Canine Isolated Hypoaldosteronism

A 2-year-old female neutered English bull terrier presented with a history of behavioural change (depression, lethargy, avoidance of light), a mild increase in thirst and urination and two episodes of collapse. General physical and neurological examinations were unremarkable. Initial investigations documented hyponatremia and hyperkalaemia. An adrenocorticotropic hormone (ACTH) stimulation test excluded hypocortisolism. Aldosterone concentrations obtained pre- and post-ACTH stimulation were both undetectably low. Paired renin and aldosterone assays confirmed hyperreninemic hypoaldosteronism.The patient was treated with oral mineralocorticoid supplementation which resulted in a rapid improvement in both clinical signs and electrolyte concentrations; she remained well on treatment during a 5-year follow-up period.Isolated hypoaldosteronism is infrequently reported in the dog but should be considered in cases where hypoadrenocorticism is suspected based on electrolyte abnormalities, but hypocortisolism has been excluded.