What happened, in summary

This 76-year-old woman first came to the emergency department after a new generalized seizure. She had also developed depression and cognitive changes. Brain MRI, EEG, lumbar puncture, and testing for infectious, vascular, toxic, and metabolic causes did not show a clear explanation, and her seizures initially improved with antiepileptic treatment. Because cognitive symptoms persisted, she also underwent brain FDG PET/CT, which did not show hypermetabolic abnormalities at that time. Four weeks later, she was readmitted with treatment-resistant seizures. During evaluation for a chronic cough, chest CT found a right para-hilar lung mass. Whole-body FDG PET/CT then showed a hypermetabolic right supra-hilar lung lesion and a hypermetabolic area in the right medial temporal brain region, without a corresponding CT lesion. Endobronchial ultrasound-guided fine-needle aspiration of the right hilar lesion confirmed small-cell lung cancer. The earlier cerebrospinal fluid sample later tested positive for anti-GABAb antibodies, supporting paraneoplastic limbic encephalitis, a neurologic immune complication triggered by the cancer. She improved after Solu-Medrol, with symptom relief and stabilization, and then received combined radiochemotherapy for small-cell lung cancer. Two months later, follow-up brain MRI showed no abnormalities. A later FDG PET/CT showed complete resolution of both the right medial temporal hypermetabolism and the previously hypermetabolic right hilar lung mass. As of May 2025, she had no further seizures reported after treatment. The clinical course connected the neurologic symptoms to an immune paraneoplastic syndrome rather than a routine seizure disorder, and cancer-directed therapy was followed by resolution of the lung finding and brain-region PET abnormality.