Thymopentin-Induced Myasthenia Gravis: A Case Report Highlighting Clinical Vigilance

Myasthenia gravis (MG) is an autoimmune disorder of neuromuscular transmission in which the thymus plays a pivotal role in the breakdown of immune tolerance.1 We report the case of a 75-year-old Chinese woman with a history of triple-negative breast cancer (TNBC) who developed MG following the administration of thymopentin.The patient was initially diagnosed with early-stage TNBC in 2017 and underwent a modified radical mastectomy followed by adjuvant chemotherapy with the AC-T regimen.Because of persistent lymphopenia, intermittent thymopentin therapy was initiated in April 2019 (at 10 mg every other day, 14 doses per course), with courses administered every six months.During the first few days of each treatment cycle, the patient experienced transient dizziness and a sensation of heaviness, both of which resolved spontaneously without intervention.Notably, a clear temporal association was observed between thymopentin administration and the onset or exacerbation of neurological symptoms.After a scheduled course of thymopentin in October 2023, the patient first developed intermittent right-sided ptosis.Subsequently, two episodes of marked clinical deterioration were documented.In April 2024, she experienced worsening ptosis accompanied by chewing weakness, and in October 2024, she developed progressive neck weakness and dysphagia.Importantly, each episode occurred shortly after the completion of a thymopentin treatment course.