Canine Cushing's Disease: Causes, Symptoms & Treatments

Canine Cushing's disease (also known as hyperadrenocorticism) is a frequent hormonal disorder in dogs, especially older ones, caused by an overproduction of cortisol, a vital hormone that regulates stress, metabolism, and immune function. This comprehensive guide explains the causes, symptoms, diagnosis, and treatment options to help you support your dog's health and wellbeing.

Understanding Canine Cushing's Disease

Cushing's disease arises when cortisol levels become excessively high, either due to tumours in the pituitary or adrenal glands or from prolonged steroid medication use. Cortisol is normally released to help dogs respond to stress and regulate bodily functions, but excess cortisol can damage their health over time.

Types of Cushing's Disease

1. Pituitary-Dependent: Approximately 85-90% of dogs with Cushing's have a benign tumour in the pituitary gland, causing excessive ACTH hormone that overstimulates the adrenal glands to produce cortisol. These tumours usually grow slowly and mainly affect hormone regulation.
2. Adrenal-Dependent: About 10-15% of cases stem from tumours in one or both adrenal glands themselves. These tumours can be benign or malignant, with malignant tumours sometimes spreading to other organs like the lungs. Diagnosis is necessary to determine tumour type and treatment options.
3. Iatrogenic (Medication-Induced): Long-term use of steroid medications (e.g., prednisolone) for other medical conditions can mimic Cushing's disease by increasing cortisol levels. It is vital these medications are used under veterinary supervision to minimise risks.

Recognising Symptoms of Canine Cushing's

Cushing's disease often develops gradually, with symptoms sometimes overlooked by owners until they become more pronounced. Common signs include:

• Increased thirst and drinking (polydipsia)
• Frequent and large-volume urination (polyuria), sometimes leading to incontinence
• Increased appetite, often resulting in weight gain
• Noticeable panting even at rest
• Progressive hair loss, especially on the body but sparing the head and legs, usually without itching
• Thinning skin that may bruise easily
• A swollen abdomen or 'pot belly' appearance caused by fat redistribution and muscle loss
• Muscle wastage and weakness

While any breed can develop Cushing's disease, certain breeds are at greater risk, including all Poodle breeds, small Terriers, Dachshunds, German Shepherd Dogs, Beagles, Labradors, Boxers, and Boston Terriers.

Diagnosing Canine Cushing's Disease

Early veterinary consultation is crucial if you notice symptoms suggestive of Cushing's disease. Diagnosis can be complex because no single test definitively confirms the condition. Your vet will typically:

1. Review the dog's clinical history and perform a physical examination.
2. Measure water intake, ideally recording daily consumption as values above 100ml per kg of bodyweight over 24 hours are considered excessive.
3. Analyze urine samples to assess cortisol levels and exclude urinary tract infections.
4. Conduct multiple blood tests to rule out other diseases with similar symptoms and assess adrenal function.
5. Recommend abdominal ultrasound, if available, to evaluate adrenal glands and help distinguish between pituitary-dependent and adrenal-dependent forms.
6. In some cases, refer to a specialist for advanced imaging like CT or MRI scans to locate tumours precisely.

Gathering a urine sample on the morning of your vet appointment can aid diagnosis, and your vet can advise on the easiest methods. Although the process can be challenging, especially in multi-pet households, accurate evaluation leads to better treatment decisions.

Treatment Options and Management

Pituitary-Dependent Cushing's Disease

The primary treatment in the UK is the medication Vetoryl (trilostane), which blocks cortisol production. It is given daily and usually required lifelong. Most dogs show improvement within two weeks. Regular veterinary monitoring and blood check-ups are essential to monitor effectiveness and adjust dosage, typically at 10 days, 4 weeks, and 12 weeks after starting, then every three months.

In rare cases where dogs do not respond well, mitotane may be prescribed, which targets adrenal cells producing excess cortisol. Surgery is rarely used for pituitary tumours, reserved only for cases causing neurological signs.

Adrenal-Dependent Cushing's Disease

Management here is more complicated due to the possibility of malignant tumours. Options include surgical removal of the adrenal tumour (if no evidence of spread), medical treatment with mitotane, or symptom control using Vetoryl. Close discussion with your vet or a specialist is recommended to determine the best course based on the dog's condition.

Medication-Induced Cushing's Disease

This form often improves simply by gradual withdrawal of steroid medications under veterinary guidance to avoid withdrawal complications. Never stop medication abruptly.

Promoting Your Dog's Wellbeing

Ongoing care, including a balanced diet, maintaining a healthy weight, regular exercise, and veterinary check-ups, improves quality of life. Owners should be vigilant for changes in symptoms and communicate with their vet promptly.

If you are considering bringing a new dog into your home, always seek puppies or dogs from responsible breeders or reputable rehoming centres to ensure health and welfare from the start.

Summary

Canine Cushing's disease is a lifelong hormonal disorder more common in older dogs and certain breeds. Early recognition and veterinary diagnosis facilitate timely management, improving your dog's comfort and longevity. Treatment mainly involves medication to control cortisol levels, with ongoing monitoring essential to adapt care. With proper support, many dogs live well despite this diagnosis.