Myopathic Electromyography Research Articles

Effects of changes in intracellular action potential on potentials recorded by single‐fiber, macro, and belly–tendon electrodes

Some myopathies are accompanied by abnormal calcium homeostasis. Electromyography (EMG) in such patients shows signs of normal or myopathic EMG when detected by a single-fiber electrode and abnormally increased values in macro EMG. As calcium accumulation might be accompanied by changes in intracellular action potential (IAP) and muscle-fiber propagation velocity, we simulated the effects of such changes on motor unit potentials (MUPs) recorded by different kinds of electrodes. We found that: (1) the requirements for what potential can be accepted as a single-fiber action potential (SFAP) are too rigorous; (2) macro MUP amplitude can increase while SFAP amplitude can decrease when there is an increase in the spatial length of IAP spike; and (3) changes in the second phase of a belly-tendon-detected MUP or M wave could be used for noninvasive detection of increased IAP depolarizing (negative) after-potential.

The Electromyographic Features of Acute Rhabdomyolysis

Rhabdomyolysis and acute polymyositis share a similar clinical profile with elevated serum creatine kinase (CK). Unlike polymyositis, the electromyography (EMG) findings of acute rhabdomyolysis with myoglobinuria are not well defined. We retrospectively evaluated 15 patients during the acute phase of rhabdomyolysis. All patients (age range, 10-84 years) underwent electrodiagnostic studies, including needle EMG, during the first 2 weeks from the onset of symptoms. All patients presented with acute myalgia, muscle tenderness, and severe generalized weakness. The median peak CK was 48.0 k u/L (25th and 75th percentiles, 11.0 and 68.0 k u/L), whereas the median CK elevation at the time of EMG examination was 10.0 k u/L (25th and 75th percentiles, 4.5 and 48.5 k u/L). Nerve conduction studies were normal in all except 1 patient who had a preexisting mild polyneuropathy. Needle EMG was performed on 117 muscles. Eighty-seven of 117 (74%) muscles were normal, and 19 of 117 (16%) showed variable proximal myopathic motor unit action potentials. None had persistent fibrillation potentials. One third of patients (5 of 15) had myopathic EMG that was present in 1 to 3 sampled proximal muscles. We conclude that the EMG findings during rhabdomyolysis are often normal and when abnormal, the changes are subtle and are in contrast to the often-prominent EMG findings in polymyositis and dermatomyositis.

Les adjuvants vaccinaux et la myofaciite à macrophages

An unusual inflammatory myopathy characterised by an infiltration of non-epithelioid histiocytic cells has been recorded with increasing frequency in the past 5 years in France. We reassessed some of these cases.We did a retrospective analysis of 18 such cases seen in five myopathology centres between May, 1993, and December, 1997. The myopathological changes were reassessed at a clinopathology seminar.Detailed clinical information was available for 14 patients. The main presumptive diagnoses were polymyositis and polymyalgia rheumatica. Symptoms included myalgias in 12 patients, arthralgias in nine, muscle weakness in six, pronounced asthenia in five, and fever in four. Abnormal laboratory findings were occasionally observed, and included raised creatine kinase concentrations, increased erythrocyte sedimentation rate, and myopathic electromyography. Muscle biopsy showed infiltration of the subcutaneous tissue, epimysium, perimysium, and perifascicular endomysium by sheets of large macrophages, with a finely granular PAS-positive content. Also present were occasional CD8 T cells, and inconspicuous muscle-fibre damage. Epithelioid and giant cells, necrosis, and mitotic figures were not seen. The images were easily distinguishable from sarcoid myopathy and fasciitis-panniculitis syndromes. Whipple's disease, Mycobacterium avium intracellulare infection, and malakoplakia could not be confirmed. Ten patients were treated with various combinations of steroids and antibiotics; symptoms improved in eight patients, and stabilised in two.A new inflammatory muscle disorder of unknown cause, characterised by a distinctive pathological pattern of macrophagic myofasciitis, is emerging in France.

EMG and nerve conduction studies in children with congenital muscular dystrophy

Motor and sensory nerve conduction velocities (NCVs) and needle electromyography (EMG) results were reviewed in 26 children with different types of congenital muscular dystrophy (CMD), including patients with mutations in the genes LAMA2, FKRP, and COL6A2. In every patient, at least one EMG examination detected myopathic changes that were predominant in proximal muscles, although EMG performed at birth was normal in two patients. Brief bursts of high-frequency repetitive discharges were electrically elicited in four patients. Uniformly slowed motor NCVs without signs of denervation were observed in seven patients: five merosin-deficient, one merosin-positive, and one with unavailable merosin status. The merosin-deficient neuropathy also involved sensory nerves in three patients and worsened with age in two. In conclusion, myopathic EMG changes were typical and early findings in all types of CMD. An associated neuropathy was detected in most patients with merosin-deficient CMD, and also in a child with normal merosin expression.

Subclinical skeletal muscle abnormalities in patients with hypertrophic cardiomyopathy and their relation to clinical characteristics

Background: Some mutations of cardiac sarcomeric proteins causing hypertrophic cardiomyopathy (β-myosin heavy chain) are associated with skeletal muscle fiber dysfunction, while subclinical skeletal myopathy can be diagnosed by electromyography (EMG) in a substantial proportion of hypertrophic cardiomyopathy patients. Methods: In 49 consecutive, unrelated patients with hypertrophic cardiomyopathy, conventional EMG of deltoid, vastus lateralis, tibialis anterior and soleus muscles was performed. No patient had clinically detectable muscle weakness. We compared the clinical and echocardiographic characteristics between patients with normal and patients with myopathic EMG. Results: Myopathic EMG findings were demonstrated in 13 patients (26.5%), 26 patients (53.1%) had normal findings and 10 patients (20.4%) had indeterminate recordings. There was no significant difference in mean age, maximum wall thickness, left ventricular fraction shortening, NYHA class, the existence of left ventricular outflow tract obstruction, syncope, or the occurrence of nonsustained ventricular tachycardia in the Holter recording among the three groups. Comparison between the myopathic and the normal group revealed that nine patients from the latter (34.6%) had a positive history of sudden death in the family, whereas no patient had such a history in the former group ( P=0.015). Conclusion: The higher prevalence of a family history of sudden death in patients with normal EMG, although not thoroughly explained by our data, may reflect differences in the genetic substrate produced by the higher prevalence of high-risk mutations that are not expressed in skeletal muscle (e.g. troponin T). Further evaluation in genotyped patients is warranted.

Macrophagic myofasciitis: an emerging entity

An unusual inflammatory myopathy characterised by an infiltration of non-epithelioid histiocytic cells has been recorded with increasing frequency in the past 5 years in France. We reassessed some of these cases. We did a retrospective analysis of 18 such cases seen in five myopathology centres between May, 1993, and December, 1997. The myopathological changes were reassessed at a clinopathology seminar. Detailed clinical information was available for 14 patients. The main presumptive diagnoses were polymyositis and polymyalgia rheumatica. Symptoms included myalgias in 12 patients, arthralgias in nine, muscle weakness in six, pronounced asthenia in five, and fever in four. Abnormal laboratory findings were occasionally observed, and included raised creatine kinase concentrations, increased erythrocyte sedimentation rate, and myopathic electromyography. Muscle biopsy showed infiltration of the subcutaneous tissue, epimysium, perimysium, and perifascicular endomysium by sheets of large macrophages, with a finely granular PAS-positive content. Also present were occasional CD8 T cells, and inconspicuous muscle-fibre damage. Epithelioid and giant cells, necrosis, and mitotic figures were not seen. The images were easily distinguishable from sarcoid myopathy and fasciitis-panniculitis syndromes. Whipple's disease, Mycobacterium avium intracellulare infection, and malakoplakia could not be confirmed. Ten patients were treated with various combinations of steroids and antibiotics; symptoms improved in eight patients, and stabilised in two. A new inflammatory muscle disorder of unknown cause, characterised by a distinctive pathological pattern of macrophagic myofasciitis, is emerging in France.

Enzimas séricas e eletromiografia em doenças Neuromusculares: estudo comparativo de 817 casos

Foram estudadas as enzimas séricas (creatinaquinase, desidrogenase láctica, aldolase, aspartato e alanina aminotransferase) de 817 pacientes e eletromiografias (EMG) de 588 casos de portadores de doenças neuromusculares. As enzimas e as EMG foram relacionadas utilizando testes de estatística descritiva e do qui-quadrado. Foi encontrado aumento importante das enzimas séricas relacionadas com EMG de padrão miopático (mais importante com a creatinaquinase, seguido da aldolase, desidrogenase láctica, aspartato aminotransferase e alanina aminotransferase), e, inversamente, normalidade ou discreto aumento nas EMG normais ou com padrão de desinervação. As EMG com padrões de desinervação não têm qualquer relação com a elevação das enzimas séricas.