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

While myasthenia gravis (MG) is commonly associated with thymic abnormalities and other autoimmune diseases, its association with malignancies, particularly lung adenocarcinoma, is exceptionally rare.

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.

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.

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.