Needle electromyography

Physiologic assessment of diseases of the motor unit from the anterior horn cells to the muscles relies on a combination of needle electromyography (EMG) and nerve conduction studies (NCS). Both require a unique combination of knowledge of peripheral nervous system anatomy, physiology, pathophysiology, diseases, techniques, and electricity is necessary. Successful, high‐quality, reproducible EMG depends on the skills of a clinician in patient interaction during the physical insertion and movement of the needle while recording the electrical signals. These must be combined with the skill of analyzing electric signals recorded from muscle by auditory pattern recognition and semiquantitation. 10 , 52 This monograph reviews the techniques of needle EMG and waveform analysis and describes the types of EMG waveforms recorded during needle EMG. © 2009 Wiley Periodicals, Inc. Muscle Nerve 39: 244–270, 2009     

Le traitement du signal en électromyographie: mise au point

Automatic analysis of electromyography (EMG) signals, first operated in 1950 with analogic machines, steeply expanded from 1980 when fast computers and worthwhile programs became available. On-line measurement of response area and latency, averaging of low amplitude waves, fast sorting of motor unit potential shape parameters, computation of the “jitter” between two muscle fibers, turns/amplitude and spectral analysis of interferential pattern records, are some examples of programs currently offered in modern EMG machines. Other techniques are still reserved for research purposes: scanning EMG, decomposition of nerve and muscle compound potentials, measurement of the threshold and firing rate of motor units, trace analysis using tracking models. Finally, the credit for artificial intelligence systems (knowledge based systems, fuzzy logic, neuronal networks) is still not clearly stated.     

近端/远端复合肌肉动作电位振幅比率在术后面神经功能评估上的价值

目的 探讨近端/远端复合肌肉动作电位振幅比率在术后面神经肿瘤侵犯段功能评估上的价值和对早期面神经修复的指导意义。方法 比较术末面神经近端/远端复合肌肉动作电位振幅比率和术后2周、6个月患侧面神经功能的H-B分级之间的关系。结果 术后6个月面神经H-B分级恢复到Ⅰ-Ⅱ级者,术末近端/远端复合肌肉动作电位振幅比率均>0.3。结论 术末面神经近端/远端复合肌肉动作电位振幅比率是判断术后面神经远期功能,特别是肿瘤侵犯段功能的重要指标,为术中直接修复面神经提供了指导依据。     

Neurogenic muscle hypertrophy in radiculopathy

The course of radiculopathy is sometimes associated with weakness and wasting of muscles. Very rarely in such cases, however, is hypertrophy of muscle fibres observed. Three cases are presented of sciatica with enlarged calves caused by hypertrophy of type 1 or types 1 and 2 muscle fibres. In light of the literature and the results obtained, an attempt is made to explain the cause of rare clinical symptoms and draw attention to diagnostic and therapeutic difficulties.     

Proximal myotonic myopathy

Three Swedish patients with proximal muscle weakness, myotonia and lack of CTG expansion on genetical analysis are presented. Clinical neurological and neurophysiological examination and muscle biopsy were performed. There was an indication of autosomal dominant inheritance in 2 of the 3 patients. The main symptoms and clinical findings in the 3 patients were weakness of the proximal muscles, myotonia, muscle stiffness, muscle pain and muscle atrophy. Neurophysiological examination showed myotonic bursts and muscle biopsy snowed a variation of fibre sizes, an increased number of muscle fibres with centralized nuclei and scattered atrophic muscle fibres. Laboratory data showed elevated CK, GT and LD in 1 patient. Before genetical analysis was performed, all 3 patients had been diagnosed as atypical cases of myotonic dystrophy. However, the symptoms, clinical signs, laboratory data, electrophysiological and muscle biopsy findings were compatible with proximal myotonic myopathy (PROMM).     

Motor unit potential contribution to surface electromyography

The background of the bioelectric activity of muscle recorded from the surface of the skin (surface electromyography) in terms of the representation of single motor units of the underlying muscle(s) is not very well documented or understood. An insight into the composition of an electromyogram is essential for the proper interpretation of one of the most widely applied electrophysiological techniques. In the present paper, a study of the contribution of single motor unit potentials to the surface electromyogram is presented. To this end, the decline of different components of the motor unit potential with depth of the motor unit is quantified. Experimentally, the action potentials from motor units at several positions in the muscle were recorded by 30 skin surface electrodes. Simultaneous use of scanning electromyography provided information about the actual position and size of the motor unit. Observed linear log–log relationships between motor unit potential magnitudes and distance indicated the usefulness of a power function to describe the motor unit potential's dependence on recording distance. It is shown that different specific surface motor unit potential characteristics fall off differently with depth. The magnitude–distance relationship is shown to be dependent on the recording configuration (unipolar vs. bipolar recording, including the inter-electrode distance) and the chosen motor unit potential parameter (negative peak amplitude, positive peak amplitude and area).     

EMG myokymia as a cause of ptosis in hypothyroidism

Ptosis is known to be associated with thyroid disorders. We describe two biochemically corrected hypothyroid patients presenting with isolated bilateral ptosis. EMG of the orbicularis oculi showed continuous grouped motor unit potentials. In the absence of obvious aetiology, it is hypothesised that focal demyelination of terminal branches to the orbicularis oculi may play a role in the generation of the discharges.     

Movement disorders in patients with peripheral facial palsy.

Acute unilateral facial paralysis is usually a benign neurological condition that resolves in a few weeks. However, it can also be the source of a transient or long-lasting severe motor dysfunction, featuring disorders of automatic and voluntary movement. This review is organized according to the two most easily recognizable phases in the evolution of facial paralysis: (1). Just after presentation of facial palsy, patients may exhibit an increase in their spontaneous blinking rate as well as a sustained low-level contraction of the muscles of the nonparalyzed side, occasionally leading to blepharospasm-like muscle activity. This finding may be due to an increase in the excitability of facial motoneurons and brainstem interneurons mediating trigeminofacial reflexes. (2). If axonal damage has occurred, axonal regeneration beginning at approximately 3 months after the lesion leads inevitably to clinically evident or subclinical hyperactivity of the previously paralyzed hemifacial muscles. The full-blown postparalytic facial syndrome consists of synkinesis, myokymia, and unwanted hemifacial mass contractions accompanying normal facial movements. The syndrome has probably multiple pathophysiological mechanisms, including abnormal axonal branching after aberrant axonal regeneration and enhanced facial motoneuronal excitability. Although the syndrome is relieved with local injections of botulinum toxin, fear of such uncomfortable contractions may lead the patients to avoid certain facial movements, with the implications that this behavior might have on their emotional expressions.     

Complete bilateral internal ophthalmoplegia as sole clinical sign of botulism: confirmation of diagnosis by single fibre electromyography

Summary A case of complete bilateral internal ophthalmoplegia as the sole clinical sign of botulism is reported. Diagnosis was immediately confirmed by single-fibre electromyography (SFEMG), which revealed abnormally high blocking (14.3%), contrasting with moderately increased jitter (mean consecutive difference in the extensor digitorum communis muscle, 43.9 s). After giving equine botulinum antitoxin and simultaneous forced emptying of the bowels, ocular symptoms completely disappeared within 2 days. Six days, 5 weeks and 6 months after the first SFEMG study, the jitter was still abnormal, even becoming more so with time. Blocking, however, was only rarely observed in the follow-up studies. It is concluded that SFEMG may serve as a useful and sensitive method for the rapid diagnosis of botulinum intoxication, even in cases where no clinical signs of general muscular weakness are apparent.This paper was presented in part at the Congress of the International Medical Society of Motor Disturbances (ISMD), Rome, Italy, 2–4 June 1988     

Reversal of profound paralysis: use of large doses of edrophonium to antagonize vecuronium and pancuronium induced neuromuscular blockade

The ability to evoke reversal of dense vecuronium- and pancuronium-induced paralysis (T1 10% of control) with edrophonium 1.0 mg.kg-1 was studied using train-of-four nerve stimulation and electromyographic monitoring. Two different end-points, train-of-four ratios of 0.5 and 0.7, were used to define "adequate reversal", and the results for both relaxants were compared. Reversal was reliable and rapid for vecuronium if either ratio was used with times of 2.8 (1.5) and 9 (3) min required to achieve ratios of 0.5 and 0.7, respectively. However, if the block was due to pancuronium, reversal was unreliable with 2 of 9 and 4 of 9 patients not achieving ratios of 0.5 and 0.7, respectively. Reversal was also markedly prolonged in this group with a mean time of 37 (23) min to achieve a ratio of 0.7, and in almost half these patients a supplementary dose of edrophonium was required.