Opsoclonus-myoclonus-ataxia syndrome associated with ovarian teratoma: a case report

Abstract

Case Presentation: A previously healthy 33-year-old female patient was admitted with a subacute onset of extremity tremors, imbalance, and vomiting. Neurological examination revealed gaze-evoked nystagmus, global ataxia, polyminimyoclonus, and opsoclonus. Given the clinical picture of opsoclonus-myoclonus-ataxia syndrome, an investigation for a paraneoplastic etiology was initiated. Abdominal computed tomography showed a cystic adnexal mass in the ovary. The patient underwent surgery, and the anatomopathological findings confirmed a mature ovarian teratoma. There was transient neurological improvement, followed by symptom relapse two days after resection. Cerebrospinal fluid (CSF) analysis revealed negative panels for onconeural and cell-surface antibodies, but demonstrated the presence of intrathecal IgG synthesis, which generally reflects intrathecal immunoglobulin production, suggesting an active inflammatory or autoimmune process in the central nervous system. Based on the neurological presentation and the tumor context, the hypothesis of a paraneoplastic syndrome was maintained despite the negative autoantibodies. The patient was treated with methylprednisolone pulse therapy (1g/day) combined with intravenous immunoglobulin (0.4g/kg/day) for five days, progressing with significant symptomatic improvement and functional recovery. Discussion: Opsoclonus-Myoclonus Syndrome is a rare neuroinflammatory disorder affecting the brainstem and cerebellum. In adults, its etiology is predominantly idiopathic, post-infectious, or paraneoplastic. In the oncological context, it is frequently associated with small-cell lung carcinomas, breast cancer, and ovarian teratomas. The pathophysiology involves a cross-reactive immune response (molecular mimicry) between tumor and central nervous system antigens. According to the literature, the absence of classic onconeural antibodies in the serum or CSF does not exclude the diagnosis. In these scenarios, findings such as intrathecal IgG synthesis become essential to corroborate the immune-mediated nature of the disease. Optimal management requires a dual approach: eradication of the trigger (tumor resection) and suppression of the immune response. The early postoperative relapse and the robust response to corticosteroid therapy and IVIG illustrate the clinical course of severe cases, where merely removing the tumor is insufficient to halt the autoimmune cascade. Final Comments: This is a classic paraneoplastic syndrome associated with a mature ovarian teratoma. Despite negative autoantibody serology, the clinical evolution, evidence of intrathecal IgG synthesis, tumor presence, and excellent response to combined immunotherapy strongly support the diagnosis. This case reinforces the importance of a high index of clinical suspicion for paraneoplastic neurological syndromes in the face of subacute movement disorders, highlighting that oncological investigation and early immunotherapy should not be delayed by the absence of specific biomarkers.