropathy

This study presents a longitudinal comparison of motor nerve conduction velocities (MCVs) in patients with Charcot-Marie-Tooth type 1A with proven duplication of a segment of chromosome 17p11.2p12. Results were compared for 8 CMT1A duplication patients from one family whose MCV measurements were taken 22 years apart (1967 and 1989). Measurements from a total of seven median motor and five peroneal motor MCVs were compared. Median MCVs showed a slight reduction that averaged 2.2 m/s, and peroneal MCVs showed an average decrease of 3.0 m/s. In addition, mild objective increase in limb weakness was seen in only 1 of 8 patients and subjective symptoms of gradual worsening of leg strength were noted in half the patients over the same period. In this study of a small group of CMT1A patients with proven segmental duplication of chromosome 17p11.2p12, the motor conduction velocities and clinical motor exam did not change significantly over 22 years. © 1996 John Wiley & Sons, Inc.     

Cervical nerve root stimulation. Part II: findings in primary demyelinating neuropathies and motor neuron disease.

OBJECTIVE: Cervical nerve root stimulation (CRS) allows the assessment of conduction in the proximal segments of motor fibers destined to the upper extremities, which are not evaluated by routine nerve conduction studies (NCS). Since many primary demyelinating polyneuropathies (PDP) are multifocal lesions may be confined to the proximal nerve segments. CRS may therefore increase the yield of neurophysiologic studies in diagnosing PDP. METHODS: We reviewed clinical and neurophysiologic data from 38 PDP patients and compared them to 35 patients with motor neuron disease (MND), and 21 healthy controls (HC). RESULTS: Mean onset-latency was significantly prolonged in PDP patients. The optimal onset-latency cutoff necessary to distinguish PDP from MND and controls was 17.5 ms for the abductor pollicis brevis (APB) and abductor digiti minimi (ADM), and 7 ms for Biceps and Triceps. Mean reduction in proximal to distal CMAP amplitude to APB and ADM was significantly greater in PDP patients, with an optimal cutoff in proximal to distal CMAP amplitude reduction necessary to distinguish PDP from MND and HC being 45%. CONCLUSIONS: CRS is effective in distinguishing PDP from MND and HC based on prolonged onset latency and conduction block criteria. SIGNIFICANCE: CRS may increase the diagnostic yield in cases where demyelinating lesions are confined to the proximal peripheral neuraxis.     

Electrophysiological analysis of changes in peripheral nervous system in multiple sclerosis]

In order to analyse the peripheral disturbances repetitive stimulation test (RNS Test) and nerve conduction studies were done in 33 patients, 19 women and 14 men (mean age 38.2 years), with at least probable diagnosis of multiple sclerosis. In RNS Test the mean CMAP amplitude was significantly lower in comparison to the control group without any difference after 30 seconds of effort. Significant decrementing response was revealed at low rate of stimulation (2Hz) and incrementing response during tetanic stimulation. Significant lower mean amplitude of M wave in all investigated nerves was found in motor nerve conduction velocity test. Abnormal mean distal latency and motor conduction velocity were less common. The mean results of sensory conduction velocity test were similar to the control group.     

腓骨肌萎缩症1A型的临床、神经电生理和疾病基因突变分析

目的　观察腓骨肌萎缩症 (CMT) 1A型的临床、神经电生理特点和疾病基因的突变分析。方法对一CMT家系中 9个成员进行详尽的临床检查、疾病基因突变分析 ,对先证者进行神经电生理检查和神经肌肉活检。结果　本家系中 5人发病 ,符合常染色体显性遗传模式 ,除 1例患者无临床症状外 ,其余 4例均在2 0岁前起病。临床特点为进行性四肢远端肌无力、肌萎缩 ,末梢型感觉障碍 ,腱反射减弱或消失 ,足部畸形(高弓足 )。神经电生理检查示运动和感觉神经传导速度减慢。基因突变分析发现 17号染色体短臂 11 2区(17p11 2 )包含周围髓鞘蛋白 (PMP) 2 2基因的正向串联重复突变。结论　CMT1A型是CMT最常见类型 ,多于儿童期或青少年期起病 ,表现为进行性四肢远端肌无力、肌萎缩 ,腱反射减弱或消失。神经电生理特点为运动神经传导速度均一性减低 (<38m/s)。 17p 11 2区包含PMP 2 2基因在内的 1 5Mb(偶尔 <1 5Mb)的正向串联重复突变是CMT 1A最主要的突变型。     

Effect of reference electrode position on the compound muscle action potential (CMAP) onset latency

Compound muscle action potential (CMAP) onset latency is interpreted to reflect the arrival time at the muscle of impulses in the fastest-conducting motor nerve fiber. However, we have observed that the position of the reference or indifferent electrode (E2) affects CMAP onset latency. Motor nerve conduction studies (NCS) of the median, ulnar, and deep ulnar motor (DUM) nerves on 20 normal hands were performed using both traditional bipolar and experimental monopolar (referenced to the contralateral hand) montages. As the position of E2 was altered, the CMAP onset latency varied 0.1-0.5 ms for the median NCS, 0.1-0.3 ms for the ulnar NCS, and 0.1-1.5 ms for the DUM NCS. This study demonstrates that E2 recorded potentials are significant and vary with positioning, affecting motor onset latency. This has implications both for reference values and the physiologic interpretation of the CMAP waveform.