Where There's Smoke, There's Fire: Paraneoplastic Autoimmune Limbic Encephalitis

Autoimmune encephalitis can be stemmed from paraneoplastic, drug-induced, post-infectious, and idiopathic etiologies. It is often but not always associated with neuronal cell surface or intracellular antigens. Regarding encephalitis in the limbic system, the patients mostly present with impairment of cognitive functions with subacute presentation, changes in personalities, memory loss, and seizures. We present a case of a patient who presented with subtle neurological symptoms and later progressed to refractory focal epileptic activities, posing a characteristic sign of limbic encephalitis. He was later diagnosed with small cell lung cancer on further workup. This case poses a classical yet challenging diagnostic puzzle alongside education on how to disentangle patients presenting with de novo neurological signs and symptoms with unremarkable initial screening assessments and investigations in acute settings.