title: Reset osmostat: a rare cause of hyponatraemia.
abstract: Neonatal hyponatraemia is common, and related to significant morbidity and mortality. We report a case of a preterm newborn (gestational age of 36 weeks) with hyponatraemia, and with a prenatal diagnosis of cleft lip and palate, with a normal fetal karyotype. On the seventh day of life, a biochemical evaluation for jaundice and mild signs of dehydration showed hyponatraemia of 124 mmol/L. Investigation showed normal adrenal and thyroid functions, plasma hyposmolality (258 mOsm/kg); high urinary sodium (73 mmol/L) and high urinary osmolality (165 mOsm/kg). Despite oral sodium supplementation and fludrocortisone treatment, sodium levels remained between 124 and 130 mmol/L. Cranial ultrasound, brain MRI and renal ultrasound were normal. The diagnosis of hyponatraemia was unpredicted and the investigation was suggestive of reset osmostat, a subtype of the syndrome of inappropriate secretion of antidiuretic hormone, characterised by a subnormal threshold for antidiuretic hormone secretion.
authors.affiliation: Hospital Pediátrico, Centro Hospitalar Universitário de Coimbra, Portugal.
authors.forename: Beatriz Maia
authors.initials: BM
authors.lastname: Vale
authors.affiliation: Maternidade Bissaya Barreto do Centro Hospitalar Universitário de Coimbra, Coimbra, Portugal.
authors.forename: Sofia
authors.initials: S
authors.lastname: Morais
authors.affiliation: Maternidade Bissaya Barreto do Centro Hospitalar Universitário de Coimbra, Coimbra, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Mesquita
authors.affiliation: Maternidade Bissaya Barreto do Centro Hospitalar Universitário de Coimbra, Coimbra, Portugal.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Mimoso
mesh_terms: D000893:Anti-Inflammatory Agents / Q000627:therapeutic use; D003681:Dehydration / Q000175:diagnosis / Q000209:etiology; D005438:Fludrocortisone / Q000627:therapeutic use; D006801:Humans; D007010:Hyponatremia / Q000188:drug therapy / Q000209:etiology*; D007177:Inappropriate ADH Syndrome / Q000150:complications* / Q000175:diagnosis; D007231:Infant, Newborn; D007565:Jaundice / Q000175:diagnosis / Q000209:etiology; D008279:Magnetic Resonance Imaging; D008297:Male; D009994:Osmolar Concentration; D047928:Premature Birth; D012964:Sodium / Q000097:blood; D014667:Vasopressins / Q000378:metabolism*
chemical_list: D000893:Anti-Inflammatory Agents; D014667:Vasopressins; D012964:Sodium; D005438:Fludrocortisone