Lambert–Eaton myasthenic syndrome presenting with occult mediastinal small cell carcinoma and positivity for anti-CV2/CRMP5 and anti-SOX1 antibodies - a case report

Sep 28, 2026

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Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune neuromuscular disorder marked by proximal weakness, autonomic dysfunction, and hyporeflexia. Although LEMS is frequently linked to anti-SOX1 antibodies and small cell carcinoma, cases showing dual antibody positivity with cerebellar ataxia plus small cell carcinoma are uncommon. A 56-year-old woman with progressive limb weakness developed mediastinal small cell lung cancer one year later and improved after combined immunotherapy and subsequent oncology follow-up.

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Abstract

Background

Case presentation

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Wang et al. BMC Neurology (2026) 26:3 [https://doi.org/10.1186/s12883-025-04541-6](https://doi.org/10.1186/s12883-025-04541-6) BMC Neurology CASE REPORT Open Access Lambert–Eaton myasthenic syndrome presenting with occult mediastinal small cell carcinoma and positivity for anti-CV2/CRMP5 and anti-SOX1 antibodies: a case report Anna Wang 1†, He Li2†, Dewen Li3, Kangfeng Wang2* and Lijuan Zhang4* Abstract Background Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune neuromuscular disorder characterized by proximal muscle weakness, autonomic dysfunction and hyporeflexia. Numerous studies have reported the association of LEMS with anti-SOX1 antibodies and small cell carcinoma, but LEMS with double antibody positivity and cerebellar ataxia accompanied by small cell carcinoma is relatively rare. Case presentation A 56-year-old female patient developed progressive limb weakness in November 2023, with symptoms gradually worsening over six months to include gait instability, impaired grip, chest tightness, dyspnea, dysphagia, and aspiration. Electrodiagnostic testing confirmed Lambert-Eaton myasthenic syndrome (LEMS) with positive VGCC antibodies. Paraneoplastic antibody testing showed positive anti-CV2/CRMP5 antibodies (24 AU) and borderline anti-SOX1 antibodies (9 AU), while other antibodies were negative. Initial imaging (contrast-enhanced chest CT and PET-CT) revealed no abnormalities, but follow-up one year later detected mediastinal small cell lung cancer. The patient underwent three plasma exchange sessions with corticosteroid therapy with limited response, then showed significant improvement after switching to subcutaneous Telitacicept (80 mg) combined with Fampyra Comprimidos and Mycophenolate Mofetil capsules, achieving independent ambulation and normal grip strength with only mild residual limb weakness. The patient has since been transferred to a local hospital for chemotherapy. Conclusion We find that LEMS with concurrent anti-SOX1 and anti-CV2/CRMP5 positivity manifests as rapid progression, prominent proximal weakness, and potential cerebellar and autonomic involvement. Early and sustained oncological surveillance—particularly of mediastinal lymph nodes—and combined immunotherapeutic strategies can significantly improve neurological outcomes. Keywords Lambert–Eaton myasthenic syndrome, Case report, Occult mediastinal small cell carcinoma, Cerebellarataxia †Anna Wang and He Li are contributed equally to this work. *Correspondence: Kangfeng Wang [wkf6@163.com](wkf6@163.com)[ ](wkf6@163.com)Lijuan Zhang [zhlj-8103@163.com](zhlj-8103@163.com) 1First School of Clinical Medicine, Shandong University of Traditional Chinese Medicine, Jinan 250014, China 2Neurology Department, Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan 250014, China 3Shandong Academy of Agricultural Sciences Health Service Center, Jinan 250014, China 4Psychosomatic Medicine, Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan 250014, China © The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly fro

FAQs

What autoimmune features define Lambert–Eaton myasthenic syndrome in this report?

LEMS is described as a rare autoimmune neuromuscular disorder with proximal muscle weakness, autonomic dysfunction, and hyporeflexia.

How was the occult mediastinal small cell carcinoma identified?

Initial contrast-enhanced chest CT and PET-CT showed no abnormalities, but follow-up one year later detected mediastinal small cell lung cancer.

What treatment changes led to clinical improvement?

After limited response to plasma exchange and corticosteroids, the patient improved significantly when switched to subcutaneous Telitacicept combined with Fampyra and mycophenolate mofetil, achieving independent ambulation with mild residual weakness.

Sep 28, 2026

Uploaded by jayni