Salt-losing nephropathy associated with inappropriate secretion of atrial natriuretic peptide – a new clinical syndrome

A state of normokalemic renal sodium wasting associated with an apparently inappropriate secretion of atrial natriuretic peptide (ANP) has not been previously recognized. We here report an 11-year-old boy who presented with a chronic “salt-losing” nephropathy manifested by normonatremic or mildly hyponatremic extracellular fluid volume depletion, hypodipsia, absence of salt appetite, normokalemic metabolic alkalosis, hyper-reninemic hyperaldosteronism, hypertrophy of the juxtaglomerular apparatus, and highly conserved capacities for concentrating diluting the urine. Plasma ANP values were paradoxically elevated (between 10 and 47 fmol/ml), despite the coexistence of intravascular volume depletion and increased plasma levels of renin and aldosterone. Although the patient had some clinical similarities to Bartter’s syndrome, fractional sodium chloride (NaCl) reabsorption during hypotonic saline diuresis was normal and no clinical amelioration was observed while on indomethacin therapy. Neither a tumor nor cardiac or cerebral abnormalities, which could be responsible for the increased ANP secretion, were detected. These clinical, biochemical, and histological features have not been previously described together and may represent a new clinical syndrome. The pathophysiology of this entity remains unknown, but an attractive, although unproven, hypothesis is that the renal defect in NaCl reabsorption in this patient could be related to an inappropriate and unregulated secretion of ANP.