Normotensive primary hyperaldosteronism due to an adrenocortical adenoma in a dog

We present an 8-year-old poodle with polyuria, polydipsia and muscle weakness. Physical examination revealed no abnormalities. Laboratory alterations were hypokalemia and hypernatraemia with a low urine specific gravity. Abdominal ultrasound revealed a nodule in the right adrenal gland (diameter 0.95 cm). Systolic blood pressure was normal for several consecutive days (on average 120 mmHg). Elevated plasma aldosterone and undetectable plasma renin concentrations were diagnostic of primary hyperaldosteronism. An uncomplicated adrenalectomy was performed. Histopathological examination revealed an adrenocortical adenoma with positive expression for neuron-specific enolase but not for synaptophysin and chromogranin on immunohistochemistry. In addition, immunostaining for neuron-specific enolase was also found in cells from the normal glomerular zone of the same adrenal gland. Therefore, zona glomerulosa origin of the neoplasm was inferred. Adrenalectomy normalised laboratory abnormalities with remission of clinical signs. This report highlights the importance of not excluding the diagnosis of primary hyperaldosteronism in the absence of arterial hypertension.