What Is Addison's Disease in Cats?
Addison's disease, known medically as hypoadrenocorticism, is a condition in which the adrenal glands fail to produce sufficient quantities of their essential hormones — primarily cortisol (a glucocorticoid) and aldosterone (a mineralocorticoid). While the condition is well-recognised and relatively common in dogs, it is considerably rarer in cats. Nevertheless, feline Addison's disease is a serious, life-threatening disorder that requires prompt diagnosis and lifelong treatment. Because it is uncommon, it is sometimes missed or misdiagnosed, earning it the veterinary nickname "the great pretender."
The adrenal glands are small structures that sit adjacent to the kidneys. Their outer layer, the adrenal cortex, produces cortisol and aldosterone. Cortisol is vital for regulating metabolism, immune function, and the response to stress. Aldosterone controls the balance of sodium and potassium in the blood, which directly affects blood pressure and fluid balance. When the adrenal cortex is destroyed or severely damaged, the resulting hormone deficiency creates a systemic crisis.
How Common Is Addison's Disease in Cats?
Feline hypoadrenocorticism is genuinely uncommon. European veterinary literature estimates it accounts for a very small fraction of endocrine disorders seen in clinical practice. Cats of any age, breed, or sex can be affected, though there appears to be a slight predisposition in middle-aged female cats. Unlike in dogs, where certain breeds such as Standard Poodles, Portuguese Water Dogs, and Great Danes have a clear genetic predisposition, no strong breed predisposition has been established in cats.
Because of its rarity, cats with Addison's disease are often referred to specialist internal medicine services at university veterinary hospitals or specialist referral centres across the EU. If your veterinarian suspects this condition, seeking specialist input is advisable and appropriate.
Causes of Feline Addison's Disease
There are several potential causes of hypoadrenocorticism in cats.
Immune-Mediated Destruction
The most common naturally occurring cause is thought to be immune-mediated, where the body's own immune system mistakenly attacks and destroys the adrenal cortex over time. This results in progressive failure of cortisol and aldosterone production. The mechanism is analogous to that seen in autoimmune Addison's disease in humans and dogs.
Iatrogenic Addison's Disease
Iatrogenic (treatment-induced) hypoadrenocorticism is particularly relevant in cats and is arguably more frequently encountered in feline practice than the naturally occurring form. It occurs when cats who have been receiving long-term corticosteroid therapy for conditions such as inflammatory bowel disease, asthma, or immune-mediated skin disease have their medication abruptly discontinued or reduced too quickly. The exogenous steroids suppress the normal functioning of the hypothalamic-pituitary-adrenal axis, and the adrenal glands atrophy from disuse. Without a gradual, supervised taper, the glands cannot mount an adequate response and an Addisonian crisis may follow.
Other Causes
Less commonly, the adrenal cortex may be damaged by granulomatous disease, infiltrative tumours, haemorrhage, or infarction. Trilostane or mitotane therapy used to treat Cushing's disease can also, if over-dosed, produce iatrogenic Addison's disease.
Symptoms of Addison's Disease in Cats
The clinical signs of feline hypoadrenocorticism are often vague, non-specific, and wax and wane over time, which contributes to delayed diagnosis. Common symptoms include:
- Lethargy, weakness, and generalised depression
- Decreased appetite or complete anorexia
- Vomiting and diarrhoea
- Weight loss
- Dehydration despite normal or reduced water intake
- Muscle weakness or reluctance to move
- Bradycardia (abnormally slow heart rate), which distinguishes this condition from many other causes of collapse
- Shaking or trembling
- Collapse in advanced or acute presentations
The episodic nature of the symptoms — often improving temporarily with supportive care such as intravenous fluids, only to return — is a characteristic pattern that should raise suspicion for this condition.
The Addisonian Crisis: A Veterinary Emergency
An Addisonian crisis is an acute, life-threatening decompensation that can occur when a cat with Addison's disease is subjected to a significant physical or emotional stressor, or when the disease has progressed to a point where the hormonal deficit can no longer be compensated. It may also occur in previously undiagnosed cats following steroid withdrawal.
Signs of an Addisonian crisis include severe collapse, profound weakness, marked bradycardia, hypotension (dangerously low blood pressure), hypothermia, and shock. Blood tests will typically show dangerous elevations in potassium (hyperkalaemia) and drops in sodium (hyponatraemia). The sodium-to-potassium ratio below 27 is a classic finding that strongly supports a diagnosis of hypoadrenocorticism.
An Addisonian crisis requires immediate emergency treatment with intravenous fluids, injectable glucocorticoids (such as hydrocortisone or dexamethasone), and close cardiac monitoring. Without rapid intervention, the condition can be fatal. If you believe your cat is in acute distress, contact your vet or an emergency veterinary clinic without delay.
Diagnosis of Feline Hypoadrenocorticism
Diagnosis begins with a thorough clinical history and physical examination. Routine blood tests may reveal the classic electrolyte abnormalities (low sodium, high potassium), elevated kidney markers, and low blood glucose. An electrocardiogram (ECG) may show abnormalities consistent with hyperkalaemia.
The definitive diagnostic test is the ACTH stimulation test. A baseline blood cortisol level is measured, synthetic ACTH is administered, and a second cortisol measurement is taken one hour later. In a cat with hypoadrenocorticism, baseline cortisol is low and there is minimal or no rise in response to ACTH stimulation, indicating that the adrenal gland cannot respond normally. This is distinct from the exaggerated response seen in Cushing's disease.
Abdominal ultrasound may reveal small, atrophied adrenal glands in naturally occurring Addison's disease. EU specialist referral is strongly recommended to ensure accurate interpretation of results and optimal treatment planning.
Treatment: Glucocorticoid and Mineralocorticoid Replacement
Treatment of feline Addison's disease involves replacing the hormones the adrenal glands can no longer produce. Unlike in dogs, where a combination of glucocorticoid and mineralocorticoid supplementation is the standard approach, some cats with naturally occurring hypoadrenocorticism have only glucocorticoid deficiency (atypical Addison's disease). In these cases, only glucocorticoid replacement is required initially, though mineralocorticoid replacement may become necessary over time.
Glucocorticoid Replacement
Prednisolone is the most commonly used oral glucocorticoid in cats. The dose is kept as low as possible while maintaining clinical stability, and it must be increased during periods of stress, illness, or surgery — a concept known as "stress dosing." Owners must never abruptly stop this medication.
Mineralocorticoid Replacement
Fludrocortisone acetate (Florinef) is an oral mineralocorticoid used in cats requiring aldosterone replacement. Alternatively, desoxycorticosterone pivalate (DOCP) can be administered as an injection every 25 to 30 days, which some owners find more convenient. Regular monitoring of electrolytes is essential to ensure the dose is appropriate.
Long-Term Management and Quality of Life
With correct and consistent treatment, cats with Addison's disease can lead full, comfortable lives. Key aspects of long-term management include:
- Regular blood tests (sodium, potassium, kidney values) every three to six months
- Keeping a supply of emergency oral prednisolone at home and knowing when to administer it
- Informing any treating vet — including out-of-hours emergency services — of the diagnosis
- Minimising unnecessary stressors in the cat's environment
- Following veterinary advice regarding dose adjustments during illness
Cats managed through specialist internal medicine services at EU referral centres typically have better outcomes due to tailored monitoring protocols. Ensuring your cat receives a high-quality, easily digestible diet also supports overall health. Zooplus offers a wide range of premium wet cat foods and veterinary diet options suitable for cats with chronic health conditions.
Feline Addison's disease may be rare, but it is entirely manageable with the right veterinary partnership and owner commitment. Early recognition and specialist involvement can be lifesaving.