Primary hyperaldosteronism in cats: expanding the diagnostic net

Abstract

Primary hyperaldosteronism or low-renin hyperaldosteronism in cats is characterized by inappropriately high aldosterone secretion from one or both adrenal glands, with systemic arterial hypertension and hypokalemia as leading clinical manifestations. In this thesis, non-tumorous primary hyperaldosteronism is documented, the relationship between primary hyperaldosteronism and chronic kidney disease is investigated, and a new diagnostic test for primary hyperaldosteronism is described. In Chapter 3 eleven cats with primary hyperaldosteronism are reported. Bilateral nodular hyperplasia of the adrenal zona glomerulosa was confirmed histologically in three cats and suspected in the other eight. One cat developed chronic kidney disease and in several others there was progression of chronic kidney disease. Histological examination of the kidneys of two of these cats revealed severe chronic inflammatory changes in the glomeruli, interstitium and arteries. These results suggest an association between low-renin hyperaldosteronism and progressive kidney disease in cats. These findings prompted exploratory investigation of the prevalence of primary hyperaldosteronism in cats with chronic kidney disease, as described in Chapter 4. Seven (14%) of 51 cats with chronic kidney disease had an elevated plasma aldosterone-to-renin ratio (ARR), pointing to inappropriately high aldosterone secretion. This warrants the investigation for primary hyperaldosteronism in cats with chronic kidney disease. The investigation of primary hyperaldosteronism can be rather complicated. The ARR has been widely accepted as a screening test, but is associated with some practical limitations. To circumvent these limitations, measuring aldosterone in urine was explored, as described in Chapter 5. The basal urinary aldosterone-to-creatinine ratio (UACR) was determined in 42 healthy cats and one cat with a confirmed aldosterone-producing adrenocortical carcinoma. The basal UACR in the cat with primary hyperaldosteronism was within the reference range of 46.5x10-9 points to primary hyperaldosteronism; and (3) in cats with a basal UACR between 7.5x10-9 and 46.5x10-9,