Electrophysiologic evaluation of myasthenia gravis and its mimics: real-world experience with single-fiber electromyography.

OBJECTIVES: In centers which routinely perform single fiber electromyography (SFEMG) for suspected myasthenia gravis (MG), the additional benefit of other neurophysiologic investigations and the frequency of myasthenia mimics has not been ascertained. We aimed to illustrate the range of neurological and non-neurological myasthenia mimics referred for evaluation, and contrast features of their electrophysiologic evaluation with confirmed MG. METHODS: We reviewed all SFEMG studies performed at our center between 1 January 2018 and 31 December 2020. Patient demographics, clinical phenotype, antibody status and final diagnosis were recorded. Electrophysiologic findings were correlated with clinical features and sensitivity analyses performed. RESULTS: A total of 528 SFEMG studies were performed, of which 213 (41%) were abnormal. A diagnosis of MG was made in 101 individuals, including 46 with ocular MG and 35 with seronegative disease. Compared to myasthenia mimics with an abnormal SFEMG, individuals with MG had higher median jitter (mean consecutive difference 61 µs vs. 42 µs, p < 0.001) and a greater percentage of abnormal pairs (61% vs. 33%, p < 0.001) on SFEMG. Repetitive nerve stimulation was abnormal in 27.1% of people with MG and was associated with a generalized clinical phenotype (OR 4.17; 95% CI 1.67-10.48). Thirteen (2%) individuals with MG had normal SFEMG, of whom 10 were in clinical remission. Functional neurological disorders, cranial nerve palsies, primary ocular disease and myopathy were frequent myasthenia mimics. CONCLUSION: SFEMG can be abnormal in a number of myasthenia mimics, and routine nerve conduction studies and electromyography should always be undertaken. In centers where SFEMG is performed routinely for the investigation of suspected MG, extensive proximal repetitive nerve stimulation can be foregone without substantially affecting diagnostic evaluation. Normal SFEMG in those with confirmed myasthenia gravis may help indicate clinical remission.

Sleep deprivation and melatonin for inducing sleep in paediatric electroencephalography: a prospective multicentre service evaluation.

AIM: To compare the efficacy of the main methodologies in attaining sleep and electroencephalography (EEG) abnormalities in children with a view to producing recommendations on best practice. METHOD: Fifty-one UK centres participated. Methods for sleep induction (sleep deprivation, melatonin, and combined sleep deprivation/melatonin) were compared. Data pertaining to demographics, achievement of stage II sleep, and recording characteristics (duration of study, presence of epileptiform activity in awake/sleep states) were prospectively collected for consecutive patients in November and December 2013. RESULTS: Five hundred and sixty-five patients were included. Age range was 1 years to 17 years (mean 7y 10mo), 27.7 per cent had an underlying neurobehavioural condition. Stage II sleep was achieved in 69 per cent of sleep deprived studies, 77 per cent of melatonin studies, and 90 per cent of combined intervention studies (p<0.001, χ2 ). In children who slept, there was no difference between the three interventions in eliciting epileptiform discharges. In children who did not sleep, epileptiform abnormalities were seen more often than after sleep deprivation alone (p=0.02, χ2 ). Seizures were rare. INTERPRETATION: Combined sleep deprivation/melatonin is more effective than either method alone in achieving sleep. The occurrence of epileptiform activity during sleep is broadly similar across the three groups. We recommend the combined intervention to induce sleep for paediatric EEG. WHAT THIS PAPER ADDS: Combined sleep deprivation/melatonin is more effective in achieving sleep than either sleep deprivation or melatonin alone. Sleep latency is shorter with combined sleep deprivation/melatonin. When children do sleep, there is no difference in the occurrence of epileptiform abnormalities between different induction methods. Seizures are rare in sleep electroencephalography recordings.

Reversible spontaneous EMG activity during myasthenic crisis: Two case reports.

BACKGROUND: Myasthenia Gravis (MG) is an antibody-mediated autoimmune neuromuscular disorder, clinically presenting with fatigable variable muscle weakness. Typical electrodiagnostic findings are a decremental response to repetitive nerve stimulation with post-exercise facilitation, and motor unit instability expressed as increased jitter on single fibre-EMG. Presence of spontaneous activity on standard EMG is traditionally considered inconsistent with a diagnosis of MG and would direct the differential diagnosis towards a primary denervating or usually inflammatory myopathic process.Case reportWe herein present two patients with progressive severe bulbar symptomatology, whose needle-EMG examinations showed spontaneous activity and led to erroneous initial diagnoses of inflammatory myopathy and anterior horn cell disease respectively. Follow-up neurophysiological investigations, positive anti-AchR titres and good response to IVIg and steroids eventually established the diagnosis of Myasthenia Gravis. CONCLUSIONS: Clinically severe Myasthenia Gravis can potentially present with spontaneous activity on EMG, mimicking acute myopathic or neurogenic processes. This can prove particularly perplexing and cause significant delays in the diagnosis and treatment of a myasthenia relapse.

How Do I Evaluate and Inject for Writer's Cramp?

Writer's cramp is a disabling focal dystonia, often accompanied by tremor, for which botulinum toxin injections are now the therapy of choice. However, the success of this treatment relies on the correct clinical selection of muscles responsible for the dystonic movements and the subsequent accurate administration of botulinum toxin into what are often very small and difficult to palpate muscles. In order to obtain the best possible outcomes, and to minimize side effects, it is necessary to use guidance from ultrasound or electromyography (EMG). In this video, we will explain how we evaluate patients with writer's cramp and demonstrate how we treat them with EMG guidance.

Effect of botulinum toxin treatment on quality of life in patients with isolated lingual dystonia and oromandibular dystonia affecting the tongue.

The purpose of this study was to investigate the impact of botulinum toxin (BoNT) treatment on the quality of life (QoL) for patients with prominent lingual dystonia (LD) using a disease-specific questionnaire, the oromandibular dystonia questionnaire-25 (OMDQ-25). This is a prospective, observational study of a cohort of 30 patients treated with BoNT injections for LD, with or without concurrent jaw dystonia. Primary efficacy outcome was the absolute difference between total OMDQ-25 baseline score and total OMDQ-25 scores 4 and 8 weeks after the treatment. Safety outcome was the occurrence of adverse effects. The mean total OMDQ-25 baseline score was 46.8 ± 17.8. After BoNT treatment, there was a significant reduction in the mean total OMDQ-25 score at 4 weeks (38.2 ± 17.6; p = 0.004), as well as at 8 weeks (39.6 ± 18.1; p = 0.008). At the multiple regression analysis, a jaw deviation pattern (JDD) and high questionnaire baseline total score were detected as predictors of a better outcome, whilst associated jaw tremor was a predictor of poor outcome. In patients with JDD, jaw-opening muscles were more frequently injected and genioglossus less frequently than in patients without JDD. No major adverse events were detected. A consistent and measurable improvement in QoL, with good safety and tolerability, can be achieved in patients with prominent LD by injecting BoNT into genioglossus and/or other muscles of the oromandibular region.

Secondary nonresponsiveness to botulinum toxin A in cervical dystonia: the role of electromyogram-guided injections, botulinum toxin A antibody assay, and the extensor digitorum brevis test.

We studied 20 patients with cervical dystonia who had started to respond poorly to botulinum toxin A (BTXA) injections after an initial good response. All patients had extensor digitorum brevis (EDB) tests performed in addition to BTXA immunoprecipition assay (IPA) and mouse bioassay (MBA) antibody testing. The patients were reexamined and then treated with carefully placed electromyogram (EMG)-guided BTXA. Nine patients had a good clinical response to EMG-guided injections and all of these patients showed an obvious decrement on the EDB test. All were BTXA blocking antibodies (Abs)-negative via IPA and MBA (apart from one patient who had low BTXA antibodies titers using IPA but no antibodies by MBA). In the other 11 patients, there was a poor clinical response to EMG-guided BTXA injections. Seven of these 11 had small EDB decrement and BTXA antibodies using IPA, suggesting resistance to BTXA. Of the remaining four patients, two had obvious EDB decrement and low antibody titers via IPA (one of them had no antibodies via MBA), while the other two patients showed obvious decrement on the EDB test and no antibodies via IPA. This study shows that the EDB test correlates better with the clinical response than the antibody assays and that EDB decrement does not always correlate quantitatively with the BTXA antibody titers. In patients with secondary nonresponsiveness, it is recommended that an EDB test is the initial investigation of choice. In those patients where the EDB test does not demonstrate resistance to BTXA, a reexamination of the patients and carefully placed injections under EMG guidance may improve results.

New therapeutic indications for botulinum toxins.

The efficacy of botulinum toxin (BTX) without systemic effects has led to the rapid development of applications in neuromuscular disorders, hyperactivity of sudomotor cholinergic-mediated glandular function, and pain syndromes. The successful use of BTX in conditions with muscle overactivity, such as dystonia and spasticity, has been established and new areas in the field of movement disorders such as tics, tremor, myoclonic jerks, and stuttering has been explored with satisfactory results. Strategies to temporarily inactivate muscle function after orthopaedic or neurosurgery have also been developed. BTX treatment of hyperhidrosis was followed by its application in other hypersecretory conditions (hyperlacrimation and nasal hypersecretion) and in excessive drooling. Studies are in progress, aimed at optimising the technique and protocol of administration. Other applications for BTX have been proposed in gastroenterological and urogenital practice; it appears to be effective in replacing standard surgical procedures. Trials of BTX in painful conditions are ongoing mainly on refractory tension headache, migraine, and backache as well as dystonia-complex regional pain syndrome and myofascial pain with promising results. Recently, the fastest growing use for BTX toxin has been in the cosmetic applications. Clearly, the indications for the use of BTX are expanding, but further clinical trials will be needed in many different areas.