ESPN 51th Annual Meeting

ESPN 2018


 
High protein for low salt
SARAH MARGARET ROY 1 AMANDA NEWNHAM 1 PALLAVI YADAV 1 KAY TYERMAN 1 DETLEF BOCKENHAUER 2 TALAT MUSHTAQ 1 HITESH PRAJAPATI 1

1- LEEDS CHILDRENS HOSPITAL
2- GREAT ORMOND STREET HOSPITAL FOR CHILDREN
 
Introduction:

Hyponatraemia is commonly seen in infants. It often results from gastrointestinal losses but less frequently can be caused by endocrine or renal pathology. We present a male infant with faltering growth and severe hyponatraemia. Investigations suggested an excess of water and genetic testing demonstrated a hemizygous mutation in the AVPR2 gene establishing a diagnosis of nephrogenic syndrome of inappropriate antidiuresis (NSIAD). We present management of our patient through increasing dietary protein intake. 

Material and methods:

An 18 day old breast fed male infant presented with faltering growth but no signs of hypovolaemia. He was found to be hyponatraemic (114mmol/L) with a normal potassium and renal function. Serum osmolality was 233mosmol/kg with an inappropriately elevated urine osmolality (214mosmol/kg). Plasma aldosterone was 1032 pmol/l with a suppressed plasma renin of <0.2nmol/l/hour.  

Endocrine investigations excluded adrenal disorders (normal Synacthen test, urine steroid profile and 17-hydroxyprogesterone). Copeptin (marker for vasopressin) was in the low normal range at 2.9pmol/l.  A heavy generalised aminoaciduria was identified but there was no other evidence of proximal tubular dysfunction. Renal ultrasound scan and magnetic resonance imaging of the brain were normal.

Results:

Sodium levels improved (126mmol/L) with fluid restriction. Maintaining the fluid restriction was challenging so a vasopressin receptor antagonist (Tolvaptan) was commenced and increased to a maximum dose of 0.6m/kg/day.  This allowed some relaxation of the fluid restriction but hyponatraemia persisted (123-125mmol/L). We attempted to increase diuresis by increasing the osmotic load through a high dietary protein intake of 6g/kg/day. This improved the sodium to 133mmol/L. Currently our patient is on oral urea, with normal sodium levels and gaining weight.

Conclusions:

NSIAD is a rare genetic condition caused by a gain of function mutation in the gene encoding for the vasopressin receptor. Management with oral urea is described in the literature but we report near normalisation of sodium levels with increasing dietary protein alone.