Low-amplitude Compound Muscle Action Research Articles

Defective E2 electrode lead gives low-amplitude compound muscle action potential.

Low-amplitude compound muscle action potential (CMAP) suggests a neuromuscular pathology. Low amplitude will also result from a defective E1 electrode or its lead, that is, a technical artifact. The aim of this study was to investigate the effect of a defective E2 electrode lead on the CMAP. The CMAP was recorded using standard nerve conduction methodology and all electrode leads connected properly. Signals were then recorded when either the E1 or the E2 electrode lead was disconnected from the amplifier. This simulated a defective electrode lead. Studies were performed in four nerves of a healthy subject. CMAP amplitude was reduced as expected when E1 was disconnected. Surprisingly, the amplitude fell by more than 65% when the E2 lead was disconnected, although E1 was properly connected. E1 and E2 electrodes contribute to the CMAP. A defective recording electrode lead to E1 or E2 results in a low-amplitude CMAP. The amplitude drop observed with a disconnected E2 lead was far greater than the signal recorded by the E2 electrode. This occurs due to the amplifier's inherent property to reduce the voltage difference between the E1 and E2 inputs. When E2 lead is defective, the CMAP will be an attenuated version of the signal recorded by the E1 electrode, and vice versa. When low-amplitude CMAP amplitude is observed in all conduction studies, technical artifact should be considered before exploring the pathological basis for the abnormal results.

A DISTINCT KIND OF MORNING SICKNESS: WOUND BOTULISM IN A PREGNANT FEMALE

SESSION TITLE: Wednesday Medical Student/Resident Case Report Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM INTRODUCTION: Wound botulism is caused by contamination with Clostridium Botulinum spores. When the spores germinate, they produce a potent neurotoxin causing the characteristic descending flaccid paralysis. Botulism in pregnancy may be amplified due to natural physiological changes. To the best of our knowledge, there have been only two other cases reported of pregnant women with wound botulism. CASE PRESENTATION: This is a 38-year-old female with hypertension, asthma, and 10-week intrauterine pregnancy who presented with two weeks of diplopia, dysphasia, dysarthria, anorexia, and ptosis followed by symmetric and progressive weakness in her legs. Physical exam revealed diminished patellar reflexes, weakness of bilateral lower extremities, and swollen and bruised forearms, without ultrasound evidence of fluid collection. Due to decreased vital capacity, she was intubated for airway protection. Initial serological and spinal fluid studies were normal. Brain and spine imaging were unremarkable. Electromyography (EMG) revealed gross reduction in motor response amplitudes suggestive of an axon loss variant of Guillan Barre syndrome. IVIG therapy was initiated. Due to progressive weakness and persistent ventilator support, the patient underwent tracheostomy. Further history provided by significant other confirmed IV drug use 2 weeks prior broadening the differential diagnosis. Acetylcholine receptor binding antibody was negative, yet botulism neurotoxin was positive and the heptavalent antitoxin was administered. Repeat EMG demonstrated progressive low amplitude compound muscle action potentials with minimal increment and early recruitment on rapid repetitive stimulation suggested the presence of a presynaptic neuromuscular junction defect consistent with botulism. The patient’s clinical status dramatically improved. Although her fetus was unharmed, she decided to terminate her pregnancy due to psychosocial issues. DISCUSSION: Unlike foodborne botulism, wound contamination requires spore germination before the toxin can be released resulting in longer incubation periods. The neurotoxin inhibits the release of acetylcholine from the motor neurons to the muscles. The blockade is most pronounced in the cranial nerves and muscles of respiration, sparing sensory innervation. Treatment must be initiated with a presumptive clinical diagnosis, as laboratory confirmation is timely. Prognosis is favorable with proper respiratory support and early recognition. There is minimal literature describing maternal and fetal outcomes, however congenital botulism or neonatal loss is deemed unlikely. CONCLUSIONS: Early recognition and neutralization of the neurotoxin is paramount to improve outcomes. Pregnant women physiologically have increased oxygen consumption causing rapid progression of respiratory failure. There are no known adverse maternal or fetal outcomes from treatment or infection of botulinum toxin. Reference #1: Burningham, Mark D, et al. “Wound Botulism.” Anals of Emergency Medicine 1994 Dec;24(6):1184-1187. Reference #2: Thwaites, C.L. "Botulism and tetanus.” Medicine 2017 Dec;45(12):739-742. Reference #3: Rimawi, Bassam H. "Botulism During Pregnancy and the Postpartum Period: A Systematic Review.” Clinical Infectious Disease 2018 Jan;66(Suppl 1):S30-S37. DISCLOSURES: No relevant relationships by Aarti Mittal, source=Web Response No relevant relationships by Erin Wiltchik, source=Web Response

Preoperative Evaluation of Iatrogenic Spinal Accessory Nerve Palsy: What Is the Place for Electrophysiological Testing?

Electrophysiological testing has been used for the early diagnosis of iatrogenic spinal accessory nerve palsy in clinical practice. However, the presence of low-amplitude compound action potential in 70% to 90% of the patients suffering from iatrogenic nerve transection was reported in several studies. We have encountered the same issue and made minor modifications to the methods of electrophysiological testing. The purpose of this study was to retrospectively evaluate the reliability of our modified electrophysiological testing as preoperative examination in patients receiving surgical revision. In this study, we compared preoperative electrophysiological testing results with intraoperative diagnosis in the 24 patients with iatrogenic spinal accessory nerve palsy who were referred to our hospital from 2009 to 2018. During operation, 20 patients were diagnosed with neurotmesis and the remaining 4 patients were found axonotmesis depending on the results of surgical exploration and intraoperative electrophysiological examination. Six of the 20 patients with neurotmesis demonstrated a low-amplitude compound muscle action potential of the upper trapezius during preoperative electrophysiological testing. Needle electromyography revealed voluntary motor unit potentials in 8 of the 20 patients. Meanwhile, concomitant great auricular nerve or dorsal scapular nerve injuries were preoperatively revealed in 7 of 24 patients. The rate of low-amplitude compound muscle action potentials in these patients suffering from spinal accessory nerve neurotmesis was about 30% with our modified electrophysiological testing. We should be aware of this pitfall before surgical nerve repair. Furthermore, electrophysiological testing is an informative preoperative examination revealing the concomitant nerve injuries.

Lambert-Eaton Syndrome in Children

Investigators from Boston Children's Hospital; the Lahey Clinic, Burlington, MA; and Ohio State University, report 3 children presenting between ages 9 and 10 years with proximal lower extremity weakness with areflexia and low-amplitude compound muscle action potentials, and diagnosed with Lambert-Eaton myasthenic syndrome.

Electrophysiology of neuromuscular disorders in critical illness

Neuromuscular disorders, predominantly critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) occur in approximately one-third of patients in intensive care units. The aim of this study was to review the important role of electrophysiology in this setting. In CIM, sarcolemmal inexcitability causes low amplitude compound muscle action potentials (CMAPs) that may have prolonged durations. Needle electrode examination usually reveals early recruitment of short duration motor unit potentials, often with fibrillation potentials. In CIP, the findings are usually those of a generalized axonal sensorimotor polyneuropathy. Direct muscle stimulation aids in differentiating CIP and CIM and in identifying mixed disorders along with other electrodiagnostic and histopathologic studies. Identifying evolving reductions in fibular CMAP amplitudes in intensive care unit (ICU) patients predicts development of neuromuscular weakness. Knowledge of the various neuromuscular disorders in critically ill patients, their risk factors, and associated electrodiagnostic findings can lead to development of a rational approach to diagnosis of the cause of neuromuscular weakness in ICU patients.

Acute motor axonal neuropathy during intensive immunosuppressive therapy for macrophage activation syndrome

We describe a 2-year-old girl with refractory macrophage activation syndrome (MAS), which is a serious complication of inflammatory disorders associated with rheumatic disease in children. Although she was treated with intensive immunosuppressive therapies such as immunoglobulin, plasma exchange, dexamethasone, methotrexate, cyclosporine, and etoposide, she subsequently developed motor deficit with the abolition of deep tendon reflexes. Since nerve conduction study revealed low-amplitude compound muscle action potentials and motor conduction slowing, she was diagnosed as having acute motor axonal neuropathy (AMAN) associated with refractory MAS. This is the first report of AMAN occurring during immunosuppressive therapy for extremely refractory MAS, suggesting that hypercytokinemia or activated macrophages may have played a critical role in the pathogenesis of AMAN in this patient.

An Outbreak of Botulism in Thailand: Clinical Manifestations and Management of Severe Respiratory Failure

Northern Thailand's biggest botulism outbreak to date occurred on 14 March 2006 and affected 209 people. Of these, 42 developed respiratory failure, and 25 of those who developed respiratory failure were referred to 9 high facility hospitals for treatment of severe respiratory failure and autonomic nervous system involvement. Among these patients, we aimed to assess the relationship between the rate of ventilator dependence and the occurrence of treatment by day 4 versus day 6 after exposure to bamboo shoots (the source of the botulism outbreak), as well as the relationship between ventilator dependence and negative inspiratory pressure. We reviewed the circumstances and timing of symptoms following exposure. Mobile teams treated patients with botulinum antitoxin on day 4 or day 6 after exposure in Nan Hospital (Nan, Thailand). Eighteen patients (in 7 high facility hospitals) with severe respiratory failure received a low- and high-rate repetitive nerve stimulation test, and negative inspiratory pressure was measured. Within 1-65 h after exposure, 18 of the patients with severe respiratory failure had become ill. The typical clinical sequence was abdominal pain, nausea and/or vomiting, diarrhea, dysphagia and/or dysarthria, ptosis, diplopia, generalized weakness, urinary retention, and respiratory failure. Most patients exhibited fluctuating pulse and blood pressure. Repetitive nerve stimulation test showed no response in the most severe stage. In the moderately severe stage, there was a low-amplitude compound muscle action potential with a low-rate incremented/high-rate decremented response. In the early recovery phase, there was a low-amplitude compound muscle action potential with low- and high-rate incremented response. In the ventilator-weaning stage, there was a normal-amplitude compound muscle action potential. Negative inspiratory pressure variation among 14 patients undergoing weaning from mechanical ventilation was observed. Kaplan-Meier survival analysis identified a shorter period of ventilator dependency among patients receiving botulinum antitoxin on day 4 (P=.02). Patients receiving botulinum antitoxin on day 4 had decreased ventilator dependency. In addition, for patients with foodborne botulism, an effective referral system and team of specialists are needed.

Lambert—Eaton myasthenic syndrome (LEMS) in association with lymphoproliferative disorders

LEMS is a presynaptic neuromuscular junction disorder typically associated with small cell lung carcinoma. The characteristic electrophysiological abnormality is a low amplitude compound muscle action potential that shows a marked increment after short maximal contraction or brief tetanic nerve stimulation. Here we describe 3 patients who had LEMS in association with lymphoproliferative disorder. The first patient had Castleman's syndrome with typical clinical and electrophysiological features of LEMS, which responded partially to treatment with 3-4-diaminopyridine. The second patient was a 7-year-old boy who had an unusual acute onset of LEMS associated with relapse of his Burkitt's leukemia. The third patient was a 60-year-old woman with non-Hodgkin's lymphoma. These 3 patients (together with 6 additional patients identified in the literature) lead us to suggest that lymphoproliferative diseases are another, hitherto unrecognized, type of malignancy associated with LEMS. Thus, any patient with these malignancies and unexplained muscle weakness should have electrophysiological evaluation for LEMS.

There are no neurophysiologic features characteristic of “axonal” Guillain–Barré syndrome

Classical views hold Guillain-Barré syndrome (GBS) as a primary inflammatory-demyelinating neuropathy in which secondary axonal degeneration may occur, particularly when inflammatory lesions are severe. Feasby and colleagues proposed that primary axonal degeneration can also cause GBS characterized by inexcitable motor nerves and poor outcome. This hypothesis rests largely on the results of a single autopsy in which no inflammation or demyelination were found. Using an illustrative case report confirming earlier studies, we point out that inexcitable motor nerves (or low amplitude compound muscle action potentials [CMAPs]) are of ambiguous significance and may reflect distal demyelination, causing conduction block between distal stimulation sites and target muscles, a pattern not uncommon in GBS. Recovery from such lesions may occur within weeks with restoration of CMAP amplitudes. The recognition of a yet unproven axonal variant of GBS cannot be based solely on documentation of inexcitable motor nerves in the context of rapidly developing weakness.