Herpes Simplex Virus Diencephalitis Leading to Panhypopituitarism.

Herpes simplex virus (HSV) is one of the most common causes of viral encephalitis. Hypothalamic-pituitary dysfunction has rarely been reported in HSV encephalitis, with few reports into the longer term outcomes for these patients. A 46-year-old male presented with a 10-day history of delirium, fever, and polydipsia. Initial computed tomography of the brain and cerebrospinal fluid cell counts were normal. Magnetic resonance imaging showed T2-hyperintensity affecting bilateral infundibuli, hypothalami, subthalamic nuclei, and optic radiations. Serial cerebrospinal fluid detected HSV1 DNA and we diagnosed him with HSV diencephalitis. He had marked biochemical abnormalities from the outset, with dramatic changes in serum sodium levels. He was ultimately diagnosed with permanent central diabetes insipidus and panhypopituitarism following evidence of central hypothyroidism, hypogonadotrophic hypogonadism, and a flat cortisol response to an insulin tolerance test. Neurocognitive recovery took several months, but subtle deficits in executive function and information processing remain. Hypothalamic hyperphagia developed as well as temperature dysregulation. He requires lifelong hormonal replacement and is undergoing regular endocrine follow up. This case highlights hypothalamic-pituitary dysfunction as a rare endocrine complication of HSV diencephalitis and illustrates the complexity of managing this in the long term.