ESPE Abstracts

Background: Hyponatremia is defined as a serum sodium level below 135 mEq/l. It is associated with increased morbidity and mortality. Hyponatremia has many causes and can be classified as acute/chronic or hypo/hypo/euvolemic. The main rule in fluid and electrolyte disorders (and especially in hyponatremia) is excluding hypothyroidism and hypocortisolism and then making the correct diagnosis. Hypothyroidism and hypocorticolism can also cause euvolemic chronic hyponatremia but the most common cause is the Syndrome of Inappropriate Anti Diuretic Hormone Secretion (SIADH). We present a case who developed the SIADH subtype reset osmostat secondary to hydrocephaly where the hyponatremia continued postoperatively and GH deficiency was also diagnosed during follow-up as we did not come across any similar cases in the literature.

Case presentation: A male patient aged 6 years and 3 months was brought for short stature and was found to have isolated hyponatremia (131.6 mEq/l) without findings of dehydration or edema in addition to the pathological short stature. Hypothyroidism and hypocortisolism were excluded. The plasma osmolarity was low (271.3 mosm/kg) and urinary sodium was high (251.6 mmol/l). The sodium level continued within the 128.1–133.2 mEq/l range despite oral sodium and fludrocortisone treatment. Hypophysis and brain MR revealed hydrocephaly due to pressure from a suprasellar arachnoid cyst. Ventriculocystocisternostomy was performed through the endoscopic route. Postoperative serum sodium levels were in the 128–132 mEq/l range and there was no percentile increase in growth. The response to GH stimulation tests was inadequate and the patient was put on GH treatment with a diagnosis of GH deficiency.

Conclusion: The discovery of the cation canal protein Transient Receptor Potential Vanilloid (TRPV) that regulates the neuronal response to systemic tonicity changes has enabled a new approach to SIADH and reset osmostat cases. Further research on the TRPV gene will perhaps clarify the relationship between chronic hyponatremia and growth retardation. We present a rare case with reset osmostat and GH deficiency due to hydrocephaly where the reset osmostat continued even after the etiology was treated and discuss the current knowledge on water metabolism in the light of new developments.