Inherited tubulopathies: SAQ

This neonate has antenatal Bartter syndrome. The polyhydramnios from fetal polyuria, the prematurity, the hypokalaemic hypochloraemic metabolic alkalosis, the raised urine calcium-to-creatinine ratio and the medullary nephrocalcinosis together are the classical presentation of an inherited defect of salt reabsorption in the thick ascending limb of the loop of Henle. The low blood pressure confirms a salt-losing rather than a sodium-retaining tubulopathy. [1]

Question 1 (10 marks)

Outline your immediate neonatal management and your medium-term surveillance plan for this child. [1]

The immediate priority is to correct the volume, potassium and magnesium deficits safely. I would establish intravenous access and give cautious fluid and salt replacement with normal saline, because the salt wasting is the driver of the polyuria and the alkalosis. I would correct the hypokalaemia with potassium chloride and check and replace the magnesium, because the potassium will not correct and stay corrected if the magnesium is low. I would monitor weight, strict fluid input and output, and serial electrolytes frequently, because the salt and potassium losses in antenatal Bartter are large and dynamic. [1]

The defining medical therapy for antenatal Bartter is a prostaglandin synthesis inhibitor, because the salt-losing state drives a marked prostaglandin E2 excess that worsens the polyuria, the salt wasting and the fever. I would start indometacin or ibuprofen at 1 to 3 mg per kg per day once the ductal and renal status is assessed, titrated to the response, and I would add a potassium-sparing diuretic such as amiloride or spironolactone to reduce the potassium wasting. Oral potassium chloride and magnesium would replace the ongoing losses. [5]

For the medium-term surveillance, I would confirm the diagnosis genetically with a Bartter gene panel covering SLC12A1, KCNJ1, CLCNKB and BSND, because the subtype determines the prognosis and the extrarenal features. I would arrange a hearing assessment, because the BSND subtype carries sensorineural deafness. I would monitor growth closely, because growth failure is the marker of under-treatment, and the renal ultrasound for nephrocalcinosis and stone formation. Serial electrolytes, the urine calcium-to-creatinine ratio, and blood pressure would guide the titration of the potassium, magnesium and prostaglandin synthesis inhibitor through growth, and I would involve the paediatric nephrology team for long-term care. [3]