CONDITION

Hyperaldosteronism in Cats

Hyperaldosteronism in cats describes a pattern in which the adrenal glands produce too much of a hormone called aldosterone. Aldosterone helps regulate the balance of sodium and potassium in the blood, and when present in excess, it tends to drive potassium levels down and blood pressure up. The condition arises most often from a small tumour in one or both adrenal glands, though in some cats the cause remains unclear. Owners may notice increased thirst and urination, occasional weakness or a stiff, stilted gait, or sometimes no outward signs at all—the pattern may only come to light during blood tests taken for other reasons. Muscle weakness, when present, often reflects the low potassium levels that result from aldosterone's effects on the kidneys. Some cats show high blood pressure on routine screening, which may prompt further investigation. This page explores the signals that may suggest hyperaldosteronism, what is happening inside the body to produce those signals, how the condition is investigated through blood tests and imaging, and the approaches that exist for managing it over time. The goal is to help you understand the shape of the condition and the conversations that may follow.

Why this matters now

Hyperaldosteronism in cats tends to appear in middle-aged to older animals, typically between eight and fifteen years of age, though younger cats can occasionally be affected. No strong breed predisposition has been identified, and the condition arises equally in males and females. In many cases, the underlying adrenal abnormality develops quietly over months or years before signs become apparent.

The condition often progresses slowly, with potassium levels falling gradually as aldosterone production rises. Some cats show subtle signs early on—mild muscle weakness or increased thirst—that may come and go or worsen incrementally. In other cats, the pattern remains silent until blood pressure rises to a level that prompts concern, or until routine blood work reveals markedly low potassium. The rate of progression varies considerably between individuals, and the trajectory can be influenced by whether one or both adrenal glands are involved.

Signals & patterns

Early signals

Increased thirst and urination

Many cats begin drinking more water than usual and producing larger volumes of urine. This happens because low potassium levels can interfere with the kidneys' ability to concentrate urine, prompting the body to compensate by taking in more fluid.

Intermittent muscle weakness

Some owners notice their cat seems slightly less steady on their feet, or occasionally sits in an unusual posture with the hind legs splayed. The weakness may be subtle at first and can come and go, reflecting fluctuations in potassium levels that affect normal muscle contraction.

Weight loss despite normal appetite

A cat may continue to eat well but lose body condition slowly over weeks or months. The metabolic effects of chronic potassium depletion and the energy cost of compensating for electrolyte imbalance can contribute to gradual weight loss.

Occasional neck ventroflexion

In some cats, the head and neck begin to droop forward, particularly when the animal is walking or standing. This posture reflects weakness in the muscles that normally hold the head upright, and tends to appear when potassium levels are markedly low.

Later signals

Persistent stilted gait

As potassium depletion continues, the hind limbs may appear stiff and the cat may walk with a shuffling or plantigrade stance, placing the hocks on the ground rather than walking on the toes. This reflects more severe muscle weakness and can make jumping or climbing difficult.

Vision changes or eye abnormalities

High blood pressure sustained over time can damage the small blood vessels in the retina, occasionally leading to sudden blindness or visible changes in the appearance of the eye. Owners may notice dilated pupils, blood within the eye, or a cat that seems disoriented or reluctant to move in dim light.

Reduced activity and reluctance to move

Cats with advanced muscle weakness may spend more time resting and show less interest in play, grooming, or exploration. The effort required to move with weakened muscles can make previously routine activities uncomfortable or exhausting.

Click to read about the biological mechanisms

How this is usually investigated

Investigation typically begins with a review of the cat's history and a physical examination, followed by blood tests to measure electrolyte levels and kidney function. When low potassium or unexplained high blood pressure appears, further tests may be arranged to measure aldosterone and related hormones directly. Imaging of the adrenal glands can help determine whether a discrete mass is present and, if so, whether one or both glands are involved.

Blood biochemistry

Purpose: This test measures potassium, sodium, and other electrolytes in the blood, and often reveals the characteristic low potassium that prompts suspicion of hyperaldosteronism. It can also show changes in kidney function that may accompany the condition.
Considerations: Potassium levels can fluctuate, and some cats with hyperaldosteronism may have normal or only mildly low potassium on a single sample. The result is most useful when combined with other findings rather than interpreted in isolation.

Blood pressure measurement

Purpose: This involves placing a cuff around the cat's leg or tail to assess whether blood pressure is elevated, which occurs in many cats with hyperaldosteronism. Serial measurements can help establish a pattern and reduce the influence of stress or movement.
Considerations: Blood pressure can rise temporarily in a clinical setting, and several readings are often needed to distinguish sustained high pressure from transient elevations. Not all cats with hyperaldosteronism show high blood pressure at every visit.

Aldosterone and renin measurement

Purpose: A blood sample is analysed to measure the levels of aldosterone and, often, renin—a hormone that normally regulates aldosterone release. In hyperaldosteronism, aldosterone tends to be high whilst renin remains low, a pattern that helps distinguish this condition from other causes of electrolyte disturbance.
Considerations: The ratio of aldosterone to renin can be influenced by medications, diet, and the cat's hydration status, so careful preparation and interpretation are needed. Some laboratories require samples to be handled in specific ways to preserve hormone stability.

Abdominal ultrasonography

Purpose: Ultrasound imaging allows visualisation of the adrenal glands and can identify small masses or enlargement of one or both glands. It can also reveal changes in other abdominal organs, such as the kidneys, that may be relevant to the overall picture.
Considerations: The adrenal glands are small and can be challenging to see clearly, particularly in cats with little body fat or those who are restless during the examination. A normal ultrasound does not entirely rule out hyperaldosteronism, as some tumours are too small to detect or the change may be diffuse rather than mass-forming.

Computed tomography or magnetic resonance imaging

Purpose: Cross-sectional imaging provides detailed views of the adrenal glands and surrounding structures, and can identify very small masses that may be missed on ultrasound. It is particularly useful when surgery is being considered, as it helps map the anatomy and assess whether other organs are involved.
Considerations: These techniques require general anaesthesia and access to specialist imaging facilities, which may not be available in all locations. The additional detail can be helpful in planning treatment, though it does not change the underlying diagnosis in most cases.

Options & trade-offs

Management of hyperaldosteronism is typically tailored to the individual cat and the findings on investigation. Approaches range from medication to reduce aldosterone's effects or replace lost potassium, through to surgery to remove an affected adrenal gland when a single mass is identified. Many cats are managed with a combination of methods, and the balance between them can shift over time as the condition evolves or as the cat's tolerance for different interventions becomes clearer.

Potassium supplementation

Oral potassium supplements can be given to raise blood potassium levels and help resolve muscle weakness or other signs linked to low potassium. The dose is adjusted based on regular blood tests, and the supplement is typically given once or twice daily, often mixed with food. Some formulations are more palatable than others, and finding one the cat will accept can take trial.

Trade-offs: Potassium supplementation addresses the consequence of aldosterone excess rather than the excess itself, so aldosterone levels and blood pressure may remain high even when potassium normalises. Some cats find the taste unpleasant, and gastrointestinal upset can occur if doses are too high or given on an empty stomach.

Aldosterone-blocking medication

Drugs such as spironolactone work by blocking the receptors aldosterone uses in the kidneys, reducing the loss of potassium and helping to lower blood pressure. The medication is given daily, and blood tests are repeated periodically to monitor potassium, kidney function, and sometimes blood pressure. Over time, the dose may be adjusted to find the lowest effective level.

Trade-offs: Spironolactone does not reduce aldosterone production itself, so the underlying adrenal abnormality persists. Some cats experience mild digestive upset or increased urination, and the medication may interact with other drugs or require careful use in cats with existing kidney concerns.

Blood pressure medication

Drugs such as amlodipine can be used to lower blood pressure when it remains elevated despite other measures. The medication is given daily, and blood pressure is monitored to assess response and guide dose adjustments. It is often used alongside potassium supplementation or aldosterone-blocking drugs rather than as a sole treatment.

Trade-offs: Blood pressure medication does not address the hormonal imbalance or the low potassium directly, so it is typically part of a broader approach. Doses that lower pressure too far can cause lethargy or weakness, and some cats may not tolerate the medication well.

Surgical removal of the affected adrenal gland

When a single adrenal mass is identified and the cat is otherwise healthy enough for surgery, the affected gland can be removed. The procedure requires general anaesthesia and is typically carried out by a specialist surgeon, as the adrenal glands sit close to major blood vessels and the kidneys. If successful, aldosterone levels can fall to normal and signs may resolve, though some cats require potassium supplementation temporarily after surgery whilst the remaining gland adjusts.

Trade-offs: Surgery carries the risks inherent in any general anaesthetic and abdominal operation, and is less straightforward when both glands are abnormal or when other health concerns complicate recovery. Not all cats are suitable candidates, and imaging beforehand cannot always predict whether the mass can be fully removed or whether other changes are present.

Monitoring without active intervention

In some cats, particularly those with mild biochemical changes and no outward signs, periodic monitoring of blood pressure, potassium, and general wellbeing may be an option. Blood tests and pressure checks are repeated at intervals to watch for progression, and treatment can be introduced if signs develop or parameters shift beyond agreed thresholds.

Trade-offs: This approach avoids the cost and practical demands of medication or surgery, but it does not slow the underlying process or protect against the gradual effects of high aldosterone. Some cats may progress to a point where intervention becomes more complex or less effective than it might have been earlier.

Common misconceptions

Misconception:

"A cat with hyperaldosteronism will always show obvious muscle weakness or collapse."

Reality:

Many cats with hyperaldosteronism show no outward signs at all, and the condition may only be detected through blood tests taken for other reasons. Muscle weakness, when it occurs, tends to be intermittent or subtle—a stiff gait or reluctance to jump—rather than dramatic collapse, and some cats maintain normal movement even when potassium levels are quite low.

Misconception:

"Once a cat starts medication for hyperaldosteronism, the dose will stay the same indefinitely."

Reality:

The dose of potassium supplements or aldosterone-blocking drugs often needs adjustment over time as the cat's response becomes clear or as the underlying condition evolves. Blood tests are repeated periodically to guide these changes, and what works well in the first months may need rethinking later if potassium drifts out of range or blood pressure shifts.

Misconception:

"Surgery to remove an adrenal tumour will always cure hyperaldosteronism completely."

Reality:

Whilst surgery can resolve the hormonal imbalance in many cats with a single adrenal mass, some cats have abnormalities in both glands or develop recurrence over time. The success of surgery also depends on whether the mass can be fully removed without complication, and some cats may still require medication afterwards to manage blood pressure or support the remaining gland as it adjusts.

Related conditions

Systemic Hypertension in Cats

Systemic hypertension in cats often arises as a consequence of hyperaldosteronism, because excess aldosterone tends to drive blood pressure upward through its effects on sodium retention and blood vessel tone. Cats with hyperaldosteronism are typically screened for high blood pressure, and those found to have hypertension may be investigated for aldosterone excess as a possible underlying cause.

Phaeochromocytoma

Phaeochromocytoma is another tumour of the adrenal gland that produces excessive hormones, though in this case adrenaline and related compounds rather than aldosterone. Both conditions share the feature of adrenal hormone excess and can present with elevated blood pressure, though the wider pattern of signs and the hormones involved differ.

Acute Kidney Injury

Acute kidney injury can develop in cats with hyperaldosteronism if severe hypokalaemia—low potassium—persists, because prolonged potassium depletion may damage kidney tissue. Conversely, investigation of kidney disease sometimes uncovers electrolyte disturbances that prompt testing for hyperaldosteronism.

Adrenal Tumours

Hyperaldosteronism in cats most often arises from a tumour in one or both adrenal glands, making adrenal tumours the direct anatomical substrate of the condition in many cases. Imaging that identifies an adrenal mass in a cat with appropriate blood changes often forms part of the diagnostic picture for hyperaldosteronism.

Cushings Disease in Cats

Cushing's disease is another uncommon endocrine condition in cats involving excessive hormone production—in this case cortisol rather than aldosterone—and it can occasionally arise from adrenal tumours. Both conditions belong to a broader family of adrenal hormone excess states and may enter the differential when investigating signs such as increased thirst or abnormal blood tests, though the patterns they produce differ.

Understanding the shape of hyperaldosteronism can open conversations about how monitoring and management might fit into your cat's routine, and how different approaches balance practical demands with the pattern you are seeing. The condition sits within a broader picture of metabolic and hormonal health in older cats, and it may be useful to consider how blood pressure, kidney function, and electrolyte balance interact over time. Other content in the metabolic health section explores related patterns that can influence or coexist with hyperaldosteronism, and may offer additional context for the conversations ahead.