We tend to think about thyroid issues as being a more “cat thing”, but it’s not always the case… Because yes, dogs can certainly get nodules and abnormal growths in their thyroids. Here’s how you spot it, and what can be done about it.
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What‘s the thyroid?
The thyroid is a gland that sits in two parts either side of the trachea (windpipe) and is paired with the parathyroid glands. The thyroid predominantly produces a hormone called thyroxine, commonly referred to as T4. This hormone is very important in moderating metabolism, the rate at which the body uses energy. It influences almost all body tissues and helps to control vital functions such as the heart rate, digestive tract transit time and body temperature.
What can go wrong with the thyroid?
In animals, the common problems that are seen with the thyroid is overactivity or underactivity. Overactivity causes hyperthyroidism which is common in cats and underactivity causes hypothyroidism which is common in dogs. Unfortunately, there are also thyroid cancers seen in dogs and cats.
What kind of thyroid cancers are there in dogs?
The thyroid can become diseased with thyroid adenomas or thyroid carcinomas. Thyroid adenomas in dogs are usually small and non-functional. This means they produce no or little functional thyroid hormone. And do not have the capacity to spread elsewhere in the body as they are benign.
Thyroid carcinomas, however, are generally large in size and are either a visible lump on the neck or palpable. They are also able to infiltrate neighbouring structures such as the food pipe (oesophagus), trachea and muscles in the neck. Unfortunately, these cancers are able to metastasise; meaning they can spread around the body, commonly to local lymph nodes and the lungs, but can also go to more distant areas such as the liver. Despite these cancers being large, dogs more often either have normal or low levels of thyroxine with these types of tumours, with only about 10% of these masses having functional tissue and causing raised thyroxine levels.
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How might I know if my dog has thyroid cancer?
Clinical signs vary depending on the size of the thyroid cancer, how far it has spread (metastasised) and its ability to produce thyroxine hormone. As mentioned, a lump on a dog’s neck around the level of the thyroid hormone would be an indicator of a thyroid cancer. Dogs can also show signs of dysphagia (difficulty swallowing), dyspnoea (difficulty breathing) or even changes in the sound of their bark due to the space occupying effect of the mass.
If the thyroid cancer has spread around the body, more general signs of being unwell such as weight loss and exercise intolerance may be noted by an owner. Because thyroid cancers can destroy functional thyroid tissue, dogs may become hypothyroid with this disease, causing weight gain, lethargy and heat seeking behaviours. Equally in the few cases with hyperthyroidism signs such as weight loss, increased appetite and thirst, as well as changes in behaviour.
What kind of dogs generally get thyroid cancers?
Generally older dogs, over ten years of age are more predisposed to thyroid cancers. It is also more commonly seen in larger dogs, such as boxers and golden retrievers.
How is it diagnosed?
A variety of diagnostics are utilised during the diagnosis of the thyroid gland. Initially full bloodwork will be done including testing for thyroid hormone levels. This alone cannot diagnose a tumour, so other diagnostics are utilised such as an ultrasound to initially confirm the presence of a mass, then taking an aspirate of cells from that can be examined microscopically. Radiographs of the dog’s chest are also recommended to rule out metastasis to the lungs. And an ultrasound of the abdomen may be recommended for the same reason. Sometimes a biopsy is the only way to confirm the diagnosis. And advanced imaging such as CT may be recommended as the only way to fully assess the level of infiltration of the cancerous tissue.
What treatment is available?
Your vet may recommend any of the options of surgery, chemotherapy or radiotherapy, an advanced form of radiotherapy called Stereotactic radiosurgery (SRS), or radioactive iodine treatment. What treatment is recommended will depend on the type of tumour, the type of dog you have and the level of spread that has already occurred.
What is the prognosis?
Again, prognosis will depend on the type of tumour and the level of metastatic spread. For smaller tumours that are completely removed surgically, prognosis is excellent. For larger tumours with local spread, prognosis can be expected to be around 6-24 months, depending on the aggressiveness of treatment.
Further reading:
- Learn About Thyroid Cancer in Dogs | PetCure Oncology Peterson, M.E. (2019) The thyroid gland in animals – endocrine system, MSD Veterinary Manual. (Accessed: 14 April 2024).
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