Showing papers in "Muscle & Nerve in 1979"
TL;DR: The utility of this histochemical method and the existence of persons deficient in AMPDA through the use of an unrelated assay technique are confirmed and the lack of enzyme activity is not associated with any inhibitory activity in the muscles of patients with this disorder.
Abstract: Myoadenylate deaminase (adenosine monophosphate deaminase--AMPDA) was recently shown to be deficient in a group of patients by use of a histochemical and biochemical method based on the elaboration of ammonia by this enzyme as it deaminates 5' AMP. We have confirmed the utility of this histochemical method and the existence of persons deficient in AMPDA through the use of an unrelated assay technique. The lack of enzyme activity is not associated with any inhibitory activity in the muscles of patients with this disorder. The clinical diversity of these patients suggests that this lack may represent a normal variant or a subclinical state rather than an actual disease. The occurrence of AMPDA deficiency in both sexes points to possible autosomal inheritance.
179 citations
TL;DR: Aging in the rodent is accompanied by a progressive loss of skeletal muscle fibers and the muscle twitch also becomes slower, probably as a result of fibertype conversion from “fast‐twitch” to “slow‐twitch.”
Abstract: Aging in the rodent is accompanied by a progressive loss of skeletal muscle fibers. The muscle twitch also becomes slower, probably as a result of fiber-type conversion from "fast-twitch" to "slow-twitch." The loss of muscle fibers precedes signs of obvious weakness and appears to involve the loss of entire functioning motor units. In the mouse, this loss of motor units correlated with a loss of axons from the innervating nerve trunks.
169 citations
TL;DR: Five volunteer subjects held isometric handgrip contractions at specific submaximal tensions until the required tension could no longer be maintained, and sustained contractions showed that strength declined linearly at all tensions.
Abstract: Five voluntee subjects held isometric handgrip contractions at specific submaximal tensions until the required tension could no longer be maintained. At the start of those contractions, the amplitude of the surface electromyogram (EMG) was linearly related to the tension exerted; the amplitude of the EMG increased linearly throughout these substained contractions by a constant amount--about 30% of the maximum. During sustained contractions, brief, intermittent maximal efforts showed that strength declined linearly at all tensions. At 25% maximal voluntary contraction (MVC), there was a linear fall in the EMG amplitude associated with the brief maximal efforts, but the fall in strength was more rapid than the fall in EMG amplitude. At 70% MVC, there was no fall in the EMG amplitude in response to the brief maximal efforts, while the muscle strength fell linearly.
116 citations
TL;DR: The extent of F chronodispersion of the deep peroneal nerve did not exceed 7.5 msec in control subjects, while it was longer than this value in all uremic patients studied, and may prove to be a useful diagnostic tool for cases in which traditional electrophysiologic measurements are normal.
Abstract: We have introduced the term F chronodispersion to denote the scatter or dispersion of the relative latencies of statistically significant numbers of consecutively recorded F waves. Five patients with chronic renal failure and five control subjects were studied. The two groups were matched for age, sex, proximal and distal motor conduction velocity, and latency of fast F waves plotted against distance traveled. We found that the extent of F chronodispersion of the deep peroneal nerve did not exceed 7.5 mscec in control subjects, while it was longer than this value in all uremic patients studied. Measurements of this type may prove to be a useful diagnostic tool for cases in which traditional electrophysiologic measurements are normal.
87 citations
TL;DR: Five out of 12 lateral femoral cutaneous nerves, removed at routine autopsies, showed pathologic changes in myelinated nerve fibers in the vicinity of the inguinal ligament that may be implicated in the production of some of the symptoms of meralgia paresthetica.
Abstract: Five out of 12 lateral femoral cutaneous nerves, removed at routine autopsies, showed pathologic changes in myelinated nerve fibers in the vicinity of the inguinal ligament. These changes included both local demyelination and Wallerian degeneration, particularly affecting the fibers with the largest diameters. The presence of polarized internodal swellings on single nerve fibers from two specimens suggested that mechanical factors were involved in pathogenesis. Endoneurial vascular thickening confined to the region of the inguinal ligament was also seen and may be implicated in the production of some of the symptoms of meralgia paresthetica (MP).
67 citations
TL;DR: Axonal transport studies demonstrated a significant increase in the amount of acetylcholinesterase transported in an orthograde direction in the sciatic nerves of alcohol‐exposed rats, and indicated no change in the transport of choline acetyltransferase or in the specific binding of colchicine by neurotubulin.
Abstract: A chronic high alcohol intake was induced in rats through the use of two procedures: the schedule-induced polydipsia technique and the liquid diet technique Rats consumed 11-12 g of ethanol per kilogram body weight per day for 16 to 18 weeks Morphologic evidence of a mild distal axonal neuropathy in the ventral caudal nerve was proposed The red blood cell transketolase levels were normal, indicating that the rats were not deficient in thiamine and suggesting that the axonal degeneration was due to the direct toxic effect of alcohol Axonal transport studies demonstrated a significant increase in the amount of acetylcholinesterase transported in an orthograde direction in the sciatic nerves of alcohol-exposed rats, and indicated no change in the transport of choline acetyltransferase or in the specific binding of colchicine by neurotubulin
63 citations
TL;DR: The possibility that malignant hyperthermia may be initiated by this abnormal depolarization of skeletal muscle by halothane is suggested.
Abstract: Halothane, at clinical concentrations, depolarizes the plasma membrane of skeletal muscle from Poland China pigs susceptible to malignant hyperthermia but does not affect the resting membrane potential of muscle from normal poland China pigs, mice, or frogs. The depolarization is reduced or partially reversed in the presence of dantrolene sodium. We suggest the possibility that malignant hyperthermia may be initiated by this abnormal depolarization of skeletal muscle by halothane.
60 citations
TL;DR: In this article, a patient with systemic lupus erythematosus (SLE) was treated with chloroquine therapy for four years after the onset of her illness.
Abstract: A patient with systemic lupus erythematosus (SLE) was treated with chloroquine therapy for four years after the onset of her illness. Nine years after cessation of chloroquine, muscle weakness developed as part of the SLE. Four muscle biopsies performed for diagnostic purposes revealed varying degrees of inflammatory change as well as distinctive cytosomes with curvilinear profiles (CCPs). These CCPs were identical to those reported in Batten disease, a degenerative disorder of children which has a clinical course different from SLE. The CCPs seen in this case of SLE are thought to result from the effect of chloroquine on membrane systems within muscle cells. This report calls attention to the fact that CCPs are not unique to Batten disease but may also occur in muscle of SLE patients treated with chloroquine.
57 citations
TL;DR: There are discrepancies in the classification of neuromuscular diseases affecting infants, and in some instances a single diagnosis seems to include patients with quite separate illnesses, whereas other patients with seemingly identical diseases have been given different diagnoses.
Abstract: The definition of neuromuscular diseases affecting infants has depended on factors as various as the rate of progression of the illness, the clinical picture, and, recently, the morphologic peculiarities in the muscle biopsy. A review of the literature suggests that there are discrepancies in the classification of such illnesses, no matter what system is used. In some instances, a single diagnosis seems to include patients with quite separate illnesses, whereas other patients with seemingly identical diseases have been given different diagnoses.
56 citations
TL;DR: The excessive accumulation of triglyceride in different tissues and in the progeny of cells in tissue culture suggests a genetic error of lipid metabolism.
Abstract: A 41-year-old man had ichthyosis, ectropion, steatorrhea, and slowly progressive proximal limb weakness. Biopsies showed abnormal lipid accumulation in muscle, liver, skin, leukocytes, and gastric mucosa. Lipid storage was particularly marked in cultures of skin and muscle, and it increased in subsequent cell generations. By electron microscopy, the lipid globules showed no limiting membranes. The stored lipid was identified by thin-layer chromatography as triglyceride; there was no excess of cholesterol or cholesteryl esters. Muscle carnitine concentration and activities of carnitine palmityltransferase and acid lipase were normal; 14CO2 production from labeled palmitate in leukocytes was not impaired. The excessive accumulation of triglyceride in different tissues and in the progeny of cells in tissue culture suggests a genetic error of lipid metabolism.
56 citations
TL;DR: On the basis of the PK and CK measurements, only 16 of 24 possible carrier mothers were likely to be DMD carriers, implying that the other 8 were non‐carrier mothers of new mutant sons.
Abstract: The incidence of elevated serum creatine kinase (CK) and pyruvate kinase (PK) activities was compared in 20 definite carriers of Duchenne muscular dystrophy (DMD), 47 possible carriers, and 42 female controls. When adult age was not regarded as a variable, 70% of the definite carriers had elevated PK, 55% had elevated CK, and 75% had elevated PK or elevated CK or both, 38% of the possible carriers had elevated PK, 19% had elevated CK, and 40% had elevated PK or elevated CK or both. The detection efficiency of the CK test was influenced by the age of the subjects: the upper normal limit of serum CK in the adult controls was at the minimum between 21 and 35 years of age, and CK activity in some carriers declined from elevated to normal levels with increasing age. With these considerations, 70% of definite carriers had elevated CK and 80% had elevated PK and/or CK; 34% of the possible carriers had elevated CK and 43% had elevated PK and/or CK. On the basis of the PK and CK measurements, only 16 of 24 possible carrier mothers were likely to be DMD carriers, implying that the other 8 were non-carrier mothers of new mutant sons.
TL;DR: Ulastructural studies of muscle and nerve biopsies showed the presence of intracytoplasmic inclusions, primarily in Schwann cells, muscle fibers, and endothelial cells, that were polymorphic and varied from one cell type to another.
Abstract: Perhexiline maleate therapy may produce a polyneuropathy as well as other side effects in man. The Schwann-cell origin of the neuropathy is demonstrated by morphologic studies. Ultrastructural studies of muscle and nerve biopsies showed the presence of intracytoplasmic inclusions, primarily in Schwann cells, muscle fibers, and endothelial cells. These inclusions were polymorphic and varied from one cell type to another. They were frequently associated with calcium deposits, and their structure suggested a lysosomal origin. It was possible experimentally to reproduce similar inclusions in mice. Furthermore, numerous tubular aggregates were observed in intoxicated mouse muscle fibers.
TL;DR: The rate of increase in receptor destruction due to antigenic modulation observed in vitro appears sufficient to account for the extent of receptor loss observed in vivo, and endocytosis of antibody cross‐linked receptors may be a rate‐limiting step common to antigenics modulation in vitro and in vivo.
Abstract: Immunization of groups of rats with 0.1- 100 microgram of acetylcholine receptor (AChR) purified from the electric organ of Torpedo californica resulted in dose-dependent (1) loss of acetylcholine receptor from the rats' muscles, (2) binding of antibodies to many of the receptors remaining in muscle and (3) production of antibodies in serum capable of cross-reacting with receptor solubilized from rat muscle. Addition of antibodies from rats immunized with electric organ acetylcholine receptors to muscle cells in culture caused loss of receptor by accelerating the rate of receptor degradation. Monovalent antibody fragments did not accelerate degradation unless antiantibody was added to cross-link the monovalent antibody fragments bound to receptors. This indicates that cross-linking of receptors by antibody molecules triggers accelerated receptor degradation, leading to receptor loss. The rate of increase in receptor destruction due to antigenic modulation observed in vitro appears sufficient to account for the extent of receptor loss observed in vivo. Endocytosis of antibody cross-linked receptors may be a rate-limiting step common to antigenic modulation in vitro and in vivo.
TL;DR: It is suggested that all fibers were capable of generating action potentials when hyperpolarized, and that allaction potentials were blocked by tetrodotoxin, suggesting the relative intactness of the regenerative sodium conductance mechanism in the disease studied here.
Abstract: Electrophysiologic properties of biopsied normal and diseased intercostal muscle fibers were examined using intracellular microelectrode techniques The resting potentials of all diseased muscle fibers were found to be depolarized Those from Duchenne dystrophy patients showed the largest depolarization, followed by those from patients with myotonic muscular dystrophy, myotonia congenita, and motor neuron disease All of the diseased fibers except those from myotonia congenita patients demonstrated an imparied ability to generate action potentials In the latter fibers, the higher-than-normal membrane resistance was associated with hyperexcitability When the membrane was hyperpolarized to the normal range, however, action potential characteristics in all fibers were near normal, except in motor neuron disease All action potentials were blocked by tetrodotoxin These findings--ie, that all fibers were capable of generating action potentials when hyperpolarized, and that all action potentials were blocked by tetrodotoxin--suggest the relative intactness, in the disease studied here of the regenerative sodium conductance mechanism
TL;DR: It is concluded that, for any patient suspected of having a myopathy, electromyographic examination should include the paraspinal muscles, and the distribution of fibrillation potentials in different muscles is discussed.
Abstract: Forty patients with polymyositis or dermatomyositis underwent detailed electromyographic evaluation. The paraspinal muscles of all patients were examined, as were several extremity muscles. The distribution of fibrillation potentials (FPs) in different muscles is discussed. FPs were most frequent in paraspinal muscles. We conclude that, for any patient suspected of having a myopathy, electromyographic examination should include the paraspinal muscles.
TL;DR: The histochemical and fine structural profiles of human intrafusal muscle fibers were studied and appear to be analogous to the two types of nuclear bag fiber identified in animal spindles and are considered to have different roles in spindle function.
Abstract: The histochemical and fine structural profiles of human intrafusal muscle fibers were studied. Spindles were located in freshly frozen specimens taken from biopsied normal external intercostal muscles, and periodic 10- and 50-mum-thick cross sections were processed alternately for enzyme histochemical and electron microscopic examination. Nuclear bag fibers were of two types, bag1 and bag2, histochemically, and they displayed two distinct types of ultrastructure. Nuclear chain fibers were histochemically and ultrastructurally homogeneous. Regional differences in enzymatic staining and ultrastructure occurred along individual intrafusal fibers. Human bag1 and bag2 fibers appear to be analogous to the two types of nuclear bag fiber identified in animal spindles and are considered to have different roles in spindle function. The presence of three types of intrafusal fibers should be taken into account when studying spindle abnormalities in human neuromuscular disorders.
TL;DR: In five patients with unilateral wasting of the hand muscles as a result of a cervical rib and band, F waves were recorded from the hypothenar muscles following stimulation of the ulnar nerve at the wrist, suggesting recovery of a local conduction block in the proximal part of the nerve.
Abstract: In five patients with unilateral wasting of the hand muscles as a result of a cervical rib and band, F waves were recorded from the hypothenar muscles following stimulation of the ulnar nerve at the wrist. Twelve healthy control subjects were also examined. F-wave latency was consistently increased in the affected hands of the patients, compared with results from the unaffected and control hands. This increase persisted after removal of the cervical band in four patients and was thought to be mainly due to degeneration of fast-conducting fibers. In the fifth patient, F-wave latency decreased after operation, suggesting recovery of a local conduction block in the proximal part of the nerve.
TL;DR: The treatment‐induced enhancement of the specific twitch tension was more pronounced in the gastrocnemius muscles than in the soleus muscles, suggesting that the difference in response to steroid treatment may reflect structural and functional difference in fast‐ and slow‐muscle membrane systems.
Abstract: In an attempt to determine whether chronic glucocorticoid treatment affects speed- and strength-related properties of fast-twitch muscle and slow-twitch muscle, in-situ contractile properties of soleus and gastrocnemius muscles were measured in rats after 14 days on a regiment of triamcinolone acetonide injected at a dosage of 2 mg/kg/day. No effects on contractile speed or strength were noted for either muscle. The time to peak tension in soleus muscle was significantly longer in the treated group (43.0 +/- 1.0 msec) than in the control group (38.7 +/- 0.7 msec); however, this was attributed to a prolongation of "active state" duration, as suggested by the fact that treated muscles also showed significantly elevated twitch-tetanus ratios. The treatment-induced enhancement of the specific twitch tension was more pronounced in the gastrocnemius muscles (198% +/- 19% of control) than in the soleus muscles (153% +/- 9% of control). The difference in response to steroid treatment may reflect structural and functional differences in fast- and slow-muscle membrane systems.
TL;DR: Microscopic examination confirmed the presence of edema as predicted by the sorbitol theory, which is often invoked to explain the pathogenesis of diabetic neuropathy.
Abstract: Edema and increased endoneurial fluid pressure developed in peripheral nerves of rats that received a diet containing 40% galactose during a study of the role of sugar alcohols in producing neuropathy. Fluid pressure was elevated starting in the third month and progressed to a fivefold increase over control values by the fifth month. Microscopic examination confirmed the presence of edema as predicted by the sorbitol theory, which is often invoked to explain the pathogenesis of diabetic neuropathy.
TL;DR: Net muscle protein degradation in betamethasone‐treated and control rabbits indicate that both type 1 and type 2 muscle fiber proteins are degraded several times faster in the corticosteroid‐treated group, which suggests that a compensatory mechanism exists for those type 2 and mixed fiber type muscles which have increased degradation but do not undergo wasting.
Abstract: Corticosteroid myopathy was studied in young, mature New Zealand white rabbits given daily injections of betamethasone (0.3 mg/kg body weight/day) for two weeks. Control rabbits were pair-fed and received saline injections. Bethamethasone treatment caused significant wasting of type 2 gluteus medius and psoas muscles but did not cause any atrophy of type 1 soleus and gluteus minimus muscles. The Mg2+- and Ca2+-activated myofibrillar ATPase activities of the corticosteroid-treated rabbits did not differ from controls despite a 30% reduction in muscle wet weight and pronounced reduction in cross-sectional area of fibers. SDS-polyacrylamide gel electrophoresis profiles of myofibrillar proteins did not differ quantitatively or qualitatively between experimental and control rabbits. Studies of net muscle protein degradation (using 3H-leucine) in betamethasone-treated and control rabbits indicate that both type 1 and type 2 muscle fiber proteins are degraded several times faster in the corticosteroid-treated group. This suggests that a compensatory mechanism exists for those type 1 and mixed fiber type muscles which have increased degradation but do not undergo wasting.
TL;DR: Treatment with gangliosides of the bovine brain cortex seemed to improve the excitability of the surviving motor units and to encourage recovery of neuromuscular trophic control, but it did not affect the nerve conduction velocity or the contractile properties of the denervated muscle.
Abstract: Short-duration cooling of the nerve to the extensor digitorum longus muscle of the rat in vivo induced partially reversible denervation of the muscle and atrophy in the type 2 muscle fibers. Increases in cyclic adenosine monophosphate, cyclic guanosine monophosphate phosphodiesterase, adenylate cyclase, and guanylate cyclase were observed in the denervated muscle. Treatment with gangliosides of the bovine brain cortex seemed to improve the excitability of the surviving motor units and to encourage recovery of neuromuscular trophic control, but it did not affect the nerve conduction velocity or the contractile properties of the denervated muscle.
TL;DR: This is the first procedure to have raised the muscle twitch tension in an adult dystrophic mouse to the normal level and overcomes hypoxia in the deeper fibers.
Abstract: Grafting newborn muscle is an innovative method of muscle transplant. This method overcomes hypoxia in the deeper fibers and facilitates reinnervation and revascularization of the grafted muscle fibers, thus promoting the survival and development of the characteristics of the donor muscle. The result achieved is superior to that obtained from mature muscle grafts or from minced muscle transplants. When an intact soleus from a 1-day-old normal mouse was grafted into a recipient soleus of a 20-day-old dystrophic C57BL/6J-dy2J mouse, the actively developing normal graft helped to improve the structure and function of the dystrophic muscle. When compared to the intact dystrophic solei, the test dystrophic muscles five to six months after operation showed increases in cross-sectional area, in wet weight, in twitch and tetanic tension, and in the number of muscle fibers with high resting membrane potentials. This is the first procedure to have raised the muscle twitch tension in an adult dystrophic mouse to the normal level.
TL;DR: Patients in both the allopurinol‐treated group and the placebo group deteriorated at varying rates without evidence of therapeutic benefit, and muscle strength continued to deteriorate during this phase of the study.
Abstract: A double-bline, controlled study was conducted to assess the effects of allopurinol on Duchenne muscular dystrophy. Six patients--three treated with allopurinol and three given a placebo--were followed up for one year and were evaluated by functional and manual muscle testing as well as by determination of serum creatine kinase (CK) levels. Patients in both the allopurinol-treated group and the placebo group deteriorated at varying rates without evidence of therapeutic benefit. To exclude the possibility of error attributable to small sample size, all six patients were treated with allopurinol for an additional eight-week period. Muscle strength continued to deteriorate during this phase of the study.
TL;DR: The voluntary discharge properties and axonal conduction velocity of single motor units were studied in patients with neuromuscular diseases with retained differentiation of the muscle fibers into type 1 and type 2, and in patients in which muscle fibers have only intermediate histochemical properties.
Abstract: The voluntary discharge properties and axonal conduction velocity of single motor units were studied in patients with neuromuscular diseases with retained differentiation of the muscle fibers into type 1 and type 2, and in patients with late-onset hereditary distal myopathy in which muscle fibers have only intermediate histochemical properties. In the patients with muscle fiber differentiation, the findings were similar to those in normal subjects; that is, there was a continuum between motor units which fired tonically at low rates and had a low axonal conduction velocity, and motor units which fired phasically at high rates and had a high axonal conduction velocity. In the patients without muscle fiber differentiation, all motor units had intermediate firing properties and a low axonal conduction velocity. It is suggested that in chronic pathologic states, the differentiation of the muscle fiber histochemistry remains only as long as the differentiation of the motor neurons remains.
TL;DR: The diverse nature of the patients' conditions (cramps and malignancy, and an unusual form of spinocerebellar degeneration) indicate that these abnormal structures are not disease specific.
Abstract: Muscle biopsies from two patients revealed that numerous type 2 fibers contained large abnormal areas filled with cylindrical spirals. The cytochemical profile of these cylindrical spirals was sufficiently characteristic that they could be distinguished from tubular aggregates. Their electron microscopic appearance was unmistakable. Their origin and significance are uncertain. The diverse nature of the patients' conditions (cramps and malignancy, and an unusual form of spinocerebellar degeneration) indicate that these abnormal structures are not disease specific.
TL;DR: The authors' data indicate that there is an impairment in the NADH CoQ region of the respiratory chain of the myodystrophic skeletal muscle mitochondria.
Abstract: A small-scale procedure for preparing tightly coupled intact skeletal muscle mitochondria from myodystrophic (myd/myd) mice is described. Mitochondrial preparations derived from heart, liver, and skeletal muscle of myd/myd and their littermate (+/?) controls are characterized with respect to their cytochrome content and their oxidative and phosphorylative capacities. Our data indicate that there is an impairment in the NADH CoQ region of the respiratory chain of myodystrophic skeletal muscle mitochondria. Both heart and liver mitochondria of myd/myd exhibited normal activities of respiratory chain-linked oxidative phosphorylation.
TL;DR: The consistent clinical and pathologic features of these patients and others described in the literature justify considering this disorder to be a specific nosologic entity.
Abstract: We report four cases of congenital muscular dystrophy; all demonstrated hypotonia and multiple contractures at birth. Strength remained stationary or improved, but the tendency for contracture formation persisted. Brief small amplitude polyphasic potentials were recorded on electromyography, and muscle biopsy revealed extensive fat and/or collagen replacement, which was out of proportion to fiber necrosis or patient strength. The consistent clinical and pathologic features of these patients and others described in the literature justify considering this disorder to be a specific nosologic entity.
TL;DR: It is concluded that both facilitating and inhibiting proprioceptive afferent activity is involved in the differentiation of motor unit firing ranges in sustained isometric voluntary contraction.
Abstract: The firing ranges of 50 normal anterior tibial or short toe extensor motor units in sustained isometric voluntary contraction were studied in electromyographic recordings. The afferent inflow was decreased by compression of the sciatic nerve, thereby blocking large afferents before alpha efferents. Motor units with low minimum and low maximum rates before blockade had higher minimum and maximum rates on blockade. Some motor units with high minimum and maximum rates before blockade had a lower minimum but an unchanged maximum rate on blockade. The firing range recorded for both types of motor unit on blockade was also recorded for all tonically firing motor units during early reinnervation after traumatic lesion to the muscle nerve in 14 patients. It is concluded that both facilitating and inhibiting proprioceptive afferent activity is involved in the differentiation of motor unit firing ranges in sustained isometric voluntary contraction.
TL;DR: It is concluded that incomplete reinnervation of free muscle grafts may be a factor in the failure of such grafts to reattain the mass of control muscles.
Abstract: Free grafts of the extensor digitorum longus (EDL) muscle of the rat are invaded by regenerating nerve fibers during the second postoperative week. Neuromuscular junctions are established during the third week. Levels of choline acetyltransferase (CAT) activity parallel the invasion of the graft by nerve fibers, but this activity never returns to control levels. We conclude that incomplete reinnervation of free muscle grafts may be a factor in the failure of such grafts to reattain the mass of control muscles.
TL;DR: Findings in 11 patients with myopathy varied according to the severity of involvement, butlight weakness of the EFs was associated with an increased twitch:tetanus ratio, decreased tetanic tension, and decreases in the staircase and posttetanic potentiation.
Abstract: Electrical and mechanical responses were evoked in the elbow flexors (EFs) of normal subjects and myopathy patients by maximal stimulation of the musculocutaneous nerve by a wire electrode in the axilla. In normals, the decrement in the mechanical responses during short trains of twitches was small (10%). The potentiation during a staircase decreased with increasing frequency of stimuli, but the potentiation 30 sec after the 100-sec staircase was the same at all frequencies. Posttetanic potentiation was twice as large as the maximal potentiation attained during the staircase. The staircase phenomenon probably results from two opposing events, diminution and potentiation. Findings in 11 patients with myopathy varied according to the severity of involvement. Slight weakness of the EFs was associated with an increased twitch:tetanus ratio, decreased tetanic tension, and decreases in the staircase and posttetanic potentiation. Additionally, severe weakness of the EFs was associated with a diminution in twitch tension.