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Neuromuscular Junction Syndromes and Ocular Myopathies
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Due to variation in site of action, repetitive nerve stimulation test also gives varied results. While decremental response at low frequency stimulation is suggestive of a postsynaptic neuromuscular blockade, low amplitude action potentials, decremental response on high frequency stimulation is representative of presynaptic neuromuscular blockade. Fibrillations may also be seen on electromyography.
Myasthenia Gravis
Published in K. Gupta, P. Carmichael, A. Zumla, 100 Short Cases for the MRCP, 2020
K. Gupta, P. Carmichael, A. Zumla
. Confirmatory investigations include: Repetitive nerve stimulation.Anti-acetylcholine receptor antibodies (anti-AChR).
Hematopoietic Stem Cell Therapy for Patients with Refractory Myasthenia Gravis
Published in Richard K. Burt, Alberto M. Marmont, Stem Cell Therapy for Autoimmune Disease, 2019
The diagnosis of MG is made by clinical manifestations, improvement to the anticholinesterase edrophonium chloride (Tensilon), and EMG. MG is characterized by weakness, often fluctuating, being worsened by exercise. Fatigue and weakness may occur in ocular, facial, bulbar, and/or limb muscles.9,10 Ocular ptosis, ophthalmoparesis, dysarthria, and dysphagia are common. In severe cases, respiratory muscles are affected. Electrophysiologic studies reveal loss of amplitude with repetitive nerve stimulation. Approximately 85% of patients with MG have anti-AChR antibodies. These patients may have other genetic or autoimmune-mediated problems with the nerve-muscle synapse. Achieving action potential threshold depends on clustering of the AChR at the motor endplate. A neuronal protein, agrin, activates muscle-specific kinase (MuSK) to cluster AChRs via rapsyn, a muscle cytoplasmic synapse protein (Fig. 1).24-26 Some MG patients without anti-AchR antibodies have antibodies to MuSK. Therefore, disruption of AChR clustering by either antibodies to AChR or MuSK results in the same clinical manifestations and EMG findings. MG must also be differentiated from other myasthenic syndromes such as Eaton Lambert syndrome, which is a malignancy-associated disorder with antibodies against PQ-type voltage-gated calcium channels.27 Eaton Lambert syndrome can be distinguished from MG by EMG.
Electrophysiologic evaluation of myasthenia gravis and its mimics: real-world experience with single-fiber electromyography
Published in Hospital Practice, 2022
Anthony Khoo, Hnin Hay Mar, Maria Victoria Borghi, Santiago Catania
The outcome of SFEMG was recorded, as were details of muscles tested, total pairs obtained, number of abnormal pairs, degree of jitter and presence of blocking. Results of RNS were noted including which muscles were examined and the timing of any significant decrement. Repetitive nerve stimulation of the median and ulnar nerve at the wrist were considered distal sites, whereas RNS of facial and spinal accessory nerves were considered proximal sites. At each site, RNS involved a train of 10 pulses at 3 Hz, and was performed before and at one-minute intervals after one minute of muscle contraction. Standard operating procedure at our center mandates skin temperature recordings >32 degree Celsius although this was not systematically recorded in most studies. Repetitive nerve stimulation was considered abnormal if there was a decrement of >10% in comparing the baseline compound motor action potential (CMAP) amplitude or area with the 4th or 5th CMAP recorded. For every patient, we recorded whether pyridostigmine had been taken and the timing of the last dose. Where performed, findings of routine nerve conduction studies and electromyography of proximal muscles were also recorded.
Scrub Typhus Presenting as Unilateral Abducens Nerve Palsy
Published in Neuro-Ophthalmology, 2022
Ritwik Ghosh, Subhrajyoti Biswas, Arnab Mandal, Kaustav De, Srijit Bandyopadhyay, Sona Singh Sardar, Arpan Mandal, Julian Benito-León
Routine blood tests were normal, except for raised erythrocyte sedimentation rate (56 mm/hr) and mild elevations of transaminases without hyperbilirubinaemia. Anti-nuclear antibody (ANA) screening using HEp-2 cells, ANA profile, antiphospholipid antibodies, anti-neutrophil cytoplasmic antibodies (cANCA and pANCA) were negative. Anti-acetylcholine receptor and anti-muscle-specific tyrosine kinase antibodies as well as anti-thyroid peroxidase and anti-thyroglobulin antibodies were also negative. Electrophysiological testing, including repetitive nerve stimulation and single fibre electromyography, was normal. Brain magnetic resonance imaging (MRI) with gadolinium revealed mild thickening and enhancement along the lateral walls of both cavernous sinuses (left more than right), basal cistern and posterior inter-hemispheric fissure, suggestive of meningitis (Figure 1). Cerebrospinal fluid (CSF) analysis revealed a mononuclear pleocytosis (20 cells/µl, all lymphocytes), normal glucose (45 mg/dL), and elevated protein content (102 mg/dL). Other CSF studies, including cytology examination, and cultures for relevant bacteria were negative, except for the presence of IgM antibodies against Orientia tsutsugamushi in both serum and CSF. Subsequently, a polymerase chain reaction confirmed the presence of Orientia tsutsugamushi in the CSF.
Paraneoplastic Ophthalmoplegia as the Presenting Sign of Paediatric Glioblastoma Multiforme: A Case Report
Published in Neuro-Ophthalmology, 2021
Arjan S. Dhoot, Caroline Just, Lulu LCD Bursztyn
Initial magnetic resonance imaging (MRI) showed two small poorly defined non-enhancing areas of T2 and fluid-attenuated inversion recovery (FLAIR) hyperintensity and possible increased bulk in the posterior right medial frontal lobe (Figure 2), consistent with infection, inflammation, or a low-grade neoplasm. It was felt that these changes were not related to his ophthalmoplegia and thus no biopsy was pursued. Lumbar puncture and full body computed tomography were unremarkable. Negative laboratory investigations included thyroid peroxidase antibodies, thyroid stimulating hormone, free-T3, free-T4, neuromyelitis optica antibodies, anti-neutrophilic cytoplasmic autoantibodies, acetylcholine receptor antibodies (ARAB), muscle-specific kinase (MuSK) antibodies, cryoglobulins, anti-GQ1b, C-reactive protein, anti-phospholipid antibodies, Borrelia serology, anti-glutamic acid decarboxylase (GAD) antibodies, anti-N-methyl D-aspartate receptor (NMDA-R) antibodies, and a paraneoplastic panel (including anti-Hu, anti-Yo, anti-Ri, anti-amphiphysin, and anti-MA). Anti-GAD, anti-NMDA-R, and the paraneoplastic panel were also tested in the cerebrospinal fluid and were negative. Electromyography and nerve conduction studies were performed, including repetitive nerve stimulation, and showed no decrement or increment and normal velocities and amplitudes. Abnormal bloodwork included a mildly elevated erythrocyte sedimentation rate of 18 mm/hr, respiratory syncytial virus, and anti-RO autoantibodies.