Feline Hypoadrenocorticism (Addison's Disease)

Overview

Hypoadrenocorticism, commonly called Addison's disease, is a rare condition in cats involving insufficient production of adrenal hormones (cortisol and, often, aldosterone). It's notably even rarer in cats than Cushing's disease (its hormonal opposite), and its vague, waxing-and-waning symptoms make it a genuinely easy diagnosis to miss without specific testing.

Symptoms

• Vague, waxing-and-waning lethargy (moderate, common)
• Reduced appetite (moderate, common)
• Occasional vomiting (mild, uncommon)
• Collapse (crisis) (critical, rare)

Causes

Most commonly immune-mediated destruction of the adrenal glands; less commonly, damage from a tumor, infection, or other adrenal gland injury. Addison's disease results from inadequate production of essential adrenal hormones (cortisol and, importantly, aldosterone, which regulates sodium/potassium balance), and is genuinely rare in cats compared to dogs — when it does occur, it can follow destruction of adrenal tissue from various causes, or occasionally develops after abrupt discontinuation of long-term steroid medication without proper tapering.

Risk Factors

No strong established breed or sex predisposition in cats given the disease's rarity and limited case data relative to dogs, where it's much better characterized.

Transmission

Not applicable — not an infectious disease.

Incubation Period

Not applicable; develops gradually as adrenal hormone production declines.

Disease Stages & Progression

Often presents with vague, waxing-and-waning signs (lethargy, poor appetite, occasional vomiting) that can mimic several other more common conditions, sometimes progressing to a sudden, severe crisis (an Addisonian crisis) if enough adrenal function is lost.

Early Warning Signs

Vague, intermittent lethargy, reduced appetite, and occasional vomiting or weight loss — signs easily mistaken for many other, more common conditions.

Advanced Symptoms

In an acute Addisonian crisis: collapse, severe lethargy, dehydration, and dangerously abnormal electrolyte levels (particularly high potassium and low sodium) that can affect heart rhythm — this is a genuine emergency.

Diagnostic Methods

ACTH stimulation test is the gold-standard diagnostic test, checking whether the adrenal glands respond normally to stimulation. Bloodwork often shows a characteristic electrolyte pattern (low sodium, high potassium) that raises suspicion; an ACTH stimulation test, measuring how the adrenal glands respond to a stimulating hormone, provides definitive confirmation by showing an inadequately low cortisol response.

Veterinary Examination Process

General exam assessing hydration, heart rhythm (given the electrolyte effects), and overall condition.

Recommended Lab Tests

Electrolyte panel (sodium/potassium ratio), ACTH stimulation test.

Diagnostic Imaging

Not typically the primary diagnostic tool; used to rule out other causes of similar signs.

Blood Test Indicators

An abnormal sodium-to-potassium ratio on routine bloodwork is often the first clue prompting specific testing; the ACTH stimulation test is the definitive diagnostic test.

Biopsy / Histopathology

Not typically used for diagnosis.

Differential Diagnoses

Chronic kidney disease, gastrointestinal disease, and other causes of vague lethargy/appetite changes — the sodium/potassium ratio and ACTH stimulation test distinguish Addison's from these.

Home Monitoring Guidance

Watching for the return of vague lethargy/appetite signs in a diagnosed cat on hormone replacement, which can indicate the current dose needs adjustment.

Veterinary Treatment Options

Hormone replacement therapy (mineralocorticoid and/or glucocorticoid replacement, tailored to what the individual cat is deficient in) is the standard, generally effective long-term treatment; an acute crisis requires emergency stabilization (IV fluids, emergency medication) before longer-term hormone replacement is established. Hormone replacement (both a glucocorticoid for cortisol replacement and, when aldosterone is also deficient, a mineralocorticoid to manage sodium/potassium balance) forms lifelong treatment; an acute Addisonian crisis (severe weakness, collapse, dangerous electrolyte disturbance) is a genuine emergency requiring immediate IV fluids and hormone treatment.

Surgery Requirements

Not applicable.

Recovery Timeline

An acute crisis requires several days of hospitalization for stabilization; once on appropriate long-term hormone replacement, most cats do well, though the correct dose sometimes needs adjustment over the following weeks to months.

Possible Complications

An Addisonian crisis is the main serious complication risk, particularly if the underlying condition isn't yet diagnosed or treatment is interrupted.

Long-Term Management

Lifelong hormone replacement therapy with periodic monitoring and dose adjustment as needed.

Prevention

No known specific prevention given the immune-mediated mechanism believed to underlie most cases.

Vaccination Availability

Not applicable — not an infectious disease.

Prognosis

Good with appropriate lifelong hormone replacement therapy and monitoring, once correctly diagnosed.

References

American College of Veterinary Internal Medicine (ACVIM).

Medications Used

• Mineralocorticoid replacement (e.g., fludrocortisone or desoxycorticosterone pivalate)
• Glucocorticoid replacement (e.g., prednisolone) if needed
• Emergency IV fluids and medication during an acute crisis

Estimated Treatment Cost by Country

Frequently Asked Questions