Feline Hypoadrenocorticism (Addison's Disease): Diagnosis and Management

Feline hypoadrenocorticism, also known as Addison's disease, is an uncommon endocrine disorder in cats characterized by deficient production of glucocorticoids, mineralocorticoids, or both from the adrenal cortex. This condition results from primary adrenal gland destruction or, less commonly, secondary pituitary dysfunction. Veterinarians must recognize that feline hypoadrenocorticism presents differently from the canine form, with more subtle clinical signs and a lower index of suspicion required for diagnosis. This article provides a detailed guide to pathophysiology, clinical recognition, diagnostic testing, and long-term management of feline Addison's disease, drawing on current evidence and clinical guidelines.

At a Glance

Pathophysiology and Etiology

Primary Hypoadrenocorticism

Primary hypoadrenocorticism results from destruction of the adrenal cortex, leading to deficiency of both glucocorticoids (cortisol) and mineralocorticoids (aldosterone). In dogs, immune-mediated destruction is the most common cause, but in cats, the etiology is less well characterized. A 2024 update on feline hypoadrenocorticism noted that primary disease appears more common than secondary in cats, though the underlying cause often remains unidentified (Hypoadrenocorticism in cats: a 40-year update, Journal of Feline Medicine and Surgery, 2024, PubMed). Potential causes include immune-mediated adrenalitis, neoplasia, infection (e.g., fungal disease), or iatrogenic causes such as mitotane or trilostane administration.

Secondary Hypoadrenocorticism

Secondary hypoadrenocorticism arises from deficient pituitary adrenocorticotropic hormone (ACTH) secretion, resulting in isolated glucocorticoid deficiency. Mineralocorticoid production is preserved because aldosterone secretion is primarily regulated by the renin-angiotensin-aldosterone system (RAAS), not ACTH. Causes include pituitary neoplasia, head trauma, or exogenous glucocorticoid administration leading to suppression of the hypothalamic-pituitary-adrenal (HPA) axis. A review of pituitary deficiencies in companion animals noted that secondary hypoadrenocorticism is less common than primary disease (Pituitary deficiencies, Topics in Companion Animal Medicine, 2012, PubMed).

Aldosterone Deficiency and Electrolyte Disturbances

Aldosterone deficiency impairs renal potassium excretion and sodium reabsorption, leading to hyperkalemia, hyponatremia, and a decreased sodium-to-potassium ratio. These electrolyte abnormalities are hallmark features of primary hypoadrenocorticism. In secondary disease, electrolyte values typically remain normal because aldosterone secretion is intact. The 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines emphasized that electrolyte disturbances are a key diagnostic clue but must be interpreted in the context of other diseases (2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines, Journal of the American Animal Hospital Association, 2023, PubMed).

Clinical Presentation

Signalment and History

Feline hypoadrenocorticism can occur in cats of any age, breed, or sex, though most reported cases involve middle-aged to older cats. A review of feline endocrinopathies noted that affected cats typically present with a history of waxing and waning illness (Feline endocrinopathies, The Veterinary Clinics of North America: Small Animal Practice, 2005, PubMed). Owners may report intermittent lethargy, decreased appetite, vomiting, and weight loss over weeks to months. Some cats have a history of previous glucocorticoid administration, which may have partially masked clinical signs.

Physical Examination Findings

Physical examination findings in cats with hypoadrenocorticism are often nonspecific. Common findings include:

• Lethargy and depression
• Dehydration (often 5 to 8 percent)
• Poor body condition
• Hypothermia
• Weakness or collapse
• Bradycardia (related to hyperkalemia)
• Weak femoral pulses
• Abdominal pain (uncommon)

Cats rarely present with the classic "Addisonian crisis" seen in dogs, characterized by acute collapse, severe bradycardia, and hypovolemic shock. More commonly, feline hypoadrenocorticism follows a chronic, progressive course with subtle signs that mimic other diseases.

Differential Diagnoses

The clinical signs of feline hypoadrenocorticism overlap significantly with other common feline conditions. Veterinarians should consider hypoadrenocorticism in cats with:

• Chronic kidney disease (CKD): Both conditions can cause lethargy, anorexia, vomiting, and electrolyte abnormalities. However, CKD typically causes hyperkalemia with normal or low sodium, while hypoadrenocorticism causes hyponatremia and hyperkalemia.
• Hyperthyroidism: Weight loss, polyphagia, and hyperactivity are typical, hypoadrenocorticism usually causes anorexia and lethargy.
• Diabetes mellitus: Polyuria, polydipsia, and weight loss occur in both, hypoadrenocorticism may cause hypoglycemia.
• Gastrointestinal disease: Chronic vomiting and diarrhea are common to both.
• Hepatic disease: Lethargy, anorexia, and weight loss are shared signs.

Diagnostic Approach

Minimum Database

The diagnostic workup for suspected feline hypoadrenocorticism begins with a minimum database including complete blood count (CBC), serum biochemistry profile, and urinalysis. Key findings that raise suspicion include:

• Hyponatremia (sodium less than 145 mEq/L)
• Hyperkalemia (potassium greater than 5.5 mEq/L)
• Decreased sodium-to-potassium ratio (less than 27)
• Azotemia (prerenal or renal)
• Mild hypercalcemia (uncommon)
• Hypoglycemia (uncommon)
• Stress leukogram (neutrophilia, lymphopenia, eosinopenia) may be absent due to cortisol deficiency

The Merck Veterinary Manual notes that electrolyte abnormalities are a hallmark of primary hypoadrenocorticism but can occur with other conditions such as severe gastrointestinal disease, renal failure, or urinary tract obstruction (Merck Veterinary Manual, www.merckvetmanual.com). Therefore, electrolyte disturbances alone are not diagnostic.

ACTH Stimulation Test

The ACTH stimulation test is the gold standard for diagnosing hypoadrenocorticism in cats. The test evaluates adrenal cortisol reserve by measuring serum cortisol before and after administration of synthetic ACTH (cosyntropin). The 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines provide detailed protocols for performing and interpreting this test (2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines, Journal of the American Animal Hospital Association, 2023, PubMed).

Protocol considerations:

• Collect baseline blood sample for cortisol measurement.
• Administer synthetic ACTH (cosyntropin) at 5 mcg/kg intravenously or intramuscularly (maximum 250 mcg per cat).
• Collect post-ACTH blood sample at 60 minutes.
• Submit samples to a reference laboratory for cortisol measurement.

Interpretation:

• Normal response: Post-ACTH cortisol greater than 5 to 6 mcg/dL (varies by laboratory).
• Hypoadrenocorticism: Post-ACTH cortisol less than 2 mcg/dL with a blunted or absent response.
• Equivocal results: Post-ACTH cortisol between 2 and 5 mcg/dL may require repeat testing or additional diagnostics.

A 2024 update on feline hypoadrenocorticism emphasized that the ACTH stimulation test is reliable in cats but that reference intervals should be established by each laboratory (Hypoadrenocorticism in cats: a 40-year update, Journal of Feline Medicine and Surgery, 2024, PubMed). False-positive results can occur with exogenous glucocorticoid administration, which suppresses the HPA axis.

Aldosterone Measurement

Measurement of aldosterone concentration before and after ACTH stimulation can help differentiate primary from secondary hypoadrenocorticism. In primary disease, both cortisol and aldosterone responses are blunted. In secondary disease, cortisol response is blunted but aldosterone response is normal. A case report described hypoadrenocorticism diagnosed by ACTH stimulation test for aldosterone in a diabetic cat, highlighting the value of aldosterone assessment in complex cases (Hypoadrenocorticism diagnosed by adrenocorticotropin stimulation test for aldosterone in a diabetic cat, Israel Journal of Veterinary Medicine, 2014, Elsevier Scopus).

Endogenous ACTH Measurement

Measurement of endogenous ACTH concentration can help differentiate primary from secondary hypoadrenocorticism:

• Primary hypoadrenocorticism: Endogenous ACTH is elevated due to loss of negative feedback from cortisol deficiency.
• Secondary hypoadrenocorticism: Endogenous ACTH is low or inappropriately normal.

This test requires careful sample handling (collect in EDTA tube, centrifuge immediately, freeze plasma) and is not routinely available in all laboratories.

Imaging

Abdominal ultrasonography may reveal small adrenal glands in cats with chronic primary hypoadrenocorticism. However, normal adrenal size does not rule out the disease. Imaging is more useful for ruling out other causes of clinical signs (e.g., neoplasia, pancreatitis) than for diagnosing hypoadrenocorticism.

Treatment and Management

Acute Management of Addisonian Crisis

Cats presenting with acute hypoadrenocorticism (Addisonian crisis) require immediate stabilization. The goals of emergency therapy are to correct hypovolemia, electrolyte abnormalities, and glucocorticoid deficiency.

Fluid therapy:

• Administer 0.9% sodium chloride (normal saline) intravenously. This is the fluid of choice because it contains high sodium and no potassium.
• Initial bolus: 10 to 20 mL/kg over 15 to 30 minutes, repeated as needed based on perfusion parameters.
• Maintenance rate: 60 to 80 mL/kg/day after stabilization.
• Monitor electrolytes, blood pressure, and urine output.

Glucocorticoid replacement:

• Administer a rapid-acting glucocorticoid such as dexamethasone sodium phosphate (0.5 to 1 mg/kg IV) or prednisolone sodium succinate (5 to 10 mg/kg IV).
• Do not use dexamethasone if performing an ACTH stimulation test, as it may interfere with cortisol measurement.
• After initial stabilization, transition to oral prednisolone.

Electrolyte management:

• Hyperkalemia usually resolves with fluid therapy and glucocorticoid administration.
• Severe hyperkalemia (potassium greater than 7.0 mEq/L) causing bradycardia or cardiac arrhythmias may require additional therapy: calcium gluconate (0.5 to 1 mL/kg of 10% solution IV over 10 to 20 minutes), insulin with dextrose, or sodium bicarbonate.

Chronic Management

Long-term management of feline hypoadrenocorticism involves lifelong glucocorticoid and, if needed, mineralocorticoid replacement therapy.

Glucocorticoid replacement:

• Prednisolone is the preferred glucocorticoid in cats.
• Starting dose: 0.5 to 1 mg/kg orally every 24 hours, then taper to the lowest effective dose (typically 0.1 to 0.2 mg/kg every 24 to 48 hours).
• Adjust dose based on clinical signs (appetite, energy level, body weight).
• Avoid excessive glucocorticoid doses, which can cause iatrogenic hyperadrenocorticism.

Mineralocorticoid replacement:

• Required for cats with primary hypoadrenocorticism (aldosterone deficiency).
• Two options are available:
  • Desoxycorticosterone pivalate (DOCP): 2.2 mg/kg subcutaneously or intramuscularly every 25 to 30 days. Adjust dose and interval based on electrolyte monitoring.
  • Fludrocortisone acetate: 0.1 to 0.2 mg/kg orally every 12 to 24 hours. Starting dose is typically 0.1 mg/kg every 12 hours, then adjust based on electrolytes.
• DOCP is often preferred for cats because it requires less frequent administration and avoids oral dosing challenges.

Monitoring:

• Recheck electrolytes, blood urea nitrogen (BUN), creatinine, and clinical status 1 to 2 weeks after initiating therapy, then every 3 to 6 months once stable.
• Adjust mineralocorticoid dose to maintain sodium and potassium within reference intervals.
• Monitor for signs of over-replacement (hypertension, hypokalemia, polyuria, polydipsia) or under-replacement (lethargy, anorexia, electrolyte abnormalities).

The 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines recommend that veterinarians individualize therapy based on each cat's response and that owners be educated about signs of disease recurrence and the need for stress-dose glucocorticoids during illness or surgery (2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines, Journal of the American Animal Hospital Association, 2023, PubMed).

Stress Dosing

Cats with hypoadrenocorticism cannot mount an appropriate cortisol response to stress. Owners should be instructed to administer additional glucocorticoids during periods of illness, injury, or before procedures such as surgery or dental cleaning. A typical stress dose is 2 to 4 times the maintenance prednisolone dose for 1 to 3 days, then taper back to maintenance.

Practical Implementation Steps

Step 1: Recognize Clinical Suspicion

• Consider hypoadrenocorticism in any cat with chronic, waxing and waning lethargy, anorexia, vomiting, or weight loss.
• Maintain a low threshold for electrolyte screening, especially in cats with concurrent diseases such as CKD, hyperthyroidism, or diabetes mellitus.
• Document historical details: duration of signs, previous treatments (especially glucocorticoids), and response to therapy.

Step 2: Perform Minimum Database

• Collect blood for CBC, serum biochemistry, and urinalysis.
• Evaluate sodium, potassium, and sodium-to-potassium ratio.
• If electrolyte abnormalities are present, proceed to ACTH stimulation test.
• If electrolytes are normal but clinical suspicion remains high, consider ACTH stimulation test anyway (secondary hypoadrenocorticism may have normal electrolytes).

Step 3: Confirm Diagnosis with ACTH Stimulation Test

• Withhold any exogenous glucocorticoids for at least 24 to 48 hours before testing (longer for long-acting formulations).
• Collect baseline cortisol sample.
• Administer synthetic ACTH (cosyntropin) at 5 mcg/kg IV or IM.
• Collect post-ACTH cortisol sample at 60 minutes.
• Submit samples to a reference laboratory.
• Interpret results using laboratory-specific reference intervals.

Step 4: Differentiate Primary from Secondary Disease

• Measure aldosterone before and after ACTH stimulation if available.
• Measure endogenous ACTH concentration if primary vs. secondary distinction is clinically important.
• Consider abdominal ultrasound to assess adrenal gland size.

Step 5: Initiate Treatment

• For acute crisis: Administer IV fluids (0.9% NaCl) and rapid-acting glucocorticoid.
• For chronic management: Start prednisolone at 0.5 to 1 mg/kg orally every 24 hours.
• If primary disease confirmed or suspected: Add mineralocorticoid replacement (DOCP or fludrocortisone).
• Educate owner about stress dosing and monitoring.

Step 6: Monitor and Adjust Therapy

• Recheck electrolytes and clinical status 1 to 2 weeks after starting therapy.
• Adjust mineralocorticoid dose to maintain normal electrolytes.
• Taper glucocorticoid to lowest effective dose.
• Schedule rechecks every 3 to 6 months once stable.
• Monitor for complications: hypertension, hypokalemia, polyuria, polydipsia.

Records and Measurements

Essential Records to Maintain

• Diagnostic records: ACTH stimulation test results (baseline and post-ACTH cortisol, aldosterone if measured), electrolyte values, CBC, biochemistry profile, urinalysis.
• Treatment records: Drug name, dose, route, frequency, and any dose adjustments.
• Monitoring records: Serial electrolyte values, body weight, blood pressure, clinical assessment scores.
• Owner communication records: Instructions for stress dosing, signs of disease recurrence, emergency contact information.

Key Measurements to Track

Common Failure Patterns

Diagnostic Failures

• Failure to consider hypoadrenocorticism: Because feline hypoadrenocorticism is rare, many cases are initially misdiagnosed as CKD, gastrointestinal disease, or hyperthyroidism. Maintain a low index of suspicion.
• Normal electrolytes in secondary disease: Secondary hypoadrenocorticism does not cause electrolyte abnormalities. Relying solely on electrolyte screening will miss these cases.
• Interference from exogenous glucocorticoids: Recent glucocorticoid administration can suppress the HPA axis and cause false-positive ACTH stimulation test results. Obtain a thorough medication history.
• Inadequate ACTH dose: Using a suboptimal dose of cosyntropin may produce a blunted response. Follow published protocols.

Treatment Failures

• Inadequate mineralocorticoid dosing: Under-replacement leads to persistent electrolyte abnormalities and clinical signs. Adjust dose based on electrolyte monitoring.
• Excessive glucocorticoid dosing: Over-replacement causes iatrogenic hyperadrenocorticism (polyuria, polydipsia, weight gain, skin changes). Use the lowest effective dose.
• Failure to stress dose: Cats may develop Addisonian crisis during illness or surgery if glucocorticoid doses are not increased. Educate owners thoroughly.
• Poor owner compliance: Lifelong therapy and monitoring require owner commitment. Discuss the long-term nature of the disease and the consequences of noncompliance.

Monitoring Failures

• Infrequent electrolyte monitoring: Electrolyte abnormalities can develop gradually. Regular monitoring is essential for dose adjustment.
• Ignoring clinical signs: Owners may attribute lethargy or anorexia to aging or other diseases. Encourage prompt reporting of any changes.
• Not measuring blood pressure: Mineralocorticoid over-replacement can cause hypertension. Monitor blood pressure regularly.

Welfare and Safety Context

Animal Welfare Considerations

Feline hypoadrenocorticism is a manageable condition, but it requires lifelong treatment and monitoring. The World Organisation for Animal Health (WOAH) emphasizes that animal health management should prioritize prevention, early detection, and appropriate treatment of disease (Animal Health and Welfare, World Organisation for Animal Health, www.woah.org). For cats with hypoadrenocorticism, this means:

• Early diagnosis to prevent progression to Addisonian crisis.
• Appropriate treatment to maintain quality of life.
• Regular monitoring to detect and correct complications.
• Owner education to ensure compliance and recognition of disease recurrence.

Safety Considerations for Veterinary Personnel

• Glucocorticoid and mineralocorticoid medications are controlled substances in some jurisdictions. Maintain proper inventory and prescription records.
• DOCP is a long-acting injectable, ensure proper dosing and administration technique to avoid overdosing.
• Fludrocortisone is an oral medication, educate owners about proper dosing and storage.

Regulatory Context

• Glucocorticoids and mineralocorticoids are prescription medications. Veterinarians must comply with local regulations regarding prescribing, dispensing, and record-keeping.
• The 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines provide evidence-based recommendations for diagnosis and management but do not constitute regulatory requirements (2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines, Journal of the American Animal Hospital Association, 2023, PubMed).
• The American College of Veterinary Internal Medicine (ACVIM) provides consensus statements and guidelines for endocrine disease management (American College of Veterinary Internal Medicine, www.acvim.org).

Professional Escalation Criteria

When to Refer to a Specialist

• Diagnostic uncertainty: If ACTH stimulation test results are equivocal or if differentiation between primary and secondary disease is unclear, consider referral to a veterinary internal medicine specialist.
• Poor response to therapy: If a cat does not improve with appropriate glucocorticoid and mineralocorticoid replacement, referral is warranted to rule out concurrent disease or complications.
• Complex concurrent disease: Cats with hypoadrenocorticism and other endocrine disorders (e.g., diabetes mellitus, hyperthyroidism) may benefit from specialist management.
• Adverse effects of therapy: If a cat develops hypertension, hypokalemia, or other complications that are difficult to manage, referral may be appropriate.

When to Seek Emergency Care

• Addisonian crisis: Acute collapse, severe bradycardia, hypovolemic shock, or severe electrolyte abnormalities (potassium greater than 7.0 mEq/L, sodium less than 130 mEq/L) require immediate emergency intervention.
• Uncontrolled vomiting or diarrhea: May indicate disease recurrence or a stressor requiring increased glucocorticoid doses.
• Neurologic signs: Seizures, ataxia, or altered mentation may indicate severe electrolyte disturbances or other complications.

Practical Decision Framework for Adjusting Mineralocorticoid and Glucocorticoid Therapy in Feline Hypoadrenocorticism

Managing feline hypoadrenocorticism requires ongoing dose adjustments based on clinical and laboratory parameters. Unlike canine patients, cats exhibit greater individual variation in drug metabolism and sensitivity, making a structured decision framework essential for optimizing therapy. This section provides a practical, evidence-informed approach to adjusting mineralocorticoid and glucocorticoid replacement, including specific decision thresholds, monitoring intervals, and troubleshooting strategies for common clinical scenarios.

Decision Framework for Mineralocorticoid Dose Adjustment

Mineralocorticoid replacement is required for cats with primary hypoadrenocorticism, which is the more common form in this species (Hypoadrenocorticism in cats: a 40-year update, Journal of Feline Medicine and Surgery, 2024, PubMed). The two available options are desoxycorticosterone pivalate (DOCP) administered subcutaneously or intramuscularly every 25 to 30 days, and oral fludrocortisone acetate given every 12 to 24 hours. The decision framework below applies to both formulations, though monitoring intervals differ slightly due to pharmacokinetic differences.

Initial Stabilization Period (First 4 Weeks)

During the first month of therapy, electrolyte monitoring should occur at weekly intervals. The target ranges for serum sodium and potassium are the same as for healthy cats, typically 145 to 155 mEq/L for sodium and 3.5 to 5.5 mEq/L for potassium. The sodium-to-potassium ratio should be greater than 27. The Merck Veterinary Manual notes that electrolyte abnormalities are a hallmark of primary hypoadrenocorticism and that normalization of these values is the primary goal of mineralocorticoid therapy (Merck Veterinary Manual, www.merckvetmanual.com).

Decision points at each weekly recheck:

• If both sodium and potassium are within reference intervals and the cat is clinically normal, maintain the current dose and interval.
• If sodium is below 145 mEq/L or potassium is above 5.5 mEq/L, increase the mineralocorticoid dose by 10 to 20 percent. For DOCP, this may mean increasing the dose per injection or shortening the interval to 21 to 24 days. For fludrocortisone, increase the dose or divide the daily dose into more frequent administration.
• If sodium is above 155 mEq/L or potassium is below 3.5 mEq/L, decrease the mineralocorticoid dose by 10 to 20 percent. For DOCP, extend the interval to 30 to 35 days or reduce the dose. For fludrocortisone, reduce the dose or frequency.
• If sodium is above 160 mEq/L or potassium is below 3.0 mEq/L, hold the next mineralocorticoid dose and recheck electrolytes in 3 to 5 days. These values indicate over-replacement and risk of hypertension or hypokalemia-related weakness.

Stable Maintenance Period (After 4 Weeks)

Once electrolytes have been stable for two consecutive weekly rechecks, the monitoring interval can be extended to every 3 to 6 months. The 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines recommend that veterinarians individualize therapy based on each cat's response and that monitoring should include serum electrolytes, blood pressure, and clinical assessment (2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines, Journal of the American Animal Hospital Association, 2023, PubMed).

Decision points at each stable recheck:

• If electrolytes are within reference intervals and the cat is clinically normal, continue the current regimen.
• If electrolytes are mildly abnormal (sodium 140 to 144 mEq/L or potassium 5.6 to 6.0 mEq/L) but the cat is clinically normal, consider a small dose adjustment of 5 to 10 percent and recheck in 2 to 4 weeks.
• If electrolytes are moderately abnormal (sodium less than 140 mEq/L or potassium greater than 6.0 mEq/L) or the cat shows clinical signs (lethargy, anorexia, vomiting), adjust the dose by 10 to 20 percent and recheck in 1 to 2 weeks.
• If electrolytes are severely abnormal (sodium less than 130 mEq/L or potassium greater than 7.0 mEq/L) or the cat is in crisis, provide emergency care as described in the acute management section and recheck electrolytes within 24 to 48 hours.

Decision Framework for Glucocorticoid Dose Adjustment

Glucocorticoid replacement is required for all cats with hypoadrenocorticism, regardless of whether the disease is primary or secondary. Prednisolone is the preferred glucocorticoid in cats due to its reliable absorption and predictable effects. The goal is to use the lowest effective dose that maintains normal appetite, energy level, and body weight without causing signs of hypercortisolism.

Initial Stabilization Period (First 4 Weeks)

Start prednisolone at 0.5 to 1 mg/kg orally every 24 hours. After the first week, assess clinical response and begin tapering. A review of feline endocrinopathies noted that cats often require lower glucocorticoid doses than dogs and that excessive dosing can lead to iatrogenic hyperadrenocorticism (Feline endocrinopathies, The Veterinary Clinics of North America: Small Animal Practice, 2005, PubMed).

Decision points at weekly rechecks:

• If the cat has normal appetite, normal energy level, and stable body weight, decrease the prednisolone dose by 25 to 50 percent every 1 to 2 weeks until the lowest effective dose is reached. The typical maintenance dose is 0.1 to 0.2 mg/kg every 24 to 48 hours.
• If the cat shows signs of glucocorticoid deficiency (lethargy, anorexia, vomiting, weight loss), increase the dose to the previous level and taper more slowly.
• If the cat shows signs of glucocorticoid excess (polyuria, polydipsia, polyphagia, weight gain, skin thinning, muscle wasting), decrease the dose by 25 to 50 percent and monitor for resolution of signs.

Stable Maintenance Period (After 4 Weeks)

Once the cat is stable on a low maintenance dose, monitoring can be extended to every 3 to 6 months. Owners should be educated to recognize signs of both under-replacement and over-replacement and to contact the veterinarian if these occur.

Decision points at each stable recheck:

• If the cat is clinically normal on the current dose, continue the same regimen.
• If the cat shows mild lethargy or decreased appetite, consider a temporary increase of 25 to 50 percent for 3 to 5 days. If signs resolve, return to the maintenance dose. If signs persist, a more sustained increase may be needed.
• If the cat shows signs of hypercortisolism, decrease the dose by 25 percent and recheck in 2 to 4 weeks.

Stress Dosing Decision Framework

Cats with hypoadrenocorticism cannot mount an appropriate cortisol response to stress. The 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines emphasize that owners should be instructed to administer additional glucocorticoids during periods of illness, injury, or before procedures such as surgery or dental cleaning (2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines, Journal of the American Animal Hospital Association, 2023, PubMed).

Decision points for stress dosing:

• For minor stress (mild illness, vaccination, travel): Increase prednisolone to 2 times the maintenance dose for 1 to 2 days, then return to maintenance.
• For moderate stress (vomiting, diarrhea, minor surgery, dental cleaning): Increase prednisolone to 3 to 4 times the maintenance dose for 2 to 3 days, then taper over 3 to 5 days back to maintenance.
• For severe stress (major surgery, trauma, critical illness): Administer injectable glucocorticoid (dexamethasone sodium phosphate 0.5 to 1 mg/kg IV or prednisolone sodium succinate 5 to 10 mg/kg IV) and provide supportive care. Transition to oral prednisolone at 3 to 4 times maintenance once the cat is eating and drinking, then taper over 5 to 7 days.
• If the cat cannot take oral medication due to vomiting or anorexia, administer injectable glucocorticoid and seek veterinary care.

Record System for Therapy Adjustments

A structured record system is essential for tracking therapy adjustments and monitoring trends. The following template can be used for each patient:

Patient Record Template:

Clinical assessment categories:

• Normal: Normal appetite, energy, body weight, no vomiting or diarrhea
• Mild deficiency: Mild lethargy, slightly decreased appetite, no vomiting
• Moderate deficiency: Moderate lethargy, anorexia, occasional vomiting
• Severe deficiency: Collapse, severe lethargy, persistent vomiting, dehydration
• Mild excess: Mild polyuria, polydipsia, increased appetite
• Moderate excess: Marked polyuria, polydipsia, weight gain, skin changes
• Severe excess: Severe polyuria, polydipsia, muscle wasting, hypertension

Common Failure Patterns in Therapy Adjustment

Failure to Recognize Under-Replacement

Under-replacement of mineralocorticoid leads to persistent hyponatremia and hyperkalemia, which can cause lethargy, anorexia, vomiting, and weakness. In severe cases, hyperkalemia can cause bradycardia and cardiac arrhythmias. A case report described hypoadrenocorticism diagnosed by ACTH stimulation test for aldosterone in a diabetic cat, highlighting that electrolyte abnormalities may be subtle and require careful monitoring (Hypoadrenocorticism diagnosed by adrenocorticotropin stimulation test for aldosterone in a diabetic cat, Israel Journal of Veterinary Medicine, 2014, Elsevier Scopus).

Troubleshooting steps:

• Verify that the mineralocorticoid dose is appropriate for the cat's body weight.
• Check that the dosing interval is correct (every 25 to 30 days for DOCP, every 12 to 24 hours for fludrocortisone).
• Consider whether concurrent medications (e.g., potassium-sparing diuretics, ACE inhibitors) are affecting electrolyte balance.
• Rule out other causes of electrolyte abnormalities, such as chronic kidney disease, urinary tract obstruction, or gastrointestinal disease.

Failure to Recognize Over-Replacement

Over-replacement of mineralocorticoid causes hypertension, hypokalemia, and polyuria. Over-replacement of glucocorticoid causes iatrogenic hyperadrenocorticism with polyuria, polydipsia, polyphagia, weight gain, skin thinning, and muscle wasting. The Merck Veterinary Manual notes that iatrogenic hyperadrenocorticism is a potential complication of glucocorticoid therapy in cats (Merck Veterinary Manual, www.merckvetmanual.com).

Troubleshooting steps:

• Reduce the mineralocorticoid or glucocorticoid dose by 10 to 20 percent.
• Monitor blood pressure and electrolytes weekly until normalized.
• If hypertension persists despite dose reduction, consider antihypertensive therapy and referral to a specialist.
• If hypokalemia persists, consider potassium supplementation and further dose reduction.

Failure to Adjust for Weight Changes

Body weight changes affect drug distribution and clearance. A cat that gains weight may require a higher absolute dose, while a cat that loses weight may require a lower dose. The 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines recommend that veterinarians adjust doses based on body weight and clinical response (2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines, Journal of the American Animal Hospital Association, 2023, PubMed).

Troubleshooting steps:

• Weigh the cat at every recheck.
• Calculate the current dose in mg/kg and compare to the target range.
• Adjust the dose to maintain the same mg/kg target.
• Recheck electrolytes 1 to 2 weeks after any dose adjustment.

Failure to Account for Concurrent Disease

Concurrent diseases can affect drug metabolism and electrolyte balance. For example, chronic kidney disease can cause electrolyte abnormalities that mimic or mask hypoadrenocorticism. Hyperthyroidism can increase drug metabolism and require higher doses. Diabetes mellitus can be destabilized by glucocorticoid therapy.

Troubleshooting steps:

• Monitor all concurrent diseases and their treatments.
• Adjust hypoadrenocorticism therapy based on the cat's overall clinical status, beyond electrolyte values.
• Consider referral to a veterinary internal medicine specialist for complex cases.

Welfare and Safety Context for Therapy Adjustment

The World Organisation for Animal Health (WOAH) emphasizes that animal health management should prioritize prevention, early detection, and appropriate treatment of disease (Animal Health and Welfare, World Organisation for Animal Health, www.woah.org). For cats with hypoadrenocorticism, appropriate therapy adjustment is critical for maintaining quality of life and preventing complications.

Welfare considerations:

• Under-replacement causes chronic malaise, weakness, and risk of Addisonian crisis.
• Over-replacement causes polyuria, polydipsia, and risk of hypertension and iatrogenic hyperadrenocorticism.
• Frequent monitoring and dose adjustments are necessary to maintain optimal health.
• Owner education is essential for recognizing signs of under- or over-replacement and for administering stress doses.

Safety considerations:

• DOCP is a long-acting injectable, overdosing can cause prolonged electrolyte abnormalities.
• Fludrocortisone is an oral medication, missed doses can lead to rapid electrolyte derangement.
• Glucocorticoids should never be abruptly discontinued, taper doses gradually.
• Stress dosing should be discussed with the veterinarian before implementation.

Professional Escalation Criteria for Therapy Adjustment

When to refer to a specialist:

• Persistent electrolyte abnormalities despite appropriate dose adjustments.
• Difficulty differentiating primary from secondary disease.
• Concurrent endocrine disorders (diabetes mellitus, hyperthyroidism, hyperadrenocorticism).
• Adverse effects of therapy that are difficult to manage (severe hypertension, hypokalemia, iatrogenic hyperadrenocorticism).
• Poor owner compliance or understanding of the treatment plan.

When to seek emergency care:

• Acute collapse, severe bradycardia, or hypovolemic shock.
• Severe electrolyte abnormalities (potassium greater than 7.0 mEq/L, sodium less than 130 mEq/L).
• Uncontrolled vomiting or diarrhea with inability to take oral medication.
• Neurologic signs (seizures, ataxia, altered mentation).

The American College of Veterinary Internal Medicine (ACVIM) provides consensus statements and guidelines for endocrine disease management and can be a resource for veterinarians managing complex cases (American College of Veterinary Internal Medicine, www.acvim.org).

Frequently Asked Questions

What is the difference between primary and secondary hypoadrenocorticism in cats?

Primary hypoadrenocorticism results from destruction of the adrenal cortex, causing deficiency of both cortisol and aldosterone. Secondary hypoadrenocorticism results from deficient pituitary ACTH secretion, causing isolated cortisol deficiency with normal aldosterone production. Primary disease is more common in cats and requires both glucocorticoid and mineralocorticoid replacement, while secondary disease requires only glucocorticoid replacement.

How is feline hypoadrenocorticism diagnosed?

The gold standard diagnostic test is the ACTH stimulation test, which measures serum cortisol before and after administration of synthetic ACTH. A blunted or absent cortisol response confirms the diagnosis. Electrolyte abnormalities (hyponatremia, hyperkalemia, decreased sodium-to-potassium ratio) are suggestive but not diagnostic. Aldosterone measurement and endogenous ACTH measurement can help differentiate primary from secondary disease.

What are the most common clinical signs of hypoadrenocorticism in cats?

The most common clinical signs are chronic, waxing and waning lethargy, anorexia, vomiting, and weight loss. Some cats also exhibit polyuria, polydipsia, or weakness. Physical examination findings may include dehydration, hypothermia, bradycardia, and poor body condition. Acute Addisonian crisis with collapse and shock is less common in cats than in dogs.

Can hypoadrenocorticism in cats be cured?

No, hypoadrenocorticism is not curable. It requires lifelong replacement therapy with glucocorticoids and, if primary disease, mineralocorticoids. However, with appropriate treatment and monitoring, most cats have a good prognosis and can maintain a normal quality of life.

What is the treatment for feline hypoadrenocorticism?

Treatment involves glucocorticoid replacement (prednisolone) and, for primary disease, mineralocorticoid replacement (desoxycorticosterone pivalate or fludrocortisone). Acute Addisonian crisis requires intravenous fluid therapy (0.9% sodium chloride) and rapid-acting glucocorticoids. Long-term management includes regular monitoring of electrolytes and clinical status, with dose adjustments as needed.

How often should a cat with hypoadrenocorticism be monitored?

After initiating therapy, electrolytes and clinical status should be rechecked in 1 to 2 weeks. Once stable, rechecks every 3 to 6 months are recommended. Monitoring includes serum sodium, potassium, BUN, creatinine, body weight, and blood pressure. Owners should also monitor for signs of disease recurrence and report any changes promptly.

What should I do if my cat with hypoadrenocorticism becomes ill or needs surgery?

Cats with hypoadrenocorticism cannot produce adequate cortisol in response to stress. During illness, injury, or before procedures such as surgery or dental cleaning, the glucocorticoid dose should be increased to 2 to 4 times the maintenance dose for 1 to 3 days, then tapered back. Owners should discuss stress dosing with their veterinarian and have a plan in place for emergencies.

Are there any breed or sex predispositions for feline hypoadrenocorticism?

No strong breed or sex predispositions have been identified for feline hypoadrenocorticism. The condition can occur in any cat, though most reported cases involve middle-aged to older cats. The rarity of the disease means that any cat with compatible clinical signs should be evaluated, regardless of signalment.

Related Veterinary Guides

• Cat
• Chronic Kidney Disease In Cats
• Symptoms Of Kidney Disease In My Cat
• Symptoms Of Kidney Disease In Old Cats
• Symptoms Of Kidney Disease In Senior Cats

References and Further Reading

• www.merckvetmanual.com
• catvets.com
• www.acvim.org
• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Canine hypoadrenocorticism: pathogenesis, diagnosis, and treatment.. Topics in companion animal medicine, 2014.
• 2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines.. Journal of the American Animal Hospital Association, 2023.
• Hypoadrenocorticism in cats: a 40-year update.. Journal of feline medicine and surgery, 2024.
• Feline hypoadrenocorticism: Emerging insights into clinical features, diagnosis, and treatment.. Schweizer Archiv fur Tierheilkunde, 2026.
• Pituitary deficiencies.. Topics in companion animal medicine, 2012.
• Feline endocrinopathies.. The Veterinary clinics of North America. Small animal practice, 2005.
• Two cases of feline hypoadrenocorticism. Veterinaria, 2012.
• Hypoadrenocorticism diagnosed by adrenocorticotropin stimulation test for aldosterone in a diabetic cat. Israel Journal of Veterinary Medicine, 2014.

This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.