Paraneoplastic Limbic Encephalitis in a Patient with Primary Well-differentiated Teratoma and Metastatic Poorly Differentiated Embryonal Carcinoma

Testicular tumors account for 1-2% of all tumors in men, with 95% of these being germ cell tumors. Paraneoplastic limbic encephalitis is a rare sequela of testicular tumors associated with anti-Ma2 and KLH11 antibodies. The most effective treatment for paraneoplastic limbic encephalitis is treatment of the primary malignancy. We report a 41-year-old male that presented to the emergency department with episodic alteration of consciousness and memory disturbances. Negative neurologic evaluation and imaging led to concern for a paraneoplastic process from a distant malignancy. CT imaging revealed an enlarged, necrotic para-aortic lymph node and subsequent ultrasound demonstrated a right-sided testicular mass. Right radical orchiectomy was performed. Microscopically, the mass consisted of mixed respiratory epithelium, gastrointestinal glands, and squamous epithelium with keratinization consistent with a post-pubertal testicular teratoma with associated in situ germ cell neoplasia. Resection of the para-aortic mass revealed large anaplastic cells with epithelioid features, nuclear pleomorphism and frequent mitoses. Immunostaining was positive for Pan-Keratin and OCT4, consistent with poorly differentiated embryonal carcinoma. Resection of the primary and metastatic disease, as well as treatment with corticosteroids, resulted in resolution of the encephalitis. This presentation of severe neurological disturbances in the setting of a metastatic mixed non-seminomatous germ cell tumor represents a rare presentation of paraneoplastic limbic encephalitis.