Celebrating the 70 years of pyridostigmine on therapy of Myasthenia Gravis: historical aspects of the preliminary trials / Celebrando os 70 anos da piridostigmina no tratamento da Miastenia Gravis: aspectos históricos dos ensaios clínicos preliminares

Abstract Currently, pyridostigmine bromide is an indispensable anticholinesterase agent used worldwide to treat patients with Myasthenia Gravis (MG). However, pyridostigmine bromide was unsuccessful in its "pioneering trials" to treat a series of MG patients. There are important historical landmarks before pyridostigmine bromide becomes useful, safe and indispensable for MG therapy. After 70 years of these "pioneering trials", this article reviews some historical aspects related to them, as well as other preliminary trials using pyridostigmine bromide as therapy for MG patients.

Resumo Atualmente, o brometo de piridostigmina é um indispensável agente anticolinesterásico usado em todo o mundo no tratamento de pacientes com Miastenia Gravis (MG). Contudo, o brometo de piridostigmina não foi bem-sucedido, em seus "ensaios clínicos pioneiros", no tratamento de uma série de pacientes com MG. Existem importantes marcos históricos antes do brometo de piridostigmina se tornar útil, seguro e indispensável no tratamento da MG. Após 70 anos desses "ensaios clínicos pioneiros", este artigo revisa alguns aspectos históricos a eles relacionados, bem como a outros estudos preliminares que usaram o brometo de piridostigmina como um tratamento para pacientes com MG.

Miastenia Gravis: reporte de dos casos y revisión de la literatura / Myasthenia Gravis: two case reports and review

Myasthenia gravis is an acquired autoimmune disorder of the neuromuscular junction characterized by fluctuating weakness and fatigability of skeletal muscles. The diagnosis can be established by clinical and serologic testing, with predominance of autoantibodies against the acetylcholine receptor, and Muscle-specific kinase antibodies. We report two cases of Myasthenia gravis, the first one is a 31 year old patient with a debut of the disease, mainly with bulbar symptoms, and the second one is a 29 year old patient diagnosed with generalized Miasthenia Gravis also mainly with bulbar symptoms with worsening of symptomatology. In this report treatments alternatives and management approaches are discused

Síndrome miasténico congénito por deficiencia de rapsina: reporte de caso con nueva mutación y heterocigosidad compuesta / Congenital myasthenic syndrome due to rapsyn deficiency: A case report with a new mutation and compound heterozygosity

INTRODUCCIÓN Los síndromes miasténicos congénitos son un grupo heterogéneo de desórdenes genéticos, caracterizados por una transmisión sináptica anormal en la placa neuromuscular. REPORTE Presentamos el caso de un paciente de dos años, varón, con hipotonía, ptosis palpebral y debilidad simétrica y de predominio proximal, características que aparecieron desde el nacimiento y que motivaron varias hospitalizaciones por neumonía e insuficiencia ventilatoria. Desde el inicio de la deambulación a los dos años, los padres notaron que la debilidad empeoraba por las tardes y con la actividad física repetida o prolongada. El examen físico a los dos años mostró ptosis palpebral, debilidad de predominio proximal y fatigabilidad con el esfuerzo sostenido. La electro-miografía evidenció decremento del 27% en el potencial de acción muscular compuesto. El análisis de tríos mostró heterocigosis compuesta por transmisión de dos mutaciones diferentes en el gen de rapsina, una ya conocida procedente del padre y la otra no reportada previa-mente, procedente de la madre. El paciente recibió piridostigmina obteniendo mejoría inmediata y logrando un desempeño óptimo en actividades escolares, deportivas y de la vida cotidiana. A la fecha, no ha presentado nuevos episodios de insuficiencia ventilatoria. CONCLUSIONES La debilidad de inicio neonatal y la fatigabilidad o agotamiento con el esfuerzo sostenido, con afección principalmente de los músculos con inervación troncal y con un decremento mayor al 10% en el potencial de acción muscular compuesto en la electromiografía, deben hacer sospechar en un síndrome miasténico congénito. Se revisan los puntos clínicos clave que permiten establecer el diagnóstico oportuno y las opciones de tratamiento efectivo para algunos de estos síndromes.

INTRODUCTION The congenital myasthenic syndromes are a heterogeneous group of genetic disorders characterized by an abnormal synaptic transmission in the neuromuscular plate. REPORT We present a two-year-old patient, male, with hypotonia, palpebral ptosis, and proximal symmetric weakness with a neonatal onset that motivated several and prolonged hospitalizations for pneumonia and respiratory failure. From two years of age, the parents noticed that the facial and general weakness worsened in the afternoons and with repeated or prolonged physical activity. The physical examination showed palpebral ptosis, predominantly proximal weakness, and fatigability with sustained muscular effort. The electromyography showed a 27% decrement in the Compound Muscular Action Potential and the case-parents genetic study showed compound heterozygosity with the transmission of two different mutations in the rapsyn gene from both parents. The patient received pyridostigmine with great improvement, achieving optimal performance in school, sports, and daily life activities. CONCLUSIONS Weakness and fatigability with neonatal onset, mainly affecting the muscles with brain stem innervation and the decrement greater than 10 percent in the Compound Muscular Action Potential in the electromyographic studies, should make us suspect in a congenital myasthenic syndrome. We review the literature and key clinical points to establish a timely diagnosis and effective treatment in some of these syndromes.

Comparison of sugammadex and pyridostigmine bromide for reversal of rocuronium-induced neuromuscular blockade in short-term pediatric surgery: a prospective randomized study

BACKGROUND: Sugammadex reverses rocuronium-induced neuromuscular blockade quickly and effectively. Herein, we compared the efficacy of sugammadex and pyridostigmine in the reversal of rocuronium-induced light block or minimal block in pediatric patients scheduled for elective entropion surgery. METHODS: A prospective randomized study was conducted in 60 pediatric patients aged 2–11 years who were scheduled for entropion surgery under sevoflurane anesthesia. Neuromuscular blockade was achieved by administration of 0.6 mg/kg rocuronium and assessed using the train-of-four (TOF) technique. Patients were randomly assigned to 2 groups receiving either sugammadex 2 mg/kg or pyridostigmine 0.2 mg/kg and glycopyrrolate 0.01 mg/kg at the end of surgery. Primary outcomes were time from administration of reversal agents to TOF ratio 0.9 and TOF ratio 1.0. Time from the administration of reversal agents to extubation and postoperative adverse events were also recorded. RESULTS: There were no significant differences in the demographic variables. Time from the administration of reversal agents to TOF ratio 0.9 and TOF ratio 1.0 were significantly shorter in the sugammadex group than in the pyridostigmine plus glycopyrrolate group: 1.30 ± 0.84 vs. 3.53 ± 2.73 min (P < 0.001) and 2.75 ± 1.00 vs. 5.73 ± 2.83 min (P < 0.001), respectively. Extubation time was shorter in the sugammadex group. Adverse events, such as skin rash, nausea, vomiting, and postoperative residual neuromuscular blockade (airway obstruction), were not statistically different between the two groups. CONCLUSIONS: Sugammadex provided more rapid reversal of rocuronium-induced neuromuscular blockade in pediatric patients undergoing surgery than did pyridostigmine plus glycopyrrolate.

Current use of neuromuscular blocking agents and antagonists in Korea: a 2018 survey

BACKGROUND: Neuromuscular blocking agents (NMBAs) and neuromuscular monitoring in anesthetic management are integral for endotracheal intubation, better visualization of the surgical field, and prevention of residual neuromuscular blockade and pulmonary complications. Sugammadex is a drug that reduces risk of residual neuromuscular blockade, with more rapid recovery compared to anticholinesterase. The purpose of this study was to investigate current usage status of NMBAs and antagonist with neuromuscular monitoring, among anesthesiologists in Korea.METHODS: Anesthesiologists working in Korea were invited to participate in an online survey via email January 2–February 28, 2018. The questionnaire consisted of 45 items, including preferred NMBAs, antagonists, neuromuscular monitoring, and complications related to the use sugammadex. A total of 174 responses were analyzed.RESULTS: Rocuronium was a commonly used NMBA for endotracheal intubation (98%) of hospitals, and maintenance of anesthesia (83.3%) in of hospitals. Sugammadex, pyridostigmine, and neostigmine were used in 89.1%, 87.9%, and 45.4% of hospitals. Neuromuscular monitoring was employed in 79.3% of hospitals; however only 39.7% of hospitals used neuromuscular monitoring before antagonist administration. Usual dosage range of sugammadex was 2.1–4 mg/kg in 35.1% of hospitals, within 2 mg/kg in 34.5% of hospitals, and 1 vial regardless of body weight in 22.4% of hospitals. Sugammadex-related complications were encountered by 14.9% of respondents.CONCLUSIONS: This survey indicates several minor problems associated with the use of antagonists and neuromuscular monitoring. However, most anesthesiologists appear to have appropriate information regarding the usage of NMBAs and sugammadex.

General anesthesia for an adolescent with Pelizaeus-Merzbacher disease: A case report

Pelizaeus-Merzbacher disease (PMD) is a progressive and degenerative chromosomal disorder of the central nervous system caused by defective myelin production. Few case reports have been issued on the anesthetic management of PMD, because of its extremely low incidence. We anesthetized a 13-year-old female patient diagnosed with PMD for ophthalmic surgery because of intermittent exotropia. General anesthesia was induced and maintained with propofol and sevoflurane in air and oxygen. Rocuronium was administered to facilitate orotracheal intubation, and residual neuromuscular blockage was reversed with pyridostigmine. Between emergence to 24 hours postoperatively, her muscle power completely recovered and no unpredictable events occurred. Summarizing, anesthesiologists should be concerned about the high possibility of aspiration, spasticity, and seizure during the perioperative period in patients with even mild PMD. Appropriate preoperative evaluation, intraoperative monitoring, and choice of proper anesthetic drugs enable safe anesthesia in patients with PMD.

Pyridostigmine in Pediatric Intestinal Pseudo-obstruction: Case Report of a 2-year Old Girl and Literature Review

Pediatric chronic intestinal pseudo-obstruction is a rare disorder characterized by a severe impairment of gastrointestinal motility leading to intestinal obstruction symptoms in the absence of mechanical causes. The diagnosis is usually clinical and diagnostic work is usually aimed to rule out mechanical obstruction and to identify any underlying diseases. Treatment is challenging and requires a multidisciplinary effort. In this manuscript we describe the youngest child successfully treated with the orally administrable, long-acting, reversible anti-cholinesterase drug, pyridostigmine. Like other drugs belonging to cholinesterase inhibitors, pyridostigmine enhances gut motility by increasing acetylcholine availability in the enteric nervous system and neuro-muscular junctions. Based on the direct evidence from the reported case, we reviewed the current literature on the use of pyridostigmine in severe pediatric dysmotility focusing on intestinal pseudo-obstruction. The overall data emerged from the few published studies suggest that pyridostigmine is an effective and usually well tolerated therapeutic options for patients with intestinal pseudo-obstruction. More specifically, the main results obtained by pyridostigmine included marked reduction of abdominal distension, reduced need of parenteral nutrition, and improvement of oral feeding. The present case and review on pyridostigmine pave the way for eagerly awaited future randomized controlled studies testing the efficacy of cholinesterase inhibitors in pediatric severe gut dysmotility.

Gluten and Neuroimmunology. Rare association with Myasthenia Gravis and Literature Review

SUMMARY As the celiac disease (CD), the non-celiac gluten sensitivity (NCGS) has also been associated with several autoimmune manifestations. It is rarely associated with myasthenia gravis (MG). This paper shall introduce the case of a young female patient, initially presenting a peripheral neuropathy framework. During clinical and neurological follow-up, she began to present symptoms of various immune-mediated morbidities. Diseases related to gluten represent a clinical spectrum of manifestations with a trigger in common, the ingestion of gluten. CD is the most well-known and serious disease of the spectrum, also called gluten-sensitive enteropathy. The NCGS is diagnosed from clinical evidence of improvement in symptoms followed by a Gluten Free Diet (GFD) in patients without signs of enteropathy in duodenal biopsy. There are indications that, although rare, with a prevalence of 1 in 5000, myasthenia gravis (MG) may occur more often when CD is also present. Between 13 to 22% of the patients with MG have a second autoimmune disorder. However, it is often associated with dermatomyositis or polymyositis, lupus erythematosussystemic lupus erythematosus, Addison's disease, Guillain-Barré syndrome and juvenile rheumatoid arthritis. Thus, the symptoms of neuromuscular junction involvement may give a diagnostic evidence of this rare association.

Response to neuromuscular blockade with rocuronium during general anesthesia in a patient with dermatomyositis: A case report

Dermatomyositis is an idiopathic inflammatory myopathy characterized by skin changes and muscle weakness. Depending on the involvement of various muscles, dermatomyositis can cause aspiration pneumonia, ventilatory impairment, and heart failure. Several reports have documented normal or prolonged neuromuscular blockade following administration of different non-depolarizing neuromuscular blockers in patients with dermatomyositis. We observed delayed onset of blockade and prolonged recovery following administration of 0.6 mg/kg rocuronium in a patient with dermatomyositis. However, when the train-of-four ratio reached 0.3, the patient was administered pyridostigmine and glycopyrrolate, which led to normal response to reversal of rocuronium. The patient was extubated without respiratory complications. The outcomes of this case indicate that response to the usual dosage of muscle relaxants in patients with dermatomyositis might be different from that in patients without this condition. Anesthesiologists should pay attention to preoperative cardiorespiratory evaluation and intraoperative neuromuscular monitoring.

Miastenia gravis y su asociación con trastornos linfoproliferativos: casos clínicos / Myasthenia gravis and its association with lymphoproliferative disorders: a case series

Myasthenia gravis (MG) is a rare autoimmune disease of the neuromuscular junction. It is characterized by variable weakness and excessive fatigability of skeletal muscles. In the last few years, numerous reports have been published showing the association between autoimmune diseases, such as systemic erythematous lupus or rheumatoid arthritis, with lymphoid neoplasias. The association between MG and lymphoid neoplasia seems to be less frequent. To analyze this association we reviewed the MG patients in the Department of Neurology, Hospital Salvador of Santiago, Chile. During a three-year period we identified four patients who developed different lymphoproliferative disorders: two with B-cell lymphoma, one with chronic lymphocytic leukaemia and one plasmacytoma with an associated amyloidosis. The MG was generalized but mild, all cases classified as type IIa according to the definition proposed by the MG Foundation of America. The neoplasia appeared two to 36 years after the onset of MG. These cases provide additional evidence of the association between MG and lymphoproliferative disorders.

Dysphagia as the Only Manifestation of Myasthenia Gravis: A Case Report / 대한연하장애학회지

Dysphagia is a common manifestation of myasthenia gravis (MG), but it has been rarely reported as the only symptom. We report a 46-year-old man who complained of dysphagia without any other symptoms. Based on a videofluoroscopic swallowing study (VFSS), he showed decreased tongue base retraction, premature bolus loss, and incomplete velopharyngeal closure. He also showed impaired laryngeal elevation that caused incomplete laryngeal closure and aspiration with a small amount of thin fluid. Laryngoscopic evaluations, brain magnetic resonance imaging, and repetitive nerve stimulation tests were unremarkable. Since the acetylcholine receptor antibody level was elevated, he was diagnosed with MG. Treatment with pyridostigmine was initiated and the dysphagia symptoms improved completely. MG is one possible cause of unexplained dysphagia. Therefore, neurological examination is required when abnormal findings are observed in VFSS, and evaluations for MG may be important for the final diagnosis.

Use of sugammadex in lung cancer patients undergoing video-assisted thoracoscopic lobectomy / 대한마취과학회지

BACKGROUND: This study aimed to retrospectively evaluate the use of sugammadex in patients undergoing video-assisted thoracoscopic surgery (VATS) lobectomy. METHODS: Data were obtained from medical record review of patients who underwent VATS lobectomy from January 2013 to November 2014. Fifty patients were divided into two groups: the sugammadex group (group S, n = 19) was administered sugammadex 2 mg/kg, while the pyridostigmine group (group P, n = 31) received pyridostigmine 20 mg with glycopyrrolate 0.2 mg or atropine 0.5 mg. The primary endpoint measure was the overall incidence of postoperative pulmonary complications including prolonged air leak, pneumonia, and atelectasis. The secondary endpoint measures were the length of postoperative hospital stay and duration of chest tube insertion. RESULTS: The overall incidence of postoperative pulmonary complications in patients in group S was significantly lower compared with that of group P (5 [26.3%] vs. 17 [54.8%]; P = 0.049). Also, the durations of chest tube insertion (5.0 [4.0–7.0] vs. 7.0 [6.0–8.0] days; P = 0.014) and postoperative hospital stay (8.0 [8.0–10.0] vs. 10.0 [9.0–11.0] days; P = 0.019) were shorter in group S compared with group P. Administration of sugammadex was associated reduced with postoperative pulmonary complications (OR: 0.22; 95% CI: 0.05–0.87; P = 0.031). CONCLUSIONS: The use of sugammadex, compared with pyridostigmine, showed a significantly reduced overall incidence of postoperative pulmonary complications and decreased duration of chest tube use and postoperative hospital stay in patients undergoing VATS lobectomy, suggesting that sugammadex might be helpful in improving clinical outcomes in such patients.

Bulbar Myasthenia Gravis Superimposed in a Medullary Infarction Diagnosed by a Fiberoptic Endoscopic Evaluation of Swallowing With Simultaneous Tensilon Application

In the elderly, myasthenia gravis (MG) can present with bulbar symptoms, which can be clinically difficult to diagnose from other neurological comorbid conditions. We describe a case of a 75-year-old man who had been previously diagnosed with dysphagia associated with medullary infarction but exhibited aggravation of the dysphagia later on due to a superimposed development of bulbar MG. After recovering from his initial swallowing difficulties, the patient suddenly developed ptosis, drooling, and generalized weakness with aggravated dysphagia. Two follow-up brain magnetic resonance imaging (MRI) scans displayed no new brain lesions. Antibodies to acetylcholine receptor and muscle-specific kinase were negative. Subsequent electrodiagnosis with repetitive nerve stimulation tests revealed unremarkable findings. A diagnosis of bulbar MG could only be established after fiberoptic endoscopic evaluation of swallowing (FEES) with simultaneous Tensilon application. After application of intravenous pyridostigmine, significant improvement in dysphagia and ptosis were observed both clinically and according to the FEES.

Subgroup Classification and Therapeutic Guidance for Myasthenia Gravis / 대한소아신경학회지

Myasthenia gravis (MG) is a chronic autoimmune disease of neuromuscular blockade, characterized by muscle weakness and fatigue, and is associated with the production of autoantibodies against the skeletal muscle acetylcholine receptor, muscle-specific kinase (MuSK), low-density lipoprotein receptor-related protein 4 (LRP4), and other muscle endplate proteins. In addition, MG may be classified according the location of the affected muscles (ocular vs. generalized), patient age at symptom onset, and thymic pathology. Subgroup classification based on serum antibodies and clinical features include early-onset, late-onset, thymoma-associated, MuSK and LRP4 antibody-negative, and ocular forms of MG, and can help with therapeutic decisions and prognosis. Pyridostigmine is the chosen symptomatic treatment. For patients who do not adequately respond to symptomatic therapy, corticosteroids, other immunomodulating agents, and thymectomy are the first-line immunosuppressive treatments. The treatment of MG is highly individualized and depends on the age of the patient, the type and severity of the disease, and the pace of progression.

Subgroup Classification and Therapeutic Guidance for Myasthenia Gravis / 대한소아신경학회지

Myasthenia gravis (MG) is a chronic autoimmune disease of neuromuscular blockade, characterized by muscle weakness and fatigue, and is associated with the production of autoantibodies against the skeletal muscle acetylcholine receptor, muscle-specific kinase (MuSK), low-density lipoprotein receptor-related protein 4 (LRP4), and other muscle endplate proteins. In addition, MG may be classified according the location of the affected muscles (ocular vs. generalized), patient age at symptom onset, and thymic pathology. Subgroup classification based on serum antibodies and clinical features include early-onset, late-onset, thymoma-associated, MuSK and LRP4 antibody-negative, and ocular forms of MG, and can help with therapeutic decisions and prognosis. Pyridostigmine is the chosen symptomatic treatment. For patients who do not adequately respond to symptomatic therapy, corticosteroids, other immunomodulating agents, and thymectomy are the first-line immunosuppressive treatments. The treatment of MG is highly individualized and depends on the age of the patient, the type and severity of the disease, and the pace of progression.

Clinical Significance of Repetitive Compound Muscle Action Potentials in Patients with Myasthenia Gravis: A Predictor for Cholinergic Side Effects of Acetylcholinesterase Inhibitors

BACKGROUND AND PURPOSE: Acetylcholinesterase inhibitors (AChEIs) are widely used to treat myasthenia gravis (MG). Although AChEIs are usually tolerated well, some MG patients suffer from side effects. Furthermore, a small proportion of MG patients show cholinergic hypersensitivity and cannot tolerate AChEIs. Because repetitive compound muscle action potentials (R-CMAPs) are an electrophysiologic feature of cholinergic neuromuscular hyperactivity, we investigated the clinical characteristics of MG patients with R-CMAPs to identify their clinical usefulness in therapeutic decision-making. METHODS: We retrospectively reviewed the clinical records and electrodiagnostic findings of MG patients who underwent electrodiagnostic studies and diagnostic neostigmine testing (NT). RESULTS: Among 71 MG patients, 9 could not tolerate oral pyridostigmine bromide (PB) and 17 experienced side effects of PB. R-CMAPs developed in 24 patients after NT. The highest daily dose of PB was lower in the patients with R-CMAPs (240 mg/day vs. 480 mg/day, p<0.001). The frequencies of PB intolerance and side effects were higher in the patients with R-CMAPs than in those without R-CMAPs [37.5% vs. 0% (p<0.001) and 45.8% vs. 12.8% (p=0.002), respectively]. The MG Foundation of America postintervention status did not differ significantly between MG patients with and without R-CMAPs, and the response to immunotherapy was also good in both groups. CONCLUSIONS: Side effects of and intolerance to AChEIs are more common in MG patients with R-CMAPs than in those without R-CMAPs. AChEIs should be used carefully in MG patients with R-CMAPs. The presence of R-CMAPs after NT may be a good indicator of the risks of PB side effects and intolerance.

Effect of neuromuscular blockade reversal by pyridostigmine on spectral entropy values during recovery from desflurane anesthesia: a prospective, randomized, double-blind, controlled trial / 대한마취과학회지

BACKGROUND: According to several studies investigating the relationship between muscle activity and electroencephalogram results, reversal of neuromuscular blockade (NMB) may affect depth of anesthesia indices. Therefore, we investigated the effect of pyridostigmine on these indices via spectral entropy. METHODS: Fifty-six patients scheduled for thyroidectomy or parotidectomy were included in this study and randomized into two groups. At the start of skin suturing, the desflurane concentration was adjusted to 4.2 vol% in both groups. Following this, the pyridostigmine group (group P, n = 28) was administered pyridostigmine 0.2 mg/kg mixed with glycopyrrolate 0.04 mg/kg, while the control group (group C, n = 28) received normal saline. Entropy values (response entropy [RE] and state entropy [SE]), train of four (TOF) ratio, and end-tidal desflurane concentration were recorded from point of drug administration to 15 minutes post-drug administration. RESULTS: Mean RE values at 15 minutes, when the maximum effect of pyridostigmine was anticipated, showed a statistically significant difference between groups (53.8 ± 10.5 in group P and 48.0 ± 8.8 in group C; P = 0.030). However, mean SE at 15 minutes showed no significant difference between the two groups (P = 0.066). At 15 minutes, there were significant differences in the TOF ratio between the two groups (P < 0.001). CONCLUSIONS: NMB reversal by pyridostigmine significantly increased RE values but not SE values. This finding suggests that spectral entropy may be a useful alternative tool for monitoring anesthetic depth during recovery from anesthesia in the presence of electromyogram activity.

Allergic Reaction to Meperidine in a Patient with Aspirin Idiosyncrasy / 대한내과학회지

Although narcotic analgesics are potent releasers of histamine, IgE-mediated allergic reactions to these drugs are rare. Here we report the case of a 56-year-old male who suffered from chronic urticarial and analgesics-induced skin rashes. He visited our allergy clinic to determine alternative analgesics before undergoing surgery. A drug provocation test showed a positive reaction to aspirin, but negative reactions to acetaminophen and celecoxib. Despite careful attention to his drug regimen, during surgery he developed generalized urticaria and flushing. Skin tests of allergy to latex, lidocaine, propofol, rocuronium, flomoxef, meperidine, palonosetron, pyridostigmine, and fentanyl yielded negative results, except for the prick and intradermal tests with meperidine. Thus, this patient had both an aspirin/non-steroidal anti-inflammatory drugs idiosyncrasy and an IgE-mediated hypersensitivity to meperidine.

Clinical and Electrophysiologic Responses to Acetylcholinesterase Inhibitors in MuSK-Antibody-Positive Myasthenia Gravis: Evidence for Cholinergic Neuromuscular Hyperactivity

BACKGROUND AND PURPOSE: Patients with muscle-specific tyrosine kinase (MuSK) antibody (MuSK-Ab)-positive myasthenia gravis (MG) show distinct responses to acetylcholinesterase inhibitors (AChEIs). Although clinical responses to AChEIs in MuSK-Ab MG are reasonably well known, little is known about the electrophysiologic responses to AChEIs. We therefore investigated the clinical and electrophysiologic responses to AChEIs in MuSK-Ab-positive MG patients. METHODS: We retrospectively reviewed the medical records and electrodiagnostic findings of 17 MG patients (10 MuSK-Ab-positive and 7 MuSK-Ab-negative patients) who underwent electrodiagnostic testing before and after a neostigmine test (NT). RESULTS: The frequency of intolerance to pyridostigmine bromide (PB) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (50% vs. 0%, respectively; p=0.044), while the maximum tolerable dose of PB was lower in the former (90 mg/day vs. 480 mg/day, p=0.023). The frequency of positive NT results was significantly lower in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (40% vs. 100%, p=0.035), while the nicotinic side effects of neostigmine were more frequent in the former (80% vs. 14.3%, p=0.015). Repetitive compound muscle action potentials (R-CMAPs) developed more frequently after NT in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (90% vs. 14.3%, p=0.004). The frequency of a high-frequency-stimulation-induced decrement-increment pattern (DIP) was higher in MuSK-Ab-positive patients than in MuSK-Ab-negative patients (100% vs. 17.7%, p=0.003). CONCLUSIONS: These results suggest that MuSK-Ab-positive MG patients exhibit unique and hyperactive responses to AChEIs. Furthermore, R-CMAP and DIP development on a standard AChEI dose may be a distinct neurophysiologic feature indicative of MuSK-Ab-positive MG.