Hyperadrenocorticism (Cushing's syndrome) is a common endocrine disorder of middle-aged to older dogs caused by chronic excess cortisol. It significantly affects quality of life and requires careful, often lifelong management. Early recognition and appropriate treatment substantially improves welfare outcomes.
Causes
85–90% of cases are pituitary-dependent (PDH) — a benign pituitary tumour secretes excess ACTH, stimulating bilateral adrenal enlargement and cortisol overproduction. 10–15% are adrenal-dependent — a unilateral adrenal tumour (benign or malignant) independently secretes cortisol. Iatrogenic Cushing's (from prolonged corticosteroid administration) is also common and resolves with careful dose reduction.
Clinical Signs
- Pot-bellied abdomen (muscle wasting + liver enlargement)
- Polydipsia and polyuria (PU/PD)
- Polyphagia (increased appetite)
- Symmetrical alopecia (bilateral hair loss), skin thinning and calcinosis cutis
- Muscle weakness and exercise intolerance
- Panting and heat intolerance
- Increased susceptibility to infections (UTI, skin infections)
Diagnosis
Screening tests include the low-dose dexamethasone suppression test (LDDS) and urine cortisol:creatinine ratio. The high-dose dexamethasone suppression test and ACTH stimulation test help differentiate PDH from adrenal-dependent disease. Abdominal ultrasound identifies adrenal size and asymmetry. Advanced imaging (MRI) may identify large pituitary tumours.
Medical Treatment
Trilostane (Vetoryl): First-line treatment for PDH in the UK and EU. Inhibits adrenal steroidogenesis. Requires careful dose titration with monitoring (ACTH stimulation test at 10 days, 4 weeks, and then every 3–6 months). Side effects include acute hypoadrenocorticism — owners must recognise signs and seek emergency care.
Mitotane (o,p'-DDD): Selectively destroys adrenal cortex; used in some countries; requires careful induction and maintenance protocols.
Surgical adrenalectomy: For adrenal-dependent disease; specialist procedure with significant perioperative risk.
Welfare Impact and Monitoring
Untreated Cushing's causes chronic suffering — PU/PD disrupts sleep and normal behaviour; muscle weakness causes mobility difficulties; skin changes cause discomfort; increased infection susceptibility reduces resilience. Well-treated dogs show dramatic improvement: reduced PU/PD, improved coat, muscle tone, and activity. Regular monitoring (every 3–6 months minimum) ensures dose remains appropriate as disease evolves over time.