Cushing's disease (hyperadrenocorticism) is the overproduction of cortisol by the adrenal glands. It is one of the most frequently diagnosed endocrine conditions in middle-aged to older dogs, yet it remains one of the most under-diagnosed because its symptoms look like "normal aging." Excessive thirst, increased urination, pot belly, panting — owners attribute these to getting old, not to a treatable hormonal disease.
Types
| Type | Cause | Frequency |
|---|---|---|
| Pituitary-dependent (PDH) | Pituitary gland tumor overproducing ACTH → adrenal glands overproduce cortisol | 80-85% of cases |
| Adrenal tumor | Tumor on one adrenal gland producing cortisol autonomously | 15-20% of cases |
| Iatrogenic | Long-term steroid medication causing Cushing-like symptoms | Common but resolves when steroids discontinued |
Symptoms
- Polyuria/Polydipsia (PU/PD): Excessive urination and thirst — often the first sign noticed
- Pot belly: Muscle wasting + fat redistribution + liver enlargement + weakened abdominal muscles
- Panting: Increased respiratory rate even at rest
- Increased appetite (polyphagia)
- Skin changes: Thin skin, slow wound healing, recurrent skin infections, hair loss (symmetric bilateral), calcinosis cutis (calcium deposits in skin)
- Muscle weakness/wasting
- Recurrent urinary tract infections (cortisol suppresses immune function)
Diagnosis
Cushing's is one of the most diagnostically challenging conditions in veterinary medicine. No single test is definitive:
- Screening tests: Urine cortisol:creatinine ratio (highly sensitive, not specific — good for ruling OUT Cushing's)
- Low-dose dexamethasone suppression test (LDDS): Most commonly used confirmatory test. 8-hour test measuring cortisol response to dexamethasone injection.
- ACTH stimulation test: Measures adrenal response to synthetic ACTH. Also used for monitoring treatment.
- Abdominal ultrasound: Evaluates adrenal gland size and symmetry. Identifies adrenal tumors.
- High-dose dexamethasone suppression: Differentiates pituitary vs. adrenal origin.
Treatment
Trilostane (Vetoryl) — First-Line
- Blocks cortisol production (competitive enzyme inhibitor)
- Given daily with food
- ACTH stimulation tests at 2 weeks, 4 weeks, 8 weeks, then every 3-4 months to adjust dose
- Well-tolerated; most dogs improve within 2-4 weeks
- Cost: $50-$150/month depending on dog size
Mitotane (Lysodren) — Second-Line
- Destroys cortisol-producing adrenal tissue (more aggressive than trilostane)
- Requires careful induction and monitoring (risk of adrenal crisis)
- Effective but narrower safety margin
- Less commonly used since trilostane became available
Surgery (Adrenalectomy)
For adrenal tumors: surgical removal is potentially curative. High-risk surgery requiring specialist surgeon. Not an option for pituitary-dependent Cushing's in most cases.
Frequently Asked Questions
Can Cushing's be cured?
Adrenal tumor cases: yes, if surgically removed successfully. Pituitary-dependent cases: managed, not cured. Trilostane controls cortisol levels but the underlying pituitary tumor remains. Most dogs live 2-4 years post-diagnosis with good quality of life on medication.
What happens if Cushing's is not treated?
Progressive muscle wasting, skin fragility, increased infection susceptibility, diabetes development, pulmonary thromboembolism (blood clots in lungs — can be fatal), and declining quality of life. Treatment significantly improves comfort and potentially extends life.
