Serious severity
Hyperaldosteronism (Conn's Syndrome)
An adrenal tumour floods the body with aldosterone, driving potassium down and blood pressure up. Sudden blindness or a drooping neck are often the first clue.
⚠️ Common symptoms
Aldosterone is the body's salt-retaining hormone. Released by the outer layer of the adrenal gland, it tells the kidney to hold on to sodium and to let potassium go — a system designed to defend blood volume in an animal that is losing fluid. Set that system running continuously, with a tumour issuing the instruction regardless of need, and two things follow inevitably. Sodium and water retention push blood pressure up. Potassium is dumped into the urine until the cat becomes profoundly deficient.
Each of those has a signature. Severe hypokalaemia produces a very characteristic weakness, most striking in the muscles of the neck: a cat that cannot hold its head up, standing with the chin pressed towards the chest, watching the world from an oddly low angle. It is an alarming sight, and it is largely reversible with potassium replacement. Sustained hypertension attacks the eye, where the small vessels of the retina bleed or leak until the retina lifts away from the back of the eye. Owners often describe a cat that was fine yesterday walking into furniture this morning with hugely dilated pupils.
For a long time this condition was considered rare in cats. It is now better described as under-recognised. Older cats commonly have chronic kidney disease, and both low potassium and high blood pressure occur in kidney disease too, so it is easy for the real driver to be missed. The clue is severity and disproportion — a potassium that stays low despite generous supplementation, or a blood pressure that will not settle on standard doses, in a cat whose kidney values do not seem bad enough to explain either.
Confirming it takes a measured blood aldosterone alongside plasma renin activity, plus imaging. Abdominal ultrasound in experienced hands will often show a nodule on one adrenal gland, and CT gives a clearer picture of the gland's relationship to the vena cava, which matters enormously if surgery is being considered.
The prognosis divides sharply. A cat whose tumour is removed surgically may be cured outright and live for years with no ongoing medication. A cat managed medically can still do well, sometimes for a long time, but is being controlled rather than fixed. And a cat whose retinas detached before diagnosis is very often permanently blind, which is survivable — blind cats adapt remarkably well in a stable home — but avoidable. That gap between avoidable and permanent is the entire argument for measuring blood pressure in older cats as a matter of routine.
🔍 Causes
The adrenal glands normally release aldosterone in carefully regulated amounts to manage sodium and potassium balance. In primary hyperaldosteronism a functional adrenal tumour — an adenoma or an adenocarcinoma — produces it without regard to the body's needs. The result is relentless sodium retention and potassium loss through the kidneys. Less commonly, both adrenal glands undergo a non-tumorous overgrowth called bilateral nodular hyperplasia with the same effect. It is a disease of older cats, typically over ten, with no strong breed or sex predisposition, and it is now recognised as a genuinely under-diagnosed cause of high blood pressure in the elderly cat.
🛡 Prevention
There is no way to prevent an adrenal tumour. What can be prevented is the catastrophic outcome, and that means catching the disease before the retinas detach. Annual — and from twelve years, twice-yearly — health checks that include blood pressure measurement and a biochemistry panel with potassium are the practical answer. A persistently low potassium in an older cat should never be shrugged off as incidental, and a high blood pressure without an obvious cause deserves an aldosterone measurement rather than an assumption of idiopathic hypertension.
💊 Treatment
Emergency stabilisation comes first: potassium supplementation, given intravenously in a severely weak cat and orally thereafter, and blood pressure control with amlodipine. Spironolactone, which blocks aldosterone's effect on the kidney, is the mainstay of medical management and often allows potassium supplementation to be reduced. For cats with a single adrenal tumour and no evidence of spread, surgical removal of the affected gland is potentially curative and is the treatment of choice where an experienced surgical team is available — it is technically demanding surgery, given the gland's proximity to major blood vessels, but outcomes in well-selected cats are genuinely good, with many living for years afterwards. Cats with bilateral adrenal enlargement, spread to other organs, or significant concurrent kidney disease are usually managed medically instead, which controls signs well but does not cure.
🎬 Related videos
⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.