A Rare Case of Anti-Caspr2 Autoimmune Encephalitis Associated with a Testicular Mixed Germ Cell Tumor

Paraneoplastic limbic encephalitis (PLE) is a poorly understood condition, thought to be caused by the cross-reacting of tumor antibodies with neurons in the brain, resulting in neuropsychiatric sequelae, such as personality and behavioral changes, psychosis, memory loss, and seizures. Anti-contactin-associated protein-like 2 (CASPR2) antibodies can cause PLE in patients with particular tumors, which in most cases can be identified as thymoma, lung cancer, or endometrial cancer. Some case reports show rare instances with other tumors, such as throat or sigmoid carcinoma. We present the first reported case of CASPR2-antibody encephalitis secondary to a testicular mixed germ cell tumor.