- Endocrine Etiology: Canine hyperadrenocorticism (Cushing’s disease) is characterized by chronic overproduction of circulating cortisol, driven either by a pituitary adenoma (80–85% of cases) or a functional adrenal tumor (15–20%).
- The Classic Triad: The clinical presentation centers on polydipsia/polyuria (excessive thirst and urination), polyphagia (ravenous hunger), and bilateral endocrine alopecia with a characteristic pot-bellied abdominal distension caused by hepatomegaly and abdominal muscle catabolism.
- Diagnostic Distinction: Screening requires an LDDS (Low-Dose Dexamethasone Suppression) test or ACTH Stimulation test; monitoring therapeutic response to Trilostane (Vetoryl) mandates pre-pill or post-pill ACTH stimulation testing to prevent life-threatening Addisonian crises.
Canine hyperadrenocorticism—universally termed Cushing’s disease—represents one of the most frequently misdiagnosed endocrine pathologies in middle-aged and geriatric dogs. Because the insidious onset of excessive thirst, urinary accidents, panting, and muscle weakness is frequently dismissed by caregivers as normal aging, early diagnostic interventions are routinely missed.
Unchecked chronic hypercortisolemia wreaks havoc on canine longevity: it induces systemic hypertension, causes severe proteinuria, promotes hypercoagulability leading to pulmonary thromboembolism, and suppresses cell-mediated immunity, sparking recurrent urinary tract and dermatological infections.
What Are the Early Symptoms of Cushing’s Disease in Dogs?
Review baseline laboratory diagnostics in our detailed guide to Senior Dog Bloodwork: Chemistry & CBC Lab Guide, and investigate hepatic indicators via Elevated Liver Enzymes in Dogs: ALT & ALP Guide.
Diagnostic Testing: ACTH Stimulation vs. Low-Dose Dexamethasone Suppression
Differentiating between pituitary-dependent hyperadrenocorticism (PDH) and adrenal-dependent tumors requires specific endocrinological testing protocols:
| Diagnostic Test | Protocol & Timing | Sensitivity / Specificity | Clinical Utility |
|---|---|---|---|
| LDDS Test | Baseline cortisol, 0.01 mg/kg Dex IV, retest at 4h and 8h | Sensitivity: 85–95% | Specificity: 70–75% | Gold standard screening test; can differentiate PDH from adrenal tumors in 60% of cases |
| ACTH Stimulation Test | Baseline cortisol, synthetic ACTH IV, retest cortisol at 1 hour | Sensitivity: 60–80% | Specificity: 85–90% | Only test valid for iatrogenic Cushing’s and mandatory for monitoring Trilostane therapy |
| Urine Cortisol:Creatinine (UCCR) | Home-collected morning urine free of veterinary stress | Sensitivity: >95% | Specificity: 20–25% | Excellent “rule-out” test; a normal result eliminates Cushing’s with near certainty |
| Abdominal Ultrasound | High-frequency probe measuring bilateral adrenal gland thickness | Operator dependent | Identifies adrenal asymmetry, vascular invasion of caudal vena cava, and hepatomegaly |
Trilostane (Vetoryl) Titration: Avoiding Hypoadrenocorticism
Trilostane operates as a competitive inhibitor of 3-beta-hydroxysteroid dehydrogenase, an enzyme system essential for adrenocortical synthesis of cortisol, aldosterone, and corticosterone. Modern veterinary endocrinology consensus (ACVIM) recommends starting with a low, twice-daily dosing regimen (0.5–1.0 mg/kg BID with meals) rather than the older high-dose once-daily label recommendation, which frequently resulted in adrenal necrosis.
Serial monitoring with ACTH stimulation testing is performed at 2 to 4 weeks, 12 weeks, and every 6 months thereafter. Caregivers must be educated on early symptoms of hypocortisolemia: lethargy, vomiting, inappetence, and weakness. If observed, Trilostane must be withheld immediately and dexamethasone administered to avert acute hypovolemic shock.
Cushing’s disease is an endocrine condition that requires measured, precision titration rather than aggressive suppression. By prioritizing twice-daily low-dose Trilostane, conducting serial ACTH stimulation monitoring, and screening for hypertension and microalbuminuria, canine patients can achieve complete clinical remission, reversing alopecia and muscle atrophy while restoring high-quality longevity.