Turns-amplitude analysis of the electromyographic recruitment pattern disregarding force measurement. I. Method and reference values in healthy subjects.

We used turns-amplitude analysis to characterize the EMG recruitment pattern disregarding force measurement. The electrical muscle pattern of the brachial biceps (BB), abductor pollicis brevis (APB), medial vastus (MV), and anterior tibial (AT) muscles was analyzed during progressive increase in force from rest to maximum using the mean amplitude as an indicator of the force of the muscle. The following parameters were obtained on-line: the maximal ratio of turns to mean amplitude (peak-ratio, PR), the mean amplitude, and the number of time intervals (TI) between turns at PR and at near maximum force (NMF). The highest PR values were obtained in BB, the lowest in MV. Analysis of the distribution of the TI between turns at different degrees of voluntary contraction showed fewer spikes with short duration and small amplitude at high force compared with low force.     

Needle EMG of the tongue: motor unit action potential versus peak ratio analysis in limb and bulbar onset amyotrophic lateral sclerosis

OBJECTIVES—to find out if conventional andautomatic needle EMG of the tongue can be helpful in the diagnosis anddifferentiation of limb and bulbar onset amyotrophic lateral sclerosis.
METHODS—Motor unit action potential (MUAP)analysis and peak ratio interference pattern analysis were performed inthe right genioglossus muscle of 30 healthy subjects aged 30-81 years,10 patients aged 49-73 years with limb onset amyotrophic lateralsclerosis, and eight patients aged 52-75 years with bulbar onsetamyotrophic lateral sclerosis. Electrical activity was sampled viastandard concentric needle electrodes with a commercially available EMG recorder.
RESULTS—Normal mean (2SD) MUAP duration was 6.6 (1.5) ms. Normal mean (2SD) MUAP amplitude was 224 (97.4) µV. Normalmean (2SD) peak ratio (PR), turns/second (T/s), amplitude/turn (A/T),and time intervals (TI1, TI2, TI3) were 1.68 (0.56), 732 (303.9), 446 (180.3) µV, 2.62 (0.34), 2.31 (0.14), and 1.01 (0.50) respectively.Mean MUAP duration and amplitude were significantly increased in limb onset (P=0.0001 and P=0.013) and bulbar onset amyotrophic lateral sclerosis (P=0.0001 and P=0.017). Peak ratio indices stayed unchanged in limb onset amyotrophic lateral sclerosis but were significantly decreased (PR, T/s, A/T, TI1, and TI2) or increased (TI3) in bulbar onset disease. The sensitivity of the MUAP analysis was 70% in limband 75% in bulbar onset amyotrophic lateral sclerosis. The sensitivityof the peak ratio interference pattern analysis was 20% in limb and100% in bulbar onset amyotrophic lateral sclerosis. Subclinicalinvolvement of the tongue was found in 20% of the patients with limbonset amyotrophic lateral sclerosis and could be more accuratelyassessed with MUAP analysis than with automatic EMG.
CONCLUSIONS—both conventional and automaticneedle EMG of the tongue are valuable electrophysiological devices toassess the clinical and subclinical involvement of the tongue inpatients with limb and bulbar onset amyotrophic lateral sclerosis.

     

Demyelination and axonal degeneration in corpus callosum assessed by analysis of transcallosally mediated inhibition in multiple sclerosis.

OBJECTIVE: Following focal transcranial magnetic cortex stimulation (fTMS), inhibition of voluntary EMG activity in the ipsilateral first dorsal interosseus (FDI) muscle was studied, in order to assess the functional integrity of the corpus callosum in patients with multiple sclerosis (MS). METHODS AND RESULTS: Thirty-four patients suffering from definite MS and 12 healthy, age-matched normal subjects were examined. In mid-sagittal slices, 29 patients showed lesions within the truncus corporis callosi in T2-weighted MRI. In 20 patients, all areas (anterior, middle and posterior parts), in one both the anterior and posterior part, in 3 exclusively the anterior, in 4 the middle and in one the posterior area were affected. In 5 patients, lesions of corpus callosum were lacking. In normal subjects, fTMS elicited a transient inhibition (TI) of preactivated (50% of maximal force) isometric voluntary ipsilateral FDI muscle activity. Mean onset latencies of TI were 35.5+/-5.4 ms in right and 36.1+/-4.2 ms in left FDI. Mean duration of TI amounted to 23.0+/-8.4 ms for right and 24.6+/-8.4 ms for left FDI. In the MS group, TI latencies were significantly increased in 23 and TI durations in 16 cases, whereas a lack of TI was found in 5 patients bilaterally and in 6 unilaterally. In patients, mean onset latencies of TI were 40.4+/-13.8 ms in right and 43.3+/-14.4 ms in left FDI, TI duration amounted to 30.5+/-17.4 ms for right and 31.0+/-25.2 ms for left FDI. Increase of onset latencies and durations of TI were positively correlated with the summed area of lesions of corpus callosum in representative mid-sagittal MRI slices. Significant correlations between TI onset latencies and duration on the one hand, and central motor conduction latencies along corticospinal tracts (CML) on the other hand, were not found. CONCLUSION: The present investigation indicates that measurement of TI elicited by fTMS seems to be a sensitive method for an assessment of demyelination and axonal degeneration within corpus callosum in MS patients.     

Peak-ratio interference pattern analysis in the detection of neuromuscular disorders

Peak-ratio interference pattern analysis (peak-ratio method) is said to have a high sensitivity and to be independent of sex and age. This study was carried out to prove or disprove these findings. The peak-ratio method and qualitative motor unit action potential (MUAP) analysis were applied to the right brachial biceps and anterior tibial muscles of 44 healthy subjects, aged 23–87 years, 25 neuropathy patients, aged 21–83 years, and 29 myopathy patients, aged 19–70 years. Peak-ratio parameters were independent of sex and age. They tended to be lower in the anterior tibial muscle than in the brachial biceps muscle. Neuropathy patients typically showed decreased peak-ratio, short time intervals and increased amplitude/turn. Myopathy patients typically showed increased peak-ratio, turns/s and short time intervals. The sensitivity of the peak-ratio method was 72% for neuropathy patients and 59% for myopathy patients. The sensitivity of the peak-ratio method was similar to that of the MUAP analysis in neuropathy patients and higher than that of the MUAP analysis in myopathy patients. The specificity of the peak-ratio method was 80%. The peak-ratio method proved to be a valuable, supplementary electromyographic tool for the detection of neuromuscular disorders.     

脑干听觉诱发电位在面肌痉挛显微血管减压术中的应用价值

目的探讨脑干听觉诱发电位（BAEPs）V波潜伏期和（或）波幅的变化与面肌痉挛（HFS）显微血管减压术（MVD）后听力损失的应用价值。 方法选取中日友好医院神经外科自2015年9月至2019年8月行MVD治疗的HFS患者的临床资料，分析MVD始末BAEPs的V波潜伏期和波幅的变化以及手术前后听力状况的改变，听力学评估采用平均纯音听力阈值及言语识别率改变。根据美国耳鼻咽喉头颈外科学会分级方法，将术后患者听力分为听力未明显下降组和听力明显下降组。收集术中全程的BAEPs改变，并将BAEPs的V波术中改变分为：无显著异常，单纯V波潜伏期（LwV）延长>1.5 ms，单纯V波波幅（AwV）下降>50%，LwV延长>1.5 ms且AwV下降>50%，LwV延长>1.5 ms或AwV下降>50%，对5组分类模式下术后听力损伤程度与分组的相关性进行统计分析，并分析4组BAEPs改变对术后听力损伤的预测价值。 结果本研究纳入的1009例行MVD治疗的HFS患者中，943例患者听力未明显下降，66例患者术后听力异常，术中BAEPs监测波形无显著改变，术后出现听力下降5例（0.6%）；术中仅LwV延长>1.5 ms，术后出现听力下降4例（18.2%）；术中仅AwV降低>50%，术后出现听力下降19例（25.0%）；术中"LwV延长>1.5 ms且AwV降低>50%"，术后出现听力下降38例（64.4%）；术中"LwV延长>1.5 ms或AwV降低>50%"，术后出现听力下降61例（38.8%）。各组的阳性预测值比较，结果显示"LwV延长>1.5 ms且AwV降低>50%"最高；"LwV延长>1.5 ms或AwV下降>50%"组的敏感度最高；"LwV延长>1.5 ms且AwV下降>50%"组的特异度最强。 结论术中BAEPs监测可为MVD术者提供听力参考。术末V波潜伏期延长1.5 ms且波幅降低50%以上阳性预测值最高。术中根据BAEPs监测结果及时调整手术策略，可有效改善术后听力障碍的发生率。     

Diagnostic yield of analysis of the pattern of electrical activity and of individual motor unit potentials in myopathy.

The analysis of the pattern of electrical activity and of individual motor unit potentials in the same muscle both identified about 90% of 41 patients as having a myopathy. The pattern of electrical activity was analysed during a force which was a fixed fraction of maximum; individual motor unit potentials were analysed during weak effort. The two methods supplement each other as some of the patients were identified only by one or by the other of the two procedures. The parameter of the pattern of electrical activity which was most often abnormal was the ratio: numbers of turns to mean amplitude between turns.     

Correlates of disability in multiple sclerosis detected by transcranial magnetic stimulation

OBJECTIVE: To study the usefulness of corticospinally mediated excitatory responses and transcallosal inhibition (TI) elicited by transcranial magnetic stimulation (TMS) as a surrogate marker of disability in patients with different courses of MS. METHODS: Focal TMS of the motor cortex was performed in 118 patients with MS (96 with relapsing-remitting, 19 with primary progressive, and three with secondary progressive disease) who had an Expanded Disability Status Scale (EDSS) score between 0 and 6.5 and in 35 normal subjects. Central motor latencies (CML) and TI (onset latency, duration) were investigated. The Spearman rank correlation was used for statistical analysis. RESULTS: TMS disclosed prolonged CML in 52.5% and abnormal TI in 61% of the patients. In all patients the EDSS correlated with the frequency of abnormal TI (r = 0.58, p < 0.01) and abnormal CML (r = 0.51, p < 0.01). In patients with primary progressive MS (EDSS 1.5 to 6.5) the frequency of TI abnormalities correlated with EDSS (r = 0.65, p < 0.01) whereas CML did not. Delayed corticospinal responses in hand muscles always led to abnormal TI. CONCLUSIONS: The combination of central motor latencies and transcallosal inhibition evoked by transcranial magnetic stimulation yields objective data to estimate disease progression in MS as assessed by the EDSS.     

EMG power spectrum, turns-amplitude analysis and motor unit potential duration in neuromuscular disorders

The diagnostic value of power spectrum analysis of the needle EMG pattern at a force of 30% of maximum was compared to that of turns-amplitude analysis and to that of manual measurements of motor unit potential (MUP) duration in the brachial biceps muscle of 20 patients with myopathy and 11 patients with neurogenic disorders. In myopathy the power spectrum analysis had the same diagnostic value as the turns-amplitude analysis and MUP duration measurements and the 3 methods supplemented each other. In patients with neurogenic disorders the diagnostic value of the power spectrum analysis as well as that of the turns-amplitude analysis were lesser than that of MUP duration measurement. In diseased muscles the amount of high frequencies increased with increasing ratio of turns to mean amplitude while there was no relation between the power spectrum and the MUP changes. The results suggest that the power spectrum analysis of EMG can be used as a diagnostic tool in patients with neuromuscular disorders.     

Quantitative motor unit analysis: the effect of sample size.

This study of quantitative electromyography examines the influence of sample size on motor unit action potential (MUAP) tolerance limits, intertrial variability, and diagnostic sensitivity. We recorded 20 randomly selected MUAPs from the biceps muscle twice in 21 normal subjects, and once in 10 patients with myopathy. The 95% tolerance limits for mean total duration in normal subjects progressively narrowed from 6.6 to 14.2 ms for 5 MUAPs to 7.4 to 13.0 ms for 20 MUAPs. The 95% tolerance limits for intertrial variability were +/-22% for mean total duration of 20 MUAPs. Larger sample size had a greater effect on reducing intertrial variability than on narrowing 95% tolerance limits for amplitude and area. Quantitative EMG results for duration supported the presence of myopathy in 2 of 10 patients with analysis of 5 MUAPs, and 9 patients with analysis of 20 MUAPs. Although analysis of 5 potentials may be adequate for diagnosis occasionally, quantitative analysis of 20 MUAPs narrows tolerance limits, reduces intertrial variability, and improves diagnostic sensitivity.     

Impairment of respiratory function in late‐onset distal myopathy due to MATR3 Mutation

Introduction: Recently, mutations in the MATR3 gene were found to cause late‐onset distal myopathy. The frequency and impact of respiratory involvement are not clear. Methods: Respiratory parameters [maximum vital capacity (VCmax); forced expiratory volume (FEV₁); peak expiratory flow (PEF), postural drop of VCmax from sitting to supine, maximum inspiratory muscle pressure (PImax), mouth occlusion pressure after 100 ms (P 0.1), peak cough flow, and blood‐gas analysis] were monitored prospectively at baseline, and then 6 months and 12 months later in 8 patients with genetically confirmed MATR3 myopathy. Results: All patients showed involvement of respiratory function. Six of 8 reported exertional dyspnea. At the end of follow‐up, 5 of 8 had decreased VC, 7 of 8 had reduced PImax, and 5 of 7 had decreased partial pressure of oxygen (PO ₂). Within 12 months, respiratory parameters deteriorated non‐significantly. No patient required non‐invasive ventilation. Conclusions: There is a high risk of abnormal respiratory function with progressive worsening in MATR3 myopathy. Muscle Nerve 51 : 916–918, 2015     

The diagnostic yield of quantified electromyography and quantified muscle biopsy in neuromuscular disorders

Electromyography (EMG), histology, and histochemistry were related in 264 patients with neuromuscular disorders classified according to history and clinical and other laboratory findings. Electromyography and histological and histochemical abnormalities were divided in specific and nonspecific criteria. Specific histochemical criteria alone identified 28% of neurogenic lesions. Criteria of myopathy, obtained from the pattern of electrical activity during 30% of maximal effort, helped to delineate a myopathy when the only abnormality was an increased incidence of polyphasic potentials together with a pattern of full recuitment during maximal effort. Histology, histochemistry, or both, and EMG were concordant with clinical findings in 77% of 188 patients with myopathy and in 91% of 64 patients with neurogenic lesions. The electromyogram was concordant with the clinical classification in 87% of patients with myopathy and in 91% of patients with neurogenic impairment. The biopsy was in agreement with or contributed to the classification in 79% of patients with myopathy and in 92% of patients with neuropathy.     

Miyoshi-like distal myopathy with mutations in anoctamin 5 gene

Miyoshi myopathy is the most common form of recessive distal myopathy. Recessive mutations in the ANO5 gene have been recently identified in Northern Europe as a cause of non dysferlin-linked distal myopathy and limb girdle muscular dystrophy. We report here the first French cases of anoctamin 5 myopathy in 2 brothers presenting with a Miyoshi-like pattern. Comparing these patients with 12 other cases from the literature shows that all cases share a homogeneous clinical pattern, characterized by initial calf muscles involvement. Asymmetric muscle atrophy often precedes weakness. In this setting, high CK level and normal expression of dysferlin in muscle should lead to consider the diagnosis, which will be confirmed by ANO5 gene testing. The c.191dupA mutation, already reported as a founder mutation in Caucasian patients with anoctamin myopathies, was found in our family in a heterozygous state.     

GNE myopathy – A cross-sectional study on spatio-temporal gait characteristics

GNE myopathy is a rare, predominantly distal myopathy, involving mainly the lower limbs and presenting with gait disturbances. In this cross-sectional study gait evaluation of 23 (14 men) genetically confirmed GNE myopathy patients was done using Instrumented walkway analysis (GAITRite®) along with video gait capture. We recorded the topographical pattern of muscles involvement in lower limbs and correlated Functional Ambulation Profile-FAP and Medical Research council-MRC grading of lower limb scores with duration of illness. Early foot flat, foot drop gait with wider out-toed stance and higher perturbations with increased pressure at heel and decreased arm swing were noted. Muscle topography showed predominant weakness in ankle dorsi-flexors, flexor hallucis longus, extensor hallucis longus, hip adductors and knee flexors with stark sparing of quadriceps and relative sparing of hip- abductors, extensors, flexors and ankle plantar-flexors. Gait parameters in women were significantly more affected than men (p < 0.05) for the same duration of illness. FAP score and MRC grading of lower limb scores correlated significantly with duration of illness (p < 0.05). We observed that ankle dorsiflexors were affected earliest with sparing of quadriceps muscles in these patients.     

Impairment of callosal and corticospinal system function in adolescents with early-treated phenylketonuria: a transcranial magnetic stimulation study

The transcranial activation and the conduction properties of corticospinal and callosal neurons were investigated in 12 early-treated adolescents (aged 17.3, SD 3.5 years; range 14–27 years) with phenylketonuria (PKU) by focal transcranial magnetic stimulation (fTMS) of the motor cortex. The patients had no functionally relevant motor disturbances in daily life or on clinical testing. Corticospinally mediated excitatory (response thresholds, amplitudes, central motor latencies) and inhibitory [duration of postexcitatory inhibition (PI)] effects of fTMS were investigated in contralateral hand muscles. Transcallosal inhibition (TI) (onset latency, duration, transcallosal latency) of tonic electromyographic (EMG) activity was tested in ipsilateral muscles. Peripheral motor latencies were determined for responses elicited by magnetic stimulation over cervical nerve roots. Ten normal subjects served as controls. Since in all PKU patients, central and peripheral motor latencies were normal, no neurophysiological indication of a demyelination of corticospinal or peripheral motor fibres was found. However, cortical thresholds of corticospinally mediated responses were increased (52.1, SD 11.6% versus 35.0, SD 7.4% of maximum stimulator output; P < 0.05; n = 24 hands) and their amplitudes reduced (2.9, SD 1.4 mV versus 6.1, SD 1.5 mV, P < 0.05). The duration of PI was shortened (132, SD 53 ms versus 178, SD 57 ms; P < 0.05). TI was absent in 37.5% of the investigated hands or tended to be weak. When TI was present, its onset latencies (38.0, SD 3.6 ms versus 34.7, SD 3.3 ms) and transcallosal latencies were prolonged (18.5, SD 3.8 ms versus 14.8, SD 3.2 ms), while its duration was normal. These abnormal excitatory and inhibitory effects of fTMS suggest a reduced susceptibility of cortical excitatory and inhibitory neuronal structures compatible with a loss of neurons or a rarefication of their dendrites. Received: 1 December 1997 Received in revised form: 13 March 1998 Accepted: 27 April 1998     

Characteristics of the synchronous occipital and frontopolar spike phenomenon in Panayiotopoulos syndrome

Purpose: The synchronous appearance of an occipital and frontopolar spike (the Fp-O spike) is characteristic of Panayiotopoulos syndrome (PS). This phenomenon is also seen in various other types of epilepsy, particularly those that occur in childhood. Using dipole analysis and sequential mapping, we investigated the characteristics of the Fp-O spike observed in seven patients with PS and six patients with symptomatic localization-related epilepsy in childhood (SLE). Methods: We analyzed both one averaged spike and 20 manually selected successive individual Fp-O spikes for each patient through sequential topographical mapping with steps of 10 ms from 40 ms before to 40 ms after the negative maximum peak of each spike. For dipole analysis, a period of 40 ms before the maximum negative peak of the averaged spike in each patient was examined using equivalent current dipole localization software. Results: Sequential mapping revealed that occipital negative peaks preceded frontal negative peaks in all of the PS patients, as well as in two of the six SLE patients. The four remaining SLE patients did not exhibit preceding occipital peaks. In all of the patients with PS, representative dipole locations were in the posterior area, whereas in SLE patients they were scattered over more anterior areas. The estimated sources of the Fp-O and O spikes appeared to have the same position and orientation in the two PS patients. Conclusion: We conclude that Fp-O spikes in PS occur as the result of a rapid spread of epileptic activity from the posterior areas to the anterior areas of the brain. Fp-O spikes in PS patients show a uniform topographical pattern and dipole location, whereas those in other patients show more heterogeneity in these features. These findings support the homogeneity of PS and thus its designation as a syndrome.     

Conditioned stimulus duration in classical trace conditioning: test of a real-time neural network model.

In classical trace conditioning, the interstimulus interval (ISI) is equal to the conditioned stimulus (CS) duration plus the trace interval (TI), the interval between CS offset and unconditioned stimulus (US) onset. The Sutton-Barto-Desmond neural-network model of classical conditioning predicts that, with a sufficiently long TI, conditioning will be faster with a CS of relatively long duration than with one of shorter duration. This prediction is illustrated with simulations and tested with the rabbit nictitating membrane response. Animals were trained with a tone CS of 350- or 700-ms duration. The TI was fixed at 300 ms, so that the ISI for the two durations was 650 or 1000 ms, respectively. Another factor in the experimental design was tone intensity (63 or 83 dB). Consistent with the model's prediction, conditioning was faster with the longer ISI, but only with the louder tone. The results have implications for computational models of classical conditioning.     

The role of different EMG methods in evaluating myopathy.

For the diagnosis of myopathy, EMG may have an important role along with blood tests, muscle biopsies and genetic testing. This review evaluates different EMG methods in the diagnosis of myopathy. These include manual analysis of individual motor unit potentials and multi-motor unit potential analysis sampled at weak effort. At high effort, turns-amplitude analyses such as the cloud analysis and the peak ratio analysis have a high diagnostic yield. The EMG can seldom be used to differentiate between different types of myopathy. In the channelopathies, myotonia, exercise test and cooling of the muscle are helpful. Macro-EMG, single-fibre EMG and muscle fibre conduction velocity analysis have a limited role in myopathy, but provide information about the changes seen. Analysis of the firing rate of motor units, power spectrum analysis, as well as multichannel surface EMG may have diagnostic potential in the future. EMG is of great importance in the diagnosing of patients with myopathy, preferably a needle electrode and quantitative analyses should be used. A combination of a method at weak effort as well as a method at stronger effort seems optimal.     

Power spectrum analysis of the EMG pattern in normal and diseased muscles

The diagnostic value of analogue frequency analysis of EMG from patients with neuromuscular disorders has not been convincing. Using fast Fourier transformation it is today possible to obtain the EMG power spectrum on-line and with a better resolution. We examined the power spectrum of the EMG pattern of the brachial biceps muscle in 20 control subjects, 20 patients with myopathy, and 12 with neurogenic disorders. The electrical activity was sampled with a concentric needle electrode from 10 sites in each muscle. From each spectrum, mean power frequency, the power at 140 Hz, 1400 Hz, 2800 Hz and 4200 Hz relative to total power and the high/low ratio (1400/140) were obtained. The mean power frequency was higher at 10% than at 30% of maximal force. At a force of 30% of maximum the power spectrum analysis identified 55% and 64% of the patients with myopathy and neurogenic disorders, respectively. Although the diagnostic yield of the power spectrum analysis at a force of 10% of maximum was less than that at 30%, additional patients were identified at 10% increasing the diagnostic yield to 65% and 73% for patients with myopathy and neurogenic disorders, respectively. The best diagnostic parameters were the mean power frequency and the relative power at 1400 Hz.     

Prognosis in AZT myopathy.

The myopathy caused by zidovudine (AZT) appears to be common but is incompletely characterized, particularly regarding prognosis. Twenty patients with HIV infection developed a necrotizing myopathy while taking AZT for 9 to 30 months. Ten presented with myalgia and 17 with proximal muscle weakness. Serum CK was elevated in all (two to 11 times normal), and EMG suggested active myopathy in all but two. There were scattered granular degenerating fibers, with scant or no inflammation, in a pattern consistent with a toxic myopathy in all 18 patients biopsied. Three patients with an HIV-related inflammatory myopathy were distinguished by histologic differences. After stopping AZT (n = 15), myalgia promptly resolved (10 of 10). Strength improved more slowly with 12 of 15 regaining normal or nearly normal strength, but three have persistent weakness. CK returned to normal in 12 of 15, and follow-up EMG (n = 11) documented reduced fibrillation density in all 11 patients. These findings underscore the need for early diagnosis of this reversible myopathy.     

The diagnostic significance of large action potentials in myopathy

Electromyographic and histopathological studies were performed on 112 skeletal muscles in 101 subjects with myopathy. The diagnostic significance of large action potentials (LAPs) in myopathy was studied. LAPs were defined as those action potentials with a duration of over 13 ms and an amplitude of over 3 mV (peak to peak). The following results were obtained: Most muscles with LAPs showed the grouped atrophy of small fibers of neuropathic change in addition to myopathic findings. Even in myopathy most LAPs reflected neuropathic change, except in thyrotoxic myopathy. LAPs were not related to an increase of connective tissue increasing the impedance in volume conduction of the action potentials. LAPs were frequently seen in: progressive muscular dystrophy of limb-girdle type; scapuloperoneal dystrophy; distal myopathy; oculopharyngeal dystrophy; myotonic dystrophy; polymyositis; and thyrotoxic myopathy. Other types of myopathy had few LAPs. There were two types of progressive muscular dystrophy. One had LAPs frequently and the other, rarely. In myotonic dystrophy the muscles with LAPs showed scattered small angular fibers, possibly indicating neurogenic changes. Interstitial myositis had LAPs more frequently than parenchymatous polymyositis. The chronic phase of polymyositis had LAPs more frequently than the acute or subacute phases. In thyrotoxic myopathy the muscles with LAPs rarely showed definite neuropathic change histopathologically. Therefore, LAPs in thyrotoxic myopathy may not indicate denervation.