A Case of Anti-Caspr2 Autoimmune Encephalitis Associated with Adenocarcinoma of the Lung

Autoimmune encephalitis (AIE) is an inflammatory brain condition with multiple aetiologies but is mainly associated with paraneoplastic syndromes. Several antibodies described in AIE are being investigated in relation to different cancers, including antibodies against Contactin-associated protein-like 2 (Caspr2), which have been associated with thymoma but very rarely with lung cancer. The authors present the case of a 72-year-old man with cardiovascular risk factors, who presented with a 3-week history of left hemichorea following a first unprovoked seizure the week before, with no other signs or symptoms. The patient was submitted to extensive aetiological investigation, testing positive for anti-Caspr2 antibodies in the cerebrospinal fluid. AIE was diagnosed after other possible causes had been excluded. A PET scan showed signs of abnormal metabolism, with a lung biopsy confirming lung adenocarcinoma. This case highlights a very rare association and the importance of a thorough aetiological investigation for neurological complaints. LEARNING POINTS • Neurological complaints require a thorough aetiological investigation, and positive findings on imaging studies must be carefully examined. • Anti-Caspr2 antibodies are classically associated with Morvan syndrome, but other neurological presentations must also be considered. • Anti-Caspr2 autoimmune encephalitis may be the primary presentation of lung adenocarcinoma.