Pyridostigmine-induced complete atrioventricular block in a patient with Musk antibody-negative myasthenia gravis a case report : Pyridostigmine-ind advanced AV block in MG patient with MuSK-neg.

Abstract

Background: Myasthenia gravis (MG) is a rare autoimmune neuromuscular disorder in which autoantibodies impair neuromuscular junctions. MG can be associated with thymoma and with antibodies to the acetylcholine receptor (AChR), and is less commonly associated with antibodies to muscle-specific tyrosine kinase (MuSK). Treatment of AChR antibody-positive myasthenia gravis with the cholinesterase inhibitor, pyridostigmine, has known cardiac conduction side effects. Some reports indicate these cardiac effects, including bradyarrhythmias, occur more often with MuSK-ab positive MG. This report is of a 62-year-old man with recent onset muscle-specific tyrosine kinase (MuSK)-negative thymomatous myasthenia gravis presenting with bradycardia due to pyridostigmine-associated atrioventricular (AV) block.

Case report: A 62-year-old man presented with fluctuating muscle weakness, unilateral ptosis, mild dyspnea, and mild dysphagia. Laboratory testing was positive for acetylcholine receptor antibodies (AChR-ab), but negative for MuSK antibodies. Due to his symptoms, treatment with intravenous immunoglobulin (IVIg) and pyridostigmine was initiated. Mediastinal computed tomography scan (CT scan) revealed a thymoma. During thymectomy surgery, the patient experienced intraoperative asystole. After he was stabilized, episodes of high-degree atrioventricular (AV) block were seen on postoperative ambulatory rhythm monitoring. Therefore, a permanent pacemaker (PPM) was implanted before repeat thymectomy, which was performed without complications Histopathological examination of the thymic tissue demonstrated a type B1 thymoma.

Conclusion: This report has highlighted the importance of accurate diagnosis of MG and its autoimmune subtypes, and if treatment is required with pyridostigmine, the importance of follow-up and electrocardiographic monitoring to ensure the rapid diagnosis and management of cardiac conduction abnormalities, even if they are MuSK antibody-negative.