Feline hyperaldosteronism (primary hyperaldosteronism, Conn's syndrome) is an increasingly recognized endocrine disease in older cats caused by excess aldosterone secretion from one or both adrenal glands, leading to severe hypokalemia, muscle weakness, and hypertension.
The condition is often misdiagnosed as idiopathic hypertension or CKD because its hallmark signs — neck ventroflexion and hind-end weakness — mimic neuromuscular disease.
Last reviewed: June 2026
What Is Feline Hyperaldosteronism?
Primary hyperaldosteronism in cats occurs when an adrenal gland tumor (adenoma or carcinoma) or bilateral adrenal hyperplasia autonomously secretes excess aldosterone independent of the renin-angiotensin-aldosterone system (RAAS). Aldosterone normally promotes sodium retention and potassium excretion by the kidney; excess aldosterone drives severe urinary potassium wasting (hypokalemia), sodium retention (contributing to hypertension), and secondarily suppresses renin. As described in Ettinger's Textbook of Veterinary Internal Medicine, feline primary hyperaldosteronism was once thought rare but is now considered a significant cause of hypertension and hypokalemia in older cats, likely underdiagnosed due to low clinical awareness.
Middle-aged to older cats (typically 8–16 years) are most commonly affected. Unlike the classic Conn's syndrome presentation in humans (hypertension without hypokalemia in mild cases), cats with hyperaldosteronism almost universally present with clinically significant hypokalemia. This severe potassium depletion damages skeletal muscle and can — if untreated — lead to acute rhabdomyolysis or cardiac arrhythmias.
Clinical Signs: Weakness Is the Red Flag
The most distinctive clinical sign is generalized muscle weakness with cervical ventroflexion — the cat cannot hold its head up and the neck droops when walking. This may be mistaken for neurological disease. Other signs include: hindlimb weakness or stiffness, reluctance to jump, an abnormal plantigrade posture, lethargy, weight loss, and polydipsia/polyuria (if concurrent CKD or diabetes is present). Some cats are incidentally found to have severe hypertension on routine blood pressure screening, prompting endocrine workup.
Hypertensive retinopathy can occur — sudden onset of apparent blindness or dilated non-responsive pupils should prompt immediate blood pressure measurement. Serum potassium in affected cats is often severely low (below 3.0 mEq/L, sometimes below 2.5 mEq/L), and this degree of hypokalemia causes the muscle signs. As noted in the AAFP Senior Care Guidelines, 2021, routine blood pressure and serum electrolyte monitoring at senior wellness visits is a critical tool for catching diseases like hyperaldosteronism before they reach crisis severity.
Diagnosis
Diagnosis begins with the clinical presentation (severe hypokalemia + hypertension + weakness in an older cat) and blood pressure measurement (systolic typically 160–240 mmHg). The next step is measuring plasma aldosterone concentration (PAC) and plasma renin activity (PRA) — a markedly elevated PAC with suppressed PRA (aldosterone-to-renin ratio strongly elevated) is the biochemical fingerprint of primary hyperaldosteronism. This testing requires specific sample handling (chilled, prompt submission) and specialized laboratory processing.
Adrenal imaging with ultrasound or CT scan is then performed to identify whether the cause is a unilateral tumor (adenoma or carcinoma — more common, potentially curable with surgery) or bilateral hyperplasia (treated medically). Unilateral adrenal adenomas appear as well-defined hypoechoic masses on ultrasound. CT is more sensitive for small lesions and better characterizes malignant features (vascular invasion, local extension). Full diagnostic workup including hormonal assays and advanced imaging typically costs $1,000–2,500.
Treatment
For unilateral adrenal tumors, adrenalectomy (surgical removal of the affected gland) is potentially curative. Potassium supplementation and spironolactone (an aldosterone antagonist) are used to stabilize the cat before surgery. Spironolactone blocks aldosterone receptors in the kidney, restoring normal potassium balance, and typically brings serum potassium back toward normal within days to weeks. Blood pressure is managed with amlodipine (the preferred antihypertensive in cats).
Medical management (spironolactone + amlodipine + potassium supplementation) is used for cats that are poor surgical candidates or have bilateral hyperplasia. This approach controls signs but does not address the underlying tumor. Median survival with medical management is reported at 17–21 months from diagnosis, while surgically cured cats (with benign adenomas) may live normal lifespans. As described in Ramsey's BSAVA Manual of Small Animal Endocrinology, meticulous potassium monitoring during initial treatment is essential to prevent rebound hyperkalemia during aggressive supplementation.
Monthly medications (spironolactone + amlodipine + potassium) cost $50–120. Adrenalectomy at a surgical referral center costs $3,000–6,000 including hospitalization. Regular monitoring rechecks run $150–350 every 1–3 months.
When to See a Vet
Call your vet today if:
- Your senior cat cannot hold its head up (cervical ventroflexion)
- Sudden hind-end weakness, difficulty jumping, or abnormal gait
- Polydipsia/polyuria with lethargy in a cat over 8 years old
- Blood pressure above 160 mmHg found at routine wellness visit
Go to the ER immediately if:
- Sudden blindness or fixed dilated pupils (hypertensive emergency)
- Collapse or inability to walk
- Severe weakness with neck drooping acutely
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Frequently Asked Questions
Is feline hyperaldosteronism the same as Addison's disease? No — they are opposite conditions. Hyperaldosteronism involves excess aldosterone production (from a tumor), causing low potassium and high blood pressure. Addison's disease (hypoadrenocorticism) involves insufficient aldosterone and cortisol, causing high potassium and low blood pressure. Both are adrenal disorders but are treated very differently.
What makes hyperaldosteronism hard to diagnose in cats? The cardinal signs — weakness and hypertension — are attributed to more common conditions like CKD or idiopathic hypertension in older cats. Hypokalemia on routine bloodwork may be attributed to inappetence or vomiting without further investigation. Specific aldosterone and renin testing plus adrenal imaging is required for diagnosis and is not performed routinely at wellness visits.
How much does hyperaldosteronism treatment cost in cats? Medical management (spironolactone, amlodipine, potassium) costs $50–120/month plus $150–350 per monitoring visit every 1–3 months. Adrenalectomy costs $3,000–6,000 at a surgical referral center. Long-term medical management over 1–2 years typically costs $2,000–5,000 in medications and monitoring combined.
Can a cat with hyperaldosteronism recover fully? Cats with surgically resectable adrenal adenomas have the best prognosis — many experience resolution of hypokalemia and hypertension following adrenalectomy and can live normal lifespans. Cats managed medically or with bilateral hyperplasia have median survivals of 17–21 months with good quality of life.
Should all senior cats be screened for hyperaldosteronism? Annual blood pressure measurement and serum electrolytes are recommended at senior wellness visits (cats over 7 years). Unexplained hypokalemia (low potassium below 3.5 mEq/L) or persistent hypertension above 160 mmHg not fully explained by CKD or hyperthyroidism warrants aldosterone and renin testing.
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