Panhypopituitarism as the first sign of paraneoplastic limbic encephalitis in a patient with cured testicular cancer: a case report

BACKGROUND: Paraneoplastic limbic encephalitis is a rare neurologic syndrome that affects patients with cancer and commonly presents with symptoms of personality changes, visual disturbances, seizures, vertigo, and memory loss. It has an immune-mediated pathophysiology and is associated with antibodies directed against both the tumor and limbic structures in the nervous system. Here, we report a case of paraneoplastic limbic encephalitis with an unusual presentation with initial symptoms of panhypopituitarism. CASE PRESENTATION: A 28-year-old Caucasian man with history of testicular cancer in remission for almost 2 years was admitted to our hospital for altered mental status, syncope, vertical gaze palsy, ataxia, and tremor. Three months prior to admission, he began to have initial symptoms of fatigue, weight gain, and hypogonadism. A few weeks before admission, he also developed worsening neurological symptoms that led him to present to the hospital. While hospitalized, he had an episode of syncope. Evaluation of his syncope revealed that he was hypovolemic due to polyuria, concerning for diabetes insipidus. While the patient did not meet criteria for diabetes insipidus, further endocrine laboratory testing to evaluate his central hormonal axes revealed panhypopituitarism. He also underwent a neurologic work-up with brain magnetic resonance imaging and lumbar puncture, with results consistent with encephalitis. He received high-dose steroids, plasmapheresis, and intravenous immunoglobulin, which did not significantly improve his physical examination or mental status. Extensive testing did not show any recurrence of his testicular cancer. Paraneoplastic antibodies were also ordered, with anti-Ma2 antibodies eventually returning positive, consistent with anti-Ma2 paraneoplastic limbic encephalitis. CONCLUSION: Paraneoplastic limbic encephalitis is often a difficult diagnosis due to its variable presentation and timeline of presentation, leading to delays in both diagnosis and treatment. While paraneoplastic limbic encephalitis usually presents with neurological symptoms, it may also present with panhypopituitarism. A high index of suspicion is warranted for paraneoplastic syndromes in patients with history of malignancy, even if the malignancy is in remission.