title: Paraneoplastic syndrome of inappropriate antidiuretic hormone mimicking limbic encephalitis.
abstract: OBJECTIVE
  To compare the features of paraneoplastic syndrome of inappropriate antidiuretic hormone with those of limbic encephalitis.
  
  
  METHODS
  Case study.
  
  
  METHODS
  Academic medical center.
  
  
  METHODS
  A 46-year-old woman with progressive memory impairment, hyponatremia, and seizures.
  
  
  METHODS
  Magnetic resonance imaging of the brain, fluoro-2-deoxyglucose positron emission tomography of the body, and immunohistochemical analysis of a resected tumor.
  
  
  RESULTS
  Though the patient presented with clinical features of classic limbic encephalitis, magnetic resonance imaging, electroencephalogram, and cerebrospinal fluid analysis findings were unremarkable. Her chronic hyponatremia was ultimately found to be due to ectopic secretion of antidiuretic hormone by a neuroendocrine tumor with Merkel cell carcinoma phenotype.
  
  
  CONCLUSIONS
  Patients presenting with memory impairment, seizures, and hyponatremia should undergo a thorough workup for occult malignancy. In addition to considering classic immune-mediated paraneoplastic limbic encephalitis, the ectopic secretion of antidiuretic hormone should be included in the differential diagnosis.
authors.affiliation: Department of Neurology, Yale University School of Medicine, PO Box 208018, 15 York St, LCI-9, New Haven, CT 06520-8018, USA. nicholas.blondin@yale.edu
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Blondin
authors.forename: Alexander O
authors.initials: AO
authors.lastname: Vortmeyer
authors.forename: Noam Y
authors.initials: NY
authors.lastname: Harel
mesh_terms: D001932:Brain Neoplasms / Q000150:complications* / Q000473:pathology; D015266:Carcinoma, Merkel Cell / Q000150:complications / Q000473:pathology; D003937:Diagnosis, Differential; D004701:Endocrine Gland Neoplasms / Q000150:complications* / Q000175:diagnosis; D005260:Female; D006801:Humans; D007177:Inappropriate ADH Syndrome / Q000150:complications* / Q000175:diagnosis*; D020363:Limbic Encephalitis / Q000175:diagnosis*; D008569:Memory Disorders / Q000503:physiopathology; D008875:Middle Aged