Paraneoplastic limbic encephalitis associated with testicular mixed germ cell tumor

Paraneoplastic limbic encephalitis (PLE) is a rare immunopathological syndrome, reported in association with certain types of malignancies. Patients present with cognitive and memory impairments, disordered perception, mood and behavioral changes, sleep disturbances, and seizures. Despite the growing number of cases being reported, it still poses a diagnostic challenge. We encountered a patient with a myriad of neuropsychiatric symptoms who exhibited a highly variable response to therapy. A 36-year-old male presented with memory impairment, excessive sleepiness, and slurred speech. Brain magnetic resonance imaging revealed hyperintensities in the temporal lobes and hypothalamus, all suggestive of limbic encephalitis. He was found to have a mixed germ cell testicular teratoma. Screening for commonly associated antibodies did not yield positive results, which emphasizes that sero-negative PLE can be missed in patients with malignancies. In reporting this case, we urge neurologists to consider PLE as part of the differential diagnosis in similar ambiguous clinical scenarios.