Muscle & nerve
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Idiopathic adult-onset nemaline myopathy is a rare condition of unknown etiology that usually presents with proximal weakness. This case study reports a 60-year-old woman who presented with isolated type 2 respiratory failure secondary to bilateral hemidiaphragm weakness. A left vastus medialis muscle biopsy examined under light microscopy revealed appearances typical of nemaline myopathy. ⋯ Our patient's presentation highlights the importance of considering neuromuscular weakness as a cause of respiratory failure. Unless appropriate tests are performed-including a muscle biopsy, if indicated-specific neuromuscular diseases are easily missed. This can lead to inappropriate counseling and treatment.
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By determining the usefulness of motor unit number estimate (MUNE) and compound muscle action potential (CMAP) amplitude in patients with amyotrophic lateral sclerosis (ALS), we tried to find an effective way to stratify the disease stages. In all, 112 consecutive ALS patients were enrolled, among whom 73 were elicited in a longitudinal study. MUNE by the standard incremental technique, the average CMAP amplitude, total Medical Research Council (MRC) score, ALS-functional rating score (ALS-FRS), Appel ALS rating scale (AARS), and forced vital capacity (FVC) were performed at baseline and months 3, 6, and 12 after study entry. ⋯ The decrease in MUNE over the first 3 months was significantly greater than other measurements. We arbitrarily divided the patients into three stages: (1) rapid progression: the rate of change of MUNE and CMAP amplitude during the first 3 months exceeded 50%; (2) moderate progression: the rate of change of MUNE was greater than 50% but CMAP amplitude was less than 50%; (3) slow progression: the rate of change of both MUNE and CMAP amplitude were less than 50%. Comparing the rate of ALS-FRS descent per year using one-way ANOVA showed a significant difference among the three groups (P < 0.01).
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Case Reports
Myotonic dystrophy type 2 with focal asymmetric muscle weakness and no electrical myotonia.
Genetically proven myotonic dystrophy type 2 (DM2) was found in a 61-year-old woman with creatine kinase (CK) elevation and only isolated weakness of one triceps. There was no clinical or electrical myotonia. ⋯ Muscle biopsy showed nonspecific myopathic features and highly atrophic fibers with nuclear clumps. DM2 should be considered in patients with focal proximal weakness and abnormal EMG without myotonic discharges.
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The objective of this study was to determine if a transcranial magnetic stimulation (TMS) method of quantifying the degree to which the motor cortex drives the muscles during voluntary efforts can be reliably applied to the human knee extensors. Although the technique for estimating "cortical" voluntary activation (VA) is valid and reliable for elbow flexors and wrist extensors, evidence that it can be applied to muscles of the lower limb is necessary if twitch interpolation with TMS is to be widely used in research or clinical practice. Eight subjects completed two identical test sessions involving brief isometric knee extensions at forces ranging from rest to maximal voluntary contraction (MVC). ⋯ The amplitude of TMS-evoked twitch forces decreased linearly between 25% and 100% MVC (r(2) > 0.9), and produced reliable estimations of resting twitch and VA (ICC(2,1) > 0.85). The reliability and size of cortical measures of VA were comparable to those derived from motor nerve stimulation when the resting twitches were estimated on the basis of as few as three TMS trials. Thus, TMS measures of VA may provide a reliable and valid tool in studies investigating central fatigue due to exercise and neurological deficits in neural drive in the lower limbs.
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In 38 amyotrophic lateral sclerosis (ALS) patients and 28 controls, we performed motor unit potential (MUP) analysis in the C-6 and T-5 paraspinal and biceps muscles. In ALS cases, we found similar abnormalities in MUPs in paraspinal and limb muscles. Fasciculation potentials (FPs) were more frequent in biceps than in paraspinal muscles, but fibrillation potentials and positive sharp waves (fibs-sw) were equally frequent in all three muscles. These results confirm the value of paraspinal MUP analysis in the diagnosis of ALS.