Myasthenia gravis with thymoma-associated CRMP5/CV2 antibody-positive paraneoplastic neurological syndrome: a case report and literature review

Objective To delineate the clinical characteristics, diagnostic criteria, therapeutic strategies, and prognosis of myasthenia gravis (MG) with thymoma-associated CRMP5/CV2 antibody-positive paraneoplastic neurological syndrome (PNS), thereby enhancing clinical recognition of this rare overlapping autoimmune disorder. Methods We retrospectively analyzed the clinical data of a 53-year-old male patient presenting with peripheral nerve injury as the initial manifestation, who was subsequently diagnosed with MG, invasive thymoma, and CRMP5/CV2 antibody-positive PNS. A comprehensive review of the relevant international literature was also conducted. Results The patient had a 2-year disease course, initially presenting with limb numbness and unsteady gait, and gradually developing dysarthria, dysphagia, diplopia, and myasthenic weakness with characteristic diurnal fluctuation (worsening in the evening and improving in the morning). According to the Myasthenia Gravis Foundation of America (MGFA) clinical classification, the patient was categorized as Class IIIb (moderate generalized MG with predominant oropharyngeal involvement) at baseline. Serological tests confirmed positive for acetylcholine receptor (AChR) antibody in serum, as well as CRMP5/CV2 antibody in both serum and cerebrospinal fluid (CSF). Electrophysiological examinations revealed multiple peripheral nerve damage and a significant decremental response to low-frequency repetitive nerve stimulation (RNS). Chest CT demonstrated an invasive thymoma in the anterior mediastinum. The patient underwent thoracoscopic thymectomy, followed by sequential treatment with glucocorticoids, intravenous immunoglobulin and cyclophosphamide, as well as symptomatic supportive care and anti-infective management. After treatment, the neurological symptoms were significantly improved, and the condition remained stable during follow-up. Conclusion MG with thymoma-associated CRMP5/CV2 antibody-positive PNS represents a rare clinical entity with atypical onset and is highly susceptible to misdiagnosis. Combined detection of paraneoplastic antibodies and chest imaging is critical for early diagnosis, and thymectomy combined with standardized immunotherapy can effectively improve the clinical symptoms and long-term prognosis of patients.