Idiopathic SIADH in the premature newborn, a case report

BACKGROUND: Hyponatremia is a common laboratory finding in premature and ill neonates. When the degree of hyponatremia is more severe, the likelihood of a pathologic entity increases. In this case report we describe a premature neonate with severe hyponatremia due to the idiopathic syndrome of inappropriate antidiuretic hormone secretion (SIADH). CASE DESCRIPTION: The patient is a male neonate, born prematurely. He was admitted to the neonatal intensive care unit and received non-invasive respiratory support. After 48 hours of life serum sodium (Na(+)) decreased to 115 mmol/l. Hyponatremia progressively worsened despite aggressive Na(+) supplementation. The clinical and laboratory data were most consistent with severe SIADH. Fluid restriction was initiated which resulted in a gradual normalization of Na(+). A causal factor for development of SIADH could not be identified. CONCLUSION: When a neonate presents with significant hyponatremia that is not responsive to conventional therapy, it is important to perform a diagnostic work-up for SIADH, even in the absence of overt triggering factors.