Cushing’s syndrome in gundogs – what is it and how do you treat it?

Question: “My elderly chocolate labrador has just been diagnosed with Cushing’s syndrome. I confess to having a bit of ‘red mist’ when the vet discussed it with me. Can you help with my confusion?” – F. Hoyle, Poole

Do not fret, you are not alone! I always found it useful to hand a 10-page booklet, which describes Cushing’s syndrome, to each and every client whose dog was diagnosed. It is complicated. Let’s begin with the history.

Cushing’s syndrome

Harvey Williams Cushing (1869-1939), the youngest of 10 children, born in Cleveland, Ohio, was a pioneer of brain surgery, a neurosurgeon, pathologist and writer. His many remarkable claims to fame include improving the survival of patients after complicated brain surgery, using X-rays to diagnose brain tumours, assisting in developing the Bovie electrocautery tool (with William T Bovie, a physicist), and employing electromagnets to remove metallic shrapnel from the brain of wounded soldiers during World War I.

He also designed the Cushing forceps and the Cushing ventricular cannula; the former is used to grasp the thick tissues of the scalp during brain surgery and the latter is excellent for entering the brain ventricles and draining cerebrospinal fluid. As you do.

But he will be best remembered for his discovery, in 1912, of an endocrinological condition, caused by a malfunction of the pituitary gland that he called ‘polyglandular syndrome’. Now generally referred to as Cushing’s syndrome or hyperadrenocorticism, this is a relatively common disease that affects humans and dogs. It occurs as a result of the excessive production (or administration) of glucocorticoid steroid from the adrenal glands.

This can be due to tumours in the pituitary gland of the brain instructing the adrenals to produce more hormone or because of tumours in the adrenal glands themselves. Pituitary-dependent hyperadrenocorticism is more often seen in small breeds, such as the miniature poodle, dachshund, Yorkshire terrier, pomeranian and bichon frise while large breeds are over represented in the adrenal type.

What do you see?

Cushing’s syndrome is chronic in nature and the clinical signs develop over months or even years, making diagnosis in the early stages tricky. Glucocorticoid steroids have profound effects on carbohydrate, fat and protein metabolism, and are also responsible for modifying the immune response and inflammation.

When present in the body in excess they affect liver function, reduce muscle mass (these are not anabolic steroids, remember), diminish bone density, cause loss of protein from the skin, leaving it thin and prone to infection and there is a cessation of hair growth. They also create measurable changes in the blood, and affect the kidneys, the immune system and the genital system. 

How is it diagnosed?

The clinical signs put Cushing’s syndrome in the frame but it can be confirmed by observing biochemical, blood, urine and hormone changes. Cholesterol and liver enzymes are raised. Haematology demonstrates a reduction in eosinophils and lymphocytes and an increase in neutrophils. Urine is dilute and often contains a protein sediment. Despite all this, dynamic adrenal hormone assays are required, as basal hormone levels are often normal.

Two tests are used. The ACTH stimulation test measures cortisol before and after chemical stimulation of the adrenal glands; affected dogs usually show an exaggerated response. The low-dose dexamethasone suppression test involves administering steroid, which should suppress steroid production. When it fails to do so, Cushing’s is likely. Radiology, ultrasound, CT and MRI scans can also be used to assess for changes in organs and tumour size and location.

Diagnosis is not easy but excessive thirst and urine production is a symptom

The good and the bad

The good news is that treatment, usually in the form of daily capsules, is available and most dogs then have an acceptable quality of life. The bad news is that treatment is relatively expensive, especially since it must be ongoing, and around 10% of patients have malignant adrenal tumours, which fail to respond to treatment and can metastasize. 

I hope that helps and that your bitch is one of the 90%. 

Symptoms are vague but include:

• Excessive thirst and urine production
• Increased appetite
• A classic ‘pot belly’
• Lethargy
  
• Bilaterally symmetrical hair loss (which is not itchy)
  
• Lightening of hair colour
  
• Deposition of calcium in the skin
  
• Liver enlargement (which can sometimes be palpated)
  
• Testicular atrophy
  
• Anoestrus in entire bitches
  
• Thin skin, which is easily bruised and has visible superficial veins
  
• Muscle weakness
  
• Increased risk of pulmonary thromboembolism

Symptoms can include lethargy and muscle weakness