Recognising the symptoms of Cushing’s syndrome in dogs

The most common clinical signs seen with Cushing’s are that dogs start to drink a lot more and require more frequent visits outside to urinate.

Are you finding that your dog needs letting out into the garden much more frequently? Are you filling up the water bowl multiple times per day? Is your dog waking you through the night to urinate, or having accidents indoors when they are normally well house trained? If yes, then you are not alone. Most owners of dogs with Cushing’s report these findings.

The exact mechanism behind this is not fully understood, however it is thought that the increase in cortisol interferes with water absorption in the kidney. This means more urine is produced and subsequently your dog needs to urinate more frequently.

As your dog is urinating more, they are losing water. This is replaced by an increase in drinking and water should not be withheld from your dog.

If you are finding that your once picky dog is now eating all their food and more, or your dog has shown a change in behaviour to become more aggressive and protective around food, then you should discuss this with your vet.

Cortisol has a direct impact on the metabolism and therefore hunger of your dog. When cortisol increases, so too does appetite and this can lead to the changes described above.

There are three reasons why a dog with Cushing’s many be more prone to a urinary tract infection:

1. Excessive amounts of cortisol in the blood lower your dog’s immune system, leaving them susceptible to infection
2. The urine produced by a dog with Cushing’s is often very dilute and therefore less toxic to bacteria. They are able to reproduce more easily – leading to infection
3. As most dogs are house trained, they avoid urinating indoors where possible, and this can lead to them holding large volumes of urine in their bladders. This can lead to weakness in the bladder muscle and leave your pet prone to infection.

A one-off infection in a young dog is unlikely to be as a result of Cushing’s, however if you are visiting your vet frequently with these signs, it may lead to an increase in suspicion of Cushing’s.

An increase in appetite can cause your dog to gain weight, but your pet may physically look as though they have gained more weight than the scales show. This is due to a rounded appearance of their waist – otherwise known as a pot belly.

A pot belly is seen in dogs with Cushing’s due to a combination of factors:

1. Muscle weakness means that the abdominal muscles stretch under the weight of your dog’s internal organs
2. Of their organs, the liver becomes enlarged and heavier – increasing the size of the belly
3. Fat is moved into the belly – increasing the weight being held by the abdominal muscles
4. As mentioned under urinary tract infections, dogs with Cushing’s often hold a large volume of urine in their bladders, again adding to the weight of the abdomen and increasing the potbellied appearance

Cortisol is catabolic hormone – which means that it breaks down muscles, making them weak. An increase in cortisol can lead to an increase in muscle breakdown.

Practically for your dog, this may mean it is more difficult to stand up, jump up onto the sofa, or climb up and down the stairs.

Muscle weakness affects the entire body, including the muscles for breathing. Weakness in these muscles can lead to an increase in panting. It is also thought that cortisol may have a direct impact on the part of the brain which controls breathing.

Where Cushing’s is caused by a pituitary tumour, it is thought that lethargy may be due to increases in the hormone ACTH. Cortisol may also impact on signaling within the brain, leading to your dog sleeping more and being less willing to exercise.

Hair loss can be common in dogs with Cushing’s and you may find that your dog is losing their fur along both sides of their body, over their belly and / or along their tail.

For some dogs this hair loss can be extreme, leaving them only with fur over their head and feet. Yet for other dogs it may more subtle – with signs such as having a dull coat, hair not growing back after being clipped or blackhead formation in the armpits or groin.

In healthy dogs, the hair is grown and shed in a constant cycle. In dogs with Cushing’s this cycle slows down, or stops completely, meaning hair that falls out fails to regrow.

Skin can also become thinner as a result of excessive cortisol and when this is combined with a reduction in the function of the immune system (as mentioned in the section on urinary tract infection) then recurrent skin infections can also become a problem.