Motor unit firing rates and firing rate variability in the detection of neuromuscular disorders.

We have used automatic decomposition electromyography (ADEMG) to study 41 muscles in 29 patients with well-defined peripheral and central motor disorders. In motor neuron diseases motor unit action potentials (MUAPs) showed increased amplitudes, firing rates and firing variability. Relatively large MUAPs sometimes were not identified by the computer program if they lacked sufficient high-frequency signal content, or were too variable in shape. In myopathies the MUAPs showed reduced amplitudes, durations and turns, and sometimes dramatic increases in firing rates. Also, the mean number of MUAPs per recording site was often increased, indicating excessive recruitment. In polymyositis (the best studied myopathy) the nature and magnitude of the MUAP shape and firing abnormalities were usually similar at different levels of contractile force, suggesting that motor units are affected without regard to recruitment order. In upper motor neuron paresis (multiple sclerosis), the shape properties of the MUAPs were normal, but mean firing rates were reduced, and firing variability increased. These findings confirm many of the traditional criteria for distinguishing neurogenic from myopathic disease electrophysiologically at the level of the individual MUAP. In addition, they demonstrate the potential diagnostic sensitivity of MUAP firing rate measurements for detecting neuromuscular dysfunction, and for differentiating between some cases of central and peripheral paresis, but not for distinguishing peripheral neurogenic from myopathic weakness, since firing rates tend to increase in both. Increased firing rate variability may be a marker of central or peripheral neurogenic weakness.

Blink reflex excitability cycle in hemifacial spasm.

We studied electrically elicited blink reflex responses in patients with hemifacial spasm (HFS) by applying single isolated, as well as paired (conditioning and test), stimuli at both sides of the face. Responses after single stimuli were of larger size on the side of the spasm compared with the uninvolved side and controls. With paired stimuli, the inhibitory effect of the conditioning stimuli upon the test stimuli late response (R2), which was always observed in normals, was significantly less pronounced at short interstimuli intervals. This resulted in an enhanced recovery curve of R2, which was observed on the side of the spasm and the contralateral, clinically normal side. Patients with longer disease duration showed more striking abnormalities of the recovery curve. We suggest that there is enhanced excitability of facial motoneurons and of those brainstem interneurons that mediate the blink reflex pathway in patients with HFS.

[Chronic demyelinating polyradiculoneuropathy associated with malignant histiocytosis].

A case of malignant histiocytosis (MH) presenting with peripheral nerve involvement is described. A 67-year-old man initially noted left facial weakness on July 20, 1986. The symptom was improved within a week, however, two weeks later he noticed numbness in his fingers and a burning pain in his legs, which was followed by double vision and progressive weakness in all four limbs. On examination, he was found to have total ophthalmoparesis of the right eye and a trace of the left facial palsy. There was severe weakness of the leg muscles, as well as mild weakness of the arms. This was accompanied by wasting of his limbs. All tendon reflexes were absent. Planter responses were flexor. Although cutaneous sensation was intact, vibratory sense was markedly impaired in the legs below the knees. The sphincter function was mildly disturbed. The sedimentation rate was 32 mm/hr. The hemoglobin was 11.9 g/dl and the leukocyte count was 5,700/mm3. The platelet count fell to 60,000/mm3. Results of routine biochemical and radiological studies were unremarkable. The cerebrospinal fluid protein level was 129 mg/dl with a normal cell count. Motor nerve conduction study revealed marked reduction in amplitude of the compound muscle action potential, slow motor nerve conduction velocities and multifocal conduction blocks along the nerve trunks (the left ulnar nerve in the forearm, the bilateral tibial nerve in the lower leg). F-wave was absent or elicited with prolonged latency and with increased chrono-dispersion. Sensory nerve had normal or nearly normal conduction. EMG sampling showed an impaired interference pattern during voluntary contraction and a few denervation potentials at rest.(ABSTRACT TRUNCATED AT 250 WORDS)

Spastic hypertonia: mechanisms and measurement.

Spastic hypertonia has been defined as a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, as one component of the upper motor neuron syndrome. Heightened muscle tone may be the result of changes intrinsic to the muscle or to altered reflex properties. Increased motoneuronal excitability and/or enhanced stretch-evoked synaptic excitation of motoneurons are mechanisms that might enhance stretch reflexes. Two distinct parameters may be altered in the pathologic stretch reflex--the "set point," or angular threshold of the stretch reflex, and the reflex "gain," or the amount of force required to extend the limb in proportion to the increasing joint angle. Earlier studies fail to dissociate the contributions of reflex threshold and reflex gain. Recent investigations suggest that spastic hypertonia may be the result of a decrease in stretch reflex threshold without significant increase in reflex gain, as was previously believed. Various clinical scales, biomechanical paradigms, pendulum models, and electrophysiologic studies have been used to quantify spastic hypertonia. Biomechanical methods seem to correlate most closely with the clinical state. Spastic hypertonia is but one component of the upper motor neuron syndrome, whose features also include loss of dexterity, weakness, fatigability, and various reflex release phenomena. These other features of the upper motor neuron syndrome may well be more disabling to the patient than changes in muscle tone.

Nerve conduction velocity in man during deep diving to 360 msw.

The function of the sensory and motor median nerves was examined in 6 divers during a simulated dive to 360 meters of seawater (msw), with a mixture of helium and oxygen (heliox) as breathing gas. Divers were examined in the compression chamber before the dive, at 360, 300, 240, 130, 50, and 5 msw, and with skin temperatures ranging from 29.2 degrees to 35.2 degrees C. Examinations were performed with superficial stimulating and recording electrodes. Fast sensory nerve conduction decreased with increase in hyperbaric pressure and with decrease in skin temperature. There was no significant correlation between slow sensory conduction and hyperbaric pressure. Distal motor latency increased with increase in hyperbaric pressure and with decrease in skin temperature. The effect of pressure was independent of temperature. No significant functional changes were detected in the main nerve trunk proximal to the wrist or in the F-wave responses.

Ubiquitin deposits in anterior horn cells in motor neurone disease.

A polyclonal antiserum to ubiquitin, a low molecular weight protein involved in the ATP-dependent removal of abnormal cytoplasmic proteins, has been used to stain spinal cord from 10 cases of motor neurone disease and from 12 control spinal cords. All 10 cases of motor neurone disease exhibited antiubiquitin-immunoreactive deposits in a proportion of the surviving anterior horn cells but these deposits were not seen in any of the 12 controls. These ubiquitin deposits do not correspond to previously described neuronal inclusions in motor neurone disease. The ubiquitin deposits represent, therefore, a new neuronal inclusion which possibly reflects previously unrecognised degradative events occurring in the vulnerable neurones.

Repair of severed peripheral nerve: a superior anatomic and functional recovery with a new "reconnection" technique.

The objective of this study was to use a quantitative functional and anatomic model to compare surgical repair of the rat sciatic nerve according to two techniques; standard epineurial repair and the recently reported "nerve reconnection technique" ("freeze-trim technique"). Functional recovery was evaluated using a functional index based on the measurements of the rats' footprints. Neuroanatomic experiments were conducted on the same animals to correlate functional recovery with regeneration of known motoneuron populations. The results of surgical repairs were also compared to those obtained from untreated sciatic nerve crush injuries. Functional recovery after epineurial repairs typically averaged 18%, whereas the mean recovery from the "nerve reconnection technique" was 71%. Crush injuries recovered to normal and reached a plateau much earlier than the surgical repairs. Retrograde horseradish peroxidase (HRP) labeling of motoneurons of the common peroneal nerve, a branch of the sciatic, revealed that there was a complex relationship between functional recovery and the number and distribution of motoneurons that regenerated axons distal to the repair site. The "nerve reconnection technique" greatly reduced the probability of axonal misdirection into the wrong distal branches at the repair site and brought an improvement of 300% to 400% in functional recovery over that found with epineurial repair. This technique of nerve repair may prove to be a valuable tool in reconstructive surgery.

AAEE minimonograph #31: the electrodiagnosis of ulnar neuropathy at the elbow.

Electrodiagnostic testing is useful in evaluating ulnar nerve elbow lesions. A flexed elbow seems preferable for conduction studies, since it eliminates the elbow segment slowing found in normals done in the extended position. Slowing of the motor velocity in the elbow segment was the most frequent abnormality in this study. Sensory conduction studies and needle examination each provided additional helpful data. Latency to ulnar forearm muscles and "inching" stimulations around the elbow are techniques that also deserve to be included in our standard armamentarium.

Reversible proximal conduction block underlies rapid recovery in Guillain-Barré syndrome.

Three patients with Guillain-Barré syndrome underwent electrophysiological examination prior to and during a period of rapid clinical recovery. In each case, improved strength of the abductor digiti minimi coincided with electrophysiologic evidence of a marked reversal of proximal conduction block. In contrast, the degree of distal conduction block remained relatively unchanged after stimulation at the wrist, elbow, axilla, and Erb's point. These findings indicate that rapid motor recovery, early in the course of Guillain-Barré syndrome, can result from reversal of proximal conduction block and explains the often noted dissociation between clinical improvement and conventional distal nerve conduction studies.

Muscular dystrophy in a litter of golden retriever dogs.

Clinicopathologic findings from two golden retriever dogs with an inherited, progressive, degenerative muscle disease that were studied until 27 and 40 months of age are described. Initial clinical signs included stilted gait and simultaneous advancement of their pelvic limbs. Further gait restriction and muscle hypertrophy eventually occurred. Serum creatine kinase was dramatically elevated (greater than 10,000 U/L). There were persistent "spontaneous" high-frequency discharges (pseudomyotonia) on electromyographic evaluation. Features of both muscle fiber degeneration (hyaline fibers, myophagocytosis) and regeneration (small basophilic fibers) were seen on light microscopy. Similar ultrastructural changes (fiber hypercontraction, increased myoblasts) were present. On morphometric histochemical evaluation, mean fiber diameter of both type 1 and 2 fibers was increased compared with controls in two of three muscles examined. There was no apparent fiber type predominance. Scattered ragged red fibers were seen, but this appeared to be a nonspecific finding of either muscle fiber regeneration or degeneration. These findings and potential contributing pathophysiologic mechanisms are discussed in relation to Duchenne muscular dystrophy.

Nerve conduction studies in upper limbs of patients with cervical spondylosis and motor neurone disease.

Proximal conduction studies by F-wave technique, with conventional distal motor and sensory conduction were performed along the ulnar nerves of 20 patients each with cervical spondylotic radiculopathy and/or myelopathy and with classical motor neurone disease (MND). Such F-wave parameters as shortest F-latency, F-conduction velocity, conduction time and F-ratio were calculated. Twenty-five age- and sex-matched healthy volunteers acted as controls. Proximal slowing associated with sensory conduction abnormalities and normal distal motor conduction favored cervical spondylosis (CS). Distal slowing with a normal proximal motor and sensory conduction was associated with motor neurone disease.

[Double discharges of motor units and tremor strength]. / Doppelentladungen motorischer Einheiten und Tremorstärke.

The relationship between the double-discharges (DDs) of single motor units (MUs) and the tremor strength was studied in 7 patients with parkinsonism and 3 with essential tremor. The potentials of single MUs and the force of the first dorsal interosseus muscle were recorded during slight isometric contractions. The rate of DDs and their interval duration were correlated with the global tremor strength and the amplitudes of the single tremor beats. With increasing tremor strength, the rate of DDs increased and the duration of their intervals decreased. It is concluded that DDs act as tremor amplifiers. This effect is probably accounted for by a more than linear summation of two consecutive MU contractions with short interval which is known from animal experiments.

Suppression of experimental autoimmune neuritis by the oxygen radical scavengers superoxide dismutase and catalase.

Macrophages have been implicated in myelin damage in experimental autoimmune neuritis (EAN). We examined a possible pathogenetic role of toxic oxygen species elaborated by macrophages in EAN by administering oxygen radical scavengers. Early treatment of rats with either catalase or superoxide dismutase (10,000 U/kg/day) protected animals from the development of EAN. Treatment delayed until there was clinical manifestation of EAN (day 13) still markedly attenuated the severity of the disease, as evidenced by clinical assessment, electrophysiological studies, and morphological observation. In cell culture, macrophages from sham-treated controls generated heightened oxidative metabolic responses indicating in vivo macrophage activation. Addition of catalase or superoxide dismutase abrogated or diminished chemiluminescence and production of reactive oxygen intermediates by macrophages ex vivo. Our findings underscore the importance of macrophages in EAN and provide evidence that, in this model, macrophage-derived reactive oxygen intermediates contribute to damage of the myelin sheath.

[Clinical application of the F-wave in various pathological conditions of the peripheral nervous system]. / Applicazione clinica dell'onda F in varie condizioni di patologia del sistema nervoso periferico.

Using the latencies of M response and F-wave, motor nerve conduction was assessed along the entire course of the nerves in various diseases occurring at different levels of the peripheral nervous system. Idiopathic polyneuritis, motor neuron disease, radiculopathies and carpal tunnel syndrome were studied.

Effects of tendon pressure on alpha motoneuron excitability in patients with stroke.

The purpose of this study was to evaluate the effects of two intensities (5 and 10 kg) of continuous and intermittent Achilles tendon pressure on the H-reflex in eight hemiparetic subjects. A decrease in the H-reflex was interpreted as a depression in motoneuron excitability, a condition conducive for reducing muscle tone. The H-reflex measurements were obtained before, during, immediately after, and 2.5 minutes after tendon pressure application. Piecewise linear regression equations were used to evaluate the effects of four pressure conditions. The mean of the midpoints of the lines for each pressure condition was compared with prepressure baseline values by t tests and with the other pressure conditions by an analysis of variance. All four pressure conditions demonstrated H-reflexes less than prepressure baseline values, with three of the four conditions (5 and 10 kg of intermittent pressure and 5 kg of continuous pressure) being significantly less than prepressure baseline values (p less than .05). The analysis of variance revealed a significant difference among pressure conditions. Scheffé post hoc contrast comparisons revealed significant differences between intermittent and continuous pressure but not between 5 and 10 kg of pressure. The results of this study indicate that in these hemiparetic subjects, the H-reflex was depressed during both continuous and intermittent tendon pressure. Intermittent pressure was more effective then continuous, but 10 kg of pressure had no greater effect than 5 kg of pressure. The effects of pressure lasted only as long as the stimulus was present.(ABSTRACT TRUNCATED AT 250 WORDS)