Unexpected Link Between Myasthenia Gravis and Lung Adenocarcinoma: A Case Report.

Introduction: While myasthenia gravis (MG) is commonly associated with thymic abnormalities and other autoimmune diseases, its association with malignancies, particularly lung adenocarcinoma, is exceptionally rare. Case Presentation: A 65-year-old male presented with bilateral eyelid drooping, double vision, and fatigable limb weakness, alongside a 4-month history of a non-productive cough. Neurological examination revealed bilateral ptosis, sluggish pupillary reactions, and internuclear ophthalmoplegia. Investigations demonstrated elevated anti-acetylcholine receptor (AChR) antibody levels and nerve conduction studies (NCSs) consistent with MG. Imaging revealed a right middle lobe pulmonary nodule, confirmed as adenocarcinoma via fine-needle aspiration. The patient showed symptomatic improvement with pyridostigmine and prednisolone and underwent surgical resection followed by chemotherapy. Discussion: Paraneoplastic neurologic syndromes (PNSs), though rare, can manifest as MG in association with malignancies. While MG is typically linked to thymoma, this case illustrates its coexistence with pulmonary adenocarcinoma, a seldom-reported phenomenon. Cross-reactivity between autoantibodies targeting neuronal and muscle AChRs may underlie the pathophysiology, emphasizing the need to evaluate underlying malignancies in atypical MG presentations. Conclusion: Seropositive MG can present as a paraneoplastic syndrome in association with adenocarcinoma of the lung, highlighting the importance of investigating underlying malignancies in atypical or newly diagnosed autoimmune conditions.