Hyperthyroidism in dogs is the presence of elevated thyroid hormone levels in a dog's body. Although hypothyroidism (low level of thyroid hormone in dogs) is a disease commonly seen, hyperthyroid disease in dogs is much less commonly diagnosed. If left untreated, it can have serious consequences for your dog's health. 

What Are Hyperthyroidism Symptoms in Dogs?

Signs of hyperthyroidism in dogs can be exhibited with elevated levels of thyroid hormone. However, the presence of symptoms can also be due to a whole host of other causes.

The most common hyperthyroidism symptoms include:

• Increased appetite.
• Increased thirst.
• Increased number of poos.
• Peeing more frequently and in larger amounts.
• A lump on the underside of the neck/enlarged thyroid gland.
• Increased heart rate.
• Weight loss.
• Personality changes.
• Vomiting and/or diarrhoea.
• Heart problems.
• Breathing changes.
• Difficulties swallowing.

In the early stages of hyperthyroid disease in dogs, no symptoms may initially be shown. This can make early detection particularly challenging. You should speak to your vet if you notice any symptoms of hyperthyroidism in your pet or if you have any concerns.

What Are the Common Causes of Hyperthyroidism in Dogs?

There are various causes of hyperthyroidism; the most common cause is a thyroid tumour. Thyroid tumours in dogs can be benign (adenoma) or malignant (carcinoma).

Benign tumours grow and produce excess thyroid hormone, and malignant tumours can spread to other parts of the body and are classed as dog thyroid cancer.

Thyroid carcinomas in dogs are the most common thyroid tumours. If a tumour is suspected, it will be assumed to be a carcinoma until proven otherwise. 

Another cause for elevated thyroid hormone levels can be dietary. Some raw-fed dogs will cause elevated levels of thyroid hormones due to thyroid glands being consumed as part of the raw diet. If this is the case, your dog's thyroid gland will not show signs of enlargement or structural changes.

Hyperthyroidism in Dogs' Diagnosis

To diagnose hyperthyroidism in dogs, your vet will first perform a full clinical examination. They'll check your pet's heart rate and feel the thyroid gland to see if there's any enlargement or irregularity to the structure. If hyperthyroidism is suspected, further testing is needed.

A blood test is the next step to diagnosis, this will be analysed to measure thyroid hormone levels such as T4, T3, Free T4 and total T4.

Sometimes, additional tests, such as a stimulation test or T3 suppression tests, are required to more accurately assess levels of thyroid hormones. It's likely that your vet will also want to do a more general blood test to check the functioning of your pet's other organs.

Your vet may recommend imaging of the area to determine if there's any spread. If thyroid cancer is suspected, your vet may recommend a fine needle aspirate (FNA) or a biopsy to determine the tumour type.

How to Treat Hyperthyroidism in Dogs

Your vet determines treatment for hyperthyroidism in pets based on the examination and your dog's thyroid hormone levels.

Common treatment options include:

• Surgery: removing the tumour or part/all of the thyroid gland is a standard approach. This option depends on the tumour's size and whether it has spread. If the tumour has invaded nearby blood vessels, complete removal may not be possible, and there's a risk of regrowth.
• Radiation therapy & chemotherapy: radiation therapy for dogs is used in treating tumours that are too large to remove or for those that have recurred after surgery.
• Radioactive Iodine: this treatment may be recommended, either alone or in combination with radiation therapy or chemotherapy, especially if surgery was unsuccessful or the tumour has returned. This treatment option depends on the stage of the cancer.
• Medication: if your pet's hyperthyroidism is caused by thyroid disease without a mass, your vet may prescribe medication to regulate thyroid hormone levels.

In some cases, ongoing medication and regular blood tests to monitor thyroid hormones may be necessary. Calcium levels must be monitored if the parathyroid glands near the thyroid are damaged or removed.

Suppose hyperthyroidism is linked to dietary factors (such as ingesting thyroid tissue from raw food). In that case, you may need to consult your vet, a nutritionist, or the diet manufacturer to address the issue and eliminate the thyroid tissue.

What is the Prognosis for a Dog with Hyperthyroidism?

The prognosis for hyperthyroidism depends on the underlying cause of the elevated thyroid hormone levels. If the cause is related to dietary factors, such as ingesting thyroid tissue, the prognosis is excellent, and the pet is likely to make a full recovery. For pets with a tumour, the prognosis varies.

The survival time is generally much longer if the tumour is completely removed and hasn't spread. However, the prognosis is poor if the tumour is inoperable or has already spread.

In cases of malignant tumours that cannot be treated effectively, palliative care may be an option to help manage your pet's quality of life. Your vet will provide a prognosis based on your pet's specific condition and circumstances.

Hyperthyroidism in dogs, though rare, is a serious condition, so it's important to be vigilant and understand how to spot the telltale signs.

Early detection is key for successful treatment, which may involve surgery, radiation therapy, medication, or dietary changes. The prognosis depends on the cause, with better outcomes for tumours that can be removed.

Regular veterinary check-ups and open communication with your vet are essential to ensure the best care for your pet.

Always consult your vet if you notice any unusual symptoms in your dog, as early intervention can help improve the overall treatment success.

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Content provided from Vetstream's Vetlexicon Canis – www.vetlexicon.com/canis

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