Thyroid disease in canines

December 20th, 2013
Houndstooth - Thyroid disease in canines

Is Rover suddenly losing weight or piling on the kilos? Is he lethargic or having a ‘bad fur day’? Thyroid disease could be the culprit, writes Laura Greaves.

After a rough start to life, Ted, the rescued Golden Retriever, has always been a ‘serious’ pooch. But, when he started to gain weight and become lethargic, owner Kerry Northey became worried.

“Ted came to us eight years ago, when he was about two. His owner had been forced to surrender him and eight other dogs after mistreating them,” says Northey, who lives in the Adelaide Hills. “I think he had spent most of his time in a cage or some very confined space.

“He was undernourished and afraid of loud noises. I suspect he had been hit quite often, as just raising a hand would make him cower with fear.”

Ted also seemed to be agoraphobic, refusing to step beyond Northey’s front gate despite having an 18-acre property to roam. “When he is away from our property he is very tense and nervous and has only one aim – to get back home,” she says.

Over time, and with patience and loving care, Ted was able to conquer many of his issues. He blossomed into a friendly, energetic dog that loves car rides and has a big appetite.

That’s why a sudden change in his demeanour two years ago immediately rang alarm bells. “He seemed to become lethargic, was putting on weight and did not seem very happy. We tried changing his diet but that didn’t do anything,” says Northey.

“Ted’s face and eyes show a lot of expression and you can really tell if he’s not well.”

So she whisked her canine companion off to the vet, where a surprising diagnosis was delivered: Ted has thyroid disease.

What is thyroid disease?

The thyroid is an endocrine gland found in the neck. It secretes hormones called thyroxine and triiodothyronine, which regulate the metabolism and affect the growth rate and function of many other systems in the body. Their production is controlled by another hormone, known as TSH, which is produced in the pituitary gland.

As in humans, there are two types of thyroid disease that can affect dogs. Hypothyroidism means the thyroid is not producing enough thyroxine and triiodothyronine, while hyperthyroidism means the gland is making too much of these hormones.

Both conditions are fortunately relatively rare in dogs, but hypothyroidism occurs far more frequently than hyperthyroidism, according to Brisbane veterinarian Audrey Harvey.

“Hyperthyroidism isn’t common in dogs. Hypothyroidism tends to affect middle-aged and elderly dogs,” she explains. “There is also thought to be some breed predisposition for hypothyroidism, with the Doberman, Irish Terrier and Golden Retriever more likely to be affected.”

While a thyroid carcinoma, or tumour, is the most likely cause of hyperthyroidism, the causes of hypothyroidism are a little more difficult to pinpoint.

“Hypothyroidism is thought to be due to the immune system’s destruction of the thyroid gland or natural atrophy, or wasting, of the gland,” says Dr Harvey. “Having said that, this wasting may be the end stage of previously undiagnosed autoimmune disease.”

In humans, iodine deficiency and severe stress are also thought to contribute to hypothyroidism; dogs can suffer from both of these conditions, too.

Spot the signs

Thyroid disease in dogs can be difficult to spot, as the symptoms can be vague and may be attributed to the normal ageing process. The symptoms of hyperthyroidism include weight loss despite an increased appetite, and sometimes increased thirst and urination.

Most dogs suffering from hypothyroidism display skin problems such as dry coat, hair loss and secondary bacterial or fungal infections. As Ted discovered, weight gain and lethargy are also common symptoms.

“Thickening of the tissues of the face can lead to a sad or ‘tragic’ appearance. There may also be anaemia (deficiency in the number or quality of red blood cells), heart disease and neurological symptoms such as facial paralysis or abnormal gait,” explains Dr Harvey.

Making thyroid disease even tougher to diagnose is the fact that these symptoms may also be present in a number of other conditions, including kidney or liver disease, skin allergies or infections, pinched nerves, intervertebral disc disease and other hormonal diseases such as Cushing’s syndrome.

The good news is that when thyroid disease is suspected, blood tests can confirm the diagnosis quite quickly. Dogs with hyperthyroidism will show increased levels of thyroxine in the blood.

But testing for hypothyroidism isn’t quite as straightforward. “Vets can measure a dog’s levels of triiodothyronine, but they can appear normal even in hypothyroid dogs, so we can’t rely on that 100 per cent,” Dr Harvey says.

“Low thyroxine levels can also be associated with some medications and some non-thyroid illnesses. And for some breeds, particularly sight hounds such as Greyhounds, a lower thyroxine level can be normal.

“Sometimes it’s worth looking at a dog’s age and clinical symptoms and trying a trial of medication – seeing if the dog’s skin and demeanour improves on Thyroxine.”

Fortunately for Ted, his diagnosis was able to be quickly confirmed. “When he was examined by our vet, she suspected a thyroid problem and immediately took a blood sample. The results were back within a couple of days and treatment for hypothyroidism commenced as soon as the diagnosis was confirmed,” says Northey.

“I knew nothing at all about hypothyroidism at that point, except that I thought it was a human problem.”

Bright future

Happily, the outlook for dogs with either type of thyroid disease is largely positive. Hyperthyroidism is best treated with either radiation therapy or surgical removal of the tumour. Dogs that undergo surgery for the condition have an expected survival rate of more than three years.

While hypothyroidism can’t be completely cured – because the damaged thyroid gland cannot regenerate – most dogs do well on lifetime supplements of Thyroxine, a synthetic version of the thyroid hormone. “Hypothyroid dogs do well on long term medication with regular blood work to make sure thyroid hormones are within normal limits,” Dr Harvey explains.

Kerry Northey was understandably concerned when Ted was diagnosed with hypothyroidism, but has been encouraged by the changes in her pooch since he began treatment.

“We were concerned for Ted, but also optimistic that the problem could be managed. He became more energetic after starting on his medication and his weight dropped a little as well,” she says. “He hasn’t exactly become a puppy again, but he certainly seems a lot happier.”

What’s the alternative?

Many owners of dogs with hypothyroidism are concerned that their four-legged friends will have to take the synthetic thyroid hormone Thyroxine daily for the rest of their lives.

“The thought of Ted having to be on a drug like Thyroxine for the rest of his life was a bit of a concern,” says Northey. “We would love to find an effective, more natural treatment for him if we could.”

But is there a natural alternative? Dr Harvey says surgery or radiation remain the best treatment options for hyperthyroidism, and non-medical treatments are not appropriate. “Early removal of the carcinoma can prevent spread to other organs, in particular the lungs,” she explains.

Natural treatment of hypothyroidism may be possible, but she also advises caution here. “There has been some talk of treating hypothyroid dogs with dried thyroid glands from pigs or cattle, but there is no guarantee of quality control with respect to the amount of active ingredient,” says Dr Harvey.

“You don’t know how much hormone your dog is getting each time you dose him.”

Always consult your veterinarian before beginning any treatment.

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