Cat Hyperaldosteronism (Conn's Syndrome): Signs to Watch

Feline hyperaldosteronism — also called Conn's syndrome — is a condition where one or both adrenal glands overproduce the hormone aldosterone, causing dangerous potassium loss, high blood pressure, and muscle weakness. It is one of the most commonly missed causes of sudden-onset paralysis in older cats.

Last reviewed: June 2026

What Is Hyperaldosteronism and Why Does It Harm Cats?

Hyperaldosteronism occurs when the adrenal glands secrete excess aldosterone, which drives the kidneys to retain sodium while excreting potassium and, to a lesser extent, hydrogen ions. The resulting hypokalemia disrupts the electrical gradients muscles depend on, and the concurrent systemic hypertension can silently damage the eyes, kidneys, heart, and brain before any owner notices a problem. As described in Ettinger's Textbook of Veterinary Internal Medicine, primary hyperaldosteronism in cats most often arises from a unilateral adrenal adenoma (benign tumor), though bilateral adrenal hyperplasia and, less commonly, adrenal carcinoma also occur. Most affected cats are middle-aged to older, typically over seven years, and the condition is likely underdiagnosed because its early signs — mild lethargy and reduced jumping — overlap with normal aging.

Key Signs to Recognize

The clinical picture of feline hyperaldosteronism is shaped by two parallel processes: profound muscle weakness from potassium depletion, and end-organ damage from hypertension.

Neuromuscular signs (most distinctive):

• Cervical ventroflexion — the neck drops forward and the cat cannot hold its head up
• Hindlimb weakness or collapse, often appearing suddenly
• Plantigrade stance — the cat walks on the back of the hocks rather than the toes
• Generalized weakness, staggering gait

Hypertension-related signs:

• Sudden blindness, dilated pupils that do not respond to light, or visible blood in the eye (hypertensive retinopathy or retinal detachment)
• Disorientation or seizures from hypertensive encephalopathy
• Increased thirst and urination
• Unexplained weight loss

General signs:

• Progressive lethargy
• Reduced appetite
• Dull, unkempt coat

A hallmark pattern is an older cat that abruptly cannot hold its head up or collapses in the hindlimbs — this combination of cervical ventroflexion and acute weakness should prompt immediate suspicion of hypokalemia, which is the biochemical signature of hyperaldosteronism.

How Vets Diagnose Conn's Syndrome in Cats

Diagnosis rests on finding elevated aldosterone alongside suppressed or low renin activity, combined with compatible clinical findings.

Djajadiningrat-Laanen et al., 2011, JFMS described the diagnostic approach to primary hyperaldosteronism in cats, confirming that serum aldosterone measurement combined with blood pressure evaluation and adrenal imaging constitute the essential diagnostic triad.

Diagnostic workup typically includes:

1. Serum biochemistry — hypokalemia (potassium often <3.5 mEq/L, sometimes <2.5) is the most consistent finding; sodium may be in the high-normal range
2. Blood pressure measurement — systolic pressure ≥160 mmHg on repeated measurement supports hypertension; ≥180 mmHg is severe
3. Serum aldosterone — elevated, often markedly so
4. Plasma renin activity or aldosterone:renin ratio — a high ratio (elevated aldosterone with suppressed renin) confirms primary adrenal disease
5. Adrenal imaging — abdominal ultrasound or CT identifies a unilateral mass in many cases; bilateral enlargement suggests hyperplasia

Treatment Options and What to Expect

Management depends on whether the cause is a surgically removable tumor or diffuse hyperplasia.

Medical management (all cases initially):

• Oral potassium supplementation to correct hypokalemia — potassium gluconate is preferred; improvement in muscle strength is often seen within days
• Blood pressure control with amlodipine, the first-line antihypertensive in cats
• Aldosterone antagonist spironolactone helps both blood pressure and potassium retention

Surgical management (unilateral adenoma):

• Adrenalectomy is curative in cats with a single adenoma — potassium normalizes and hypertension often resolves post-operatively
• Cats with bilateral disease are managed medically long-term

As described in Ramsey's BSAVA Manual of Small Animal Endocrinology, cats managed surgically for unilateral adrenal adenoma generally have a good prognosis. Regular monitoring of blood pressure and potassium is essential for all affected cats; the AAFP Senior Care Guidelines, 2021 recommend systematic blood pressure measurement in cats over seven years as part of routine senior care — the age at which most hyperaldosteronism cases are first detected.

When to See a Vet

Call your vet today if:

• Your cat is walking with weak, wobbly hindlimbs or seems to drag the back legs
• Your cat holds its neck low or cannot lift its head normally
• Your cat is unusually lethargic and not interested in food or play
• Your cat is drinking and urinating noticeably more than usual
• Your cat has unexplained weight loss over the past few weeks

Go to the ER immediately if:

• Your cat suddenly cannot stand, collapses, or cannot support the hindquarters at all
• Your cat has a seizure or appears disoriented and unaware of surroundings
• Your cat's pupils are fixed and dilated or there is visible blood in the eye
• Your cat appears to have lost vision suddenly — bumping into objects, not tracking movement

Frequently Asked Questions

What are the first signs of hyperaldosteronism in cats? Early signs are often subtle — mild hindlimb weakness, reduced willingness to jump, and slightly increased thirst. The most alarming presentation is sudden-onset cervical ventroflexion (neck drooping) or hindlimb collapse, which reflects severe potassium depletion. Many cats are also found to have high blood pressure discovered during a routine senior exam before dramatic signs appear.

Can cats recover from Conn's syndrome? Yes, with appropriate treatment many cats recover well. Cats with a surgically removable adrenal adenoma often return to normal potassium levels and blood pressure after adrenalectomy. Cats managed medically can remain stable for months to years on potassium supplementation and amlodipine, though regular monitoring is essential to catch potassium drops or blood pressure spikes early.

Is hyperaldosteronism painful for cats? The muscle weakness from hypokalemia itself is not typically painful, but severe low potassium can cause muscle cramps and profound weakness that distresses cats. Hypertensive retinal detachment and sudden blindness can cause significant disorientation. Prompt treatment to normalize potassium usually produces visible improvement in comfort and mobility within days.

How much does diagnosing and treating hyperaldosteronism cost? Initial workup — exam, chemistry panel, blood pressure, and abdominal ultrasound — commonly runs $400–800. Aldosterone and renin testing can add $150–300. Adrenalectomy, when indicated, typically costs $2,000–4,500 including pre-operative bloodwork and hospitalization. Long-term medical management (potassium supplements and amlodipine) runs approximately $40–80 per month in drug costs, plus quarterly monitoring visits.

How common is hyperaldosteronism in cats? Primary hyperaldosteronism is increasingly recognized as a significant cause of hypertension and hypokalemia in older cats, though it remains underdiagnosed. As awareness grows among veterinarians and routine blood pressure screening expands in senior cats, more cases are being identified before dramatic muscle weakness develops.

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