Primary hyperaldosteronism: expanding the diagnostic net

Abstract

Practical relevance: Primary hyperaldosteronism is probably the most common adrenocortical disorder in cats. As in humans, it is often unrecognised, which excludes a potentially large number of cats from appropriate treatment.

Patient group: Affected cats present at a median age of 13 years (range 5-20 years). A breed or sex predilection has not been documented. The excessive secretion of mineralocorticoids usually leads to hypokalaemia and/or systemic arterial hypertension. Most affected cats present with muscular weakness and/or ocular signs of arterial hypertension.

Diagnostics: In any cat presenting with hypokalaemia and/or arterial hypertension, other potential causes should be excluded. The ratio of plasma aldosterone concentration to plasma renin activity (aldosterone:renin ratio) is currently the best screening test for feline primary hyperaldosteronism. Diagnostic imaging is required to differentiate between adrenocortical neoplasia and bilateral hyperplasia, and to detect any distant metastases.

Clinical challenges: The differentiation between adrenocortical neoplasia and bilateral hyperplasia is imperative for planning optimal therapy, but the limited sensitivity of diagnostic imaging may occasionally pose a problem. For confirmed unilateral primary hyperaldosteronism, unilateral adrenalectomy is the treatment of choice, and offers an excellent prognosis, but potentially fatal intra- and postoperative haemorrhage is a reported complication and risk factors have yet to be identified.

Evidence base: Only a few case reports are available on which to base the optimal diagnostic and therapeutic approach to feline primary hyperaldosteronism. This article reviews the physiology of aldosterone production and the pathophysiology of primary hyperaldosteronism, and summarises the currently available literature on the feline disease. Practical suggestions are given for the diagnostic investigation of cats with suspected primary hyperaldosteronism.

FIG 2

Blindness and muscular weakness in a cat with hypokalaemia associated with primary hyperaldosteronism. The plasma aldosterone concentration was 550 pmol/l, plasma renin activity was 45 fmol/l/sec, and the aldosterone:renin ratio was 12.2. Abdominal ultrasonography revealed an enlarged right adrenal gland

FIG 3

Four of the clinical and laboratory findings in 40 cats with presumed or confirmed primary hyperaldosteronism

FIG 4

Adrenal of a hypokalaemic cat with multiple cortical hyperplastic nodules (asterisks). Note the pre-existing zona glomerulosa of the adrenal gland (arrow). Haematoxylin and eosin stain

FIG 5

Histological section of an expansile neoplasm (asterisk) of the adrenal cortex in a cat with primary hyperaldosteronism. Note the compression of the pre-existing adrenal medulla (arrowhead). There is no marked atrophy in the uncompressed areas of the pre-existing adrenal cortex (arrow). Haematoxylin and eosin stain

Ultrasonographic image of the left adrenal gland of a cat with primary hyperaldosteronism. The gland appears to be enlarged and hyperechogenic