Cushing's Syndrome

Cushing's syndrome (hyperadrenocorticism) results from chronically elevated cortisol levels. In 85–90% of cases, the cause is a pituitary tumour producing excessive ACTH (which stimulates the adrenal glands to produce cortisol) - this is called pituitary-dependent hyperadrenocorticism (PDH). In 10–15% of cases, a tumour in the adrenal gland itself overproduces cortisol - adrenal-dependent hyperadrenocorticism (ADH). A third form, iatrogenic Cushing's, is caused by prolonged steroid administration.

The condition develops slowly over months to years, which is why it's often initially attributed to normal ageing.

Classic signs

Log changes in these areas:

Polydipsia and polyuria (PD/PU). Dramatically increased water intake and urination are among the earliest and most consistent signs. Note whether your dog is drinking noticeably more than usual - a useful reference point is whether they're emptying the bowl more quickly or asking for water more often.

Pot-bellied appearance. Cortisol causes fat redistribution to the abdomen and muscle wasting from the limbs. The abdomen appears pendulous and rounded even if the dog hasn't gained overall weight. Note changes in abdominal profile.

Hair loss. Usually symmetrical on the body - trunk, flanks - but sparing the head and limbs. Alopecia (hair loss) without itching is characteristic.

Skin changes. Thin, fragile skin that tears or bruises easily; darkening (hyperpigmentation); calcinosis cutis (calcium deposits under the skin, appearing as white or chalky plaques, often along the back).

Lethargy and exercise intolerance. Often assumed to be ageing.

Increased appetite. Often described by owners as the dog becoming ravenous.

Panting. Increased panting, particularly at rest or when not hot.

Muscle weakness. Weakness in the legs, difficulty jumping or climbing.

Diagnosis

Cushing's is diagnosed through a combination of clinical signs and hormonal testing. Common tests include:

• Low dose dexamethasone suppression test (LDDST) - the most sensitive test; measures cortisol before and after a dexamethasone injection
• ACTH stimulation test - less sensitive for diagnosis, but used to monitor treatment
• Urine cortisol:creatinine ratio - a useful screening test, but with poor specificity (many other conditions can cause a raised result)

Distinguishing pituitary from adrenal-dependent Cushing's uses the high dose dexamethasone suppression test or abdominal ultrasound.

Treatment

PDH (pituitary-dependent): Oral medication - trilostane (Vetoryl) is the most commonly used in the UK. Trilostane inhibits cortisol synthesis in the adrenal glands. Monitoring is required: ACTH stimulation tests at 10 days, 4 weeks, then every 3–6 months.

ADH (adrenal-dependent): Surgical removal of the affected adrenal gland is curative where feasible; trilostane is used where surgery is not possible.

Iatrogenic Cushing's: Gradual reduction and cessation of steroid medication under veterinary supervision.

Monitoring at home on treatment

Log weekly:

• Water intake (cups or litres per day if quantifying)
• Urination frequency
• Appetite
• Energy level
• Panting
• Any signs of hypoadrenocorticism (under-treatment - see below)

Signs of overtreatment (adrenal crisis/Addisonian crisis): Lethargy, vomiting, diarrhoea, weakness, collapse. Trilostane works by suppressing cortisol production - too much suppression causes dangerously low cortisol levels. Know these signs and contact your vet immediately if they appear.

When to contact your vet

Contact your vet urgently if:

• Signs of adrenal crisis (lethargy, vomiting, weakness, collapse) - stop trilostane and seek emergency care
• Worsening of Cushing's signs despite treatment

Schedule a routine appointment for:

• ACTH stimulation monitoring (10 days and 4 weeks after starting or changing trilostane dose, then regularly)
• Dose adjustment based on monitoring results
• Annual blood and urine screens

Frequently Asked Questions

Can Cushing's be cured? PDH is managed, not cured - most dogs require lifelong trilostane with monitoring. Adrenal-dependent Cushing's can potentially be cured with surgery. Iatrogenic Cushing's resolves when steroids are withdrawn.

My dog has Cushing's - what's the prognosis? Well-managed Cushing's with good monitoring carries a reasonable prognosis. Most dogs with PDH survive 2–3 years after diagnosis on treatment, with many living considerably longer. Adrenal tumours are more variable. Regular monitoring is essential to maintain good quality of life.

Is Cushing's painful? The condition itself is not typically painful, but some secondary effects - calcinosis cutis, skin infections - can cause discomfort. Muscle weakness can make movement harder. Dogs generally seem comfortable when well-controlled on treatment.

Can I skip the monitoring blood tests to save money? The monitoring tests are important for safety, not just information. Trilostane overdosage can cause a life-threatening adrenal crisis; monitoring identifies when doses need adjustment before this happens. Skipping monitoring is genuinely risky.

How do I know if the treatment is working? Improvement typically appears over 1–3 months: reduced water intake, less urination, better energy, reduction in pot belly. Hair may regrow slowly. ACTH stimulation test results should reflect adequate cortisol suppression without over-suppression.