Whilst CKD and hyperthyroidism are the most common conditions where we see secondary hypertension in cats, I do think it's worth saying that hypertension doesn't have to be secondary to a disease process. We can diagnose hypertension secondary to administration of certain drugs. Perhaps one of the most common drugs that we think about associated with hypertension is darbapoietin.
This is an erythrocyte stimulating agent that we sometimes use in cats that have developed anaemia as a consequence of their kidney disease. Measuring blood pressure is recommended as part of routine monitoring when using this drug. But apart from drugs, have you seen hypertension in cats with disease conditions other than or hyperthyroidism?
Well, we're definitely starting to get into some of the rarer disease conditions here for sure, but it is worth just mentioning some conditions that affect the adrenal gland. A number of adrenal mass lesions can lead to the production of hormones that have been associated with hypertension. So for example, tumours of the adrenal medulla known as pheochromocytomas or cortisol secreting tumours that cause Cushing's syndrome.
But these are both very rare in cats. Still an uncommon condition, but perhaps an adrenal condition that we see slightly more often than either Cushing's syndrome or pheochromocytoma in the cat, and which does warrant mention is hyperaldosterism or C syndrome. In cats, primary hyperaldosterism is usually the result of a unilateral cortical adrenal adenoma or adenocarcinoma.
Once again, this is a condition that is most often seen in older cats, so typically cats over the age of 10, and it's a condition where we see hypertension. What do you think are the most common presenting signs for a cat with hyperaldosterism or Con syndrome? Given that cats with hyperaldotrinism can be hypertensive, it's certainly possible and it has been reported that they can present with ocular hypertensive target organ damage.
But actually, cats with Conn's syndrome most often present with clinical signs relating to their hypokalemia and associated hyperkalemic polymyopathy. They often show signs of weakness and particularly ventriflexion of the neck. The clinical index of suspicion for primary hyperaldotrinism is going to be high when we have a combination of compatible clinical signs together with the marked hypokalemia, and we identify an adrenal mass lesion, for example, on ultrasound.
But the diagnosis can be confirmed by measuring plasma aldosterin concentrations, which are typically going to be very high. Excess aldosterone can contribute to sodium retention and therefore extracellular volume expansion that increases both stroke volume and cardiac output and contributes to the development of hypertension. But the effects of aldosterone on blood pressure regulation are much more complex than this.
Either way, it's very common for us to see hypertension in cats with hyperaldotrinism, and of the cases reported in the literature, somewhere between 50 to 100% were hypertensive. So it's clearly very important to measure blood pressure if we suspect this condition. So a question for you, is there a specific management that we should use for cats with primary hyperaldosterism, or can we just use standard anti-hypertensive agents like amlodipine?
Because hyperaldosterism is having very specific effects on the body, it is important that we start medical treatment that opposes the action of excess aldosterone. So we would typically start by administering an aldosterone antagonist such as spironolactone. We usually try to improve potassium levels initially with intravenous potassium, but also oral supplementation as well.
Whilst using an aldosterone antagonist does reduce blood pressure slightly, it's typically only by around 10 millimetres of mercury. And so when cats are hypertensive with their hyperaldotrinism, we do normally need to use additional anti-hypertensive agents. In the K series in the literature, amlodipine has been widely used and seems to be well tolerated in this situation.
The goals for our antihypertensive treatment are the same for all of the other conditions, so we're looking to decrease systolic blood pressure to less than 160 millimetres of mercury and ideally under 140 millimetres of mercury, with really careful monitoring of blood pressure as well as electrolyte status. So what happens to the requirement for those anti-hypertensive medications if cats with hyperaldosterism have an adrenalectomy performed? Definitive treatment for hyperaldossterism is surgical removal of the abnormal adrenal gland.
But there's actually relatively little information in the literature about the requirements for ongoing anti-hypertensive treatment where adrenalectomy has been performed. For cats that only have primary hyperaldostrinism, then theoretically, after surgical removal of that adrenal gland, it should be possible to discontinue antihypertensive treatment. However, once again, it is important to remember that there could be other disease conditions that might also be contributing to the development of hypertension.
Because we see hyperaldosterism in older cats, it's not uncommon for them to also have other disease conditions, for example, chronic kidney disease. Where this is the case, it is possible that both age and CKD could also be contributing to that individual cat's risk of being hypertensive. So in these cats, we will often just continue antihypertensive treatment in the long term.
Thinking about some take home messages, we should remember that secondary hypertension can be secondary to an underlying disease but can also be secondary to the administration of certain drugs. Of the disease conditions associated with hypertension in cats, diseases of the adrenal glands sometimes need to be considered. And out of these, hyperaldosterism or Con syndrome is still uncommon but certainly can be diagnosed.
For cats with hyperaldosterism, we prescribe an aldosterone antagonist such as spironolactone together with potassium supplementation. But if the cat is hypertensive, we usually also need to use an anti-hypertensive agent, and amlodipine can certainly be used in this situation.
