Diagnosing Hypothyroidism in Dogs: A Comprehensive Guide

Hypothyroidism is a common endocrine disorder in dogs that affects their metabolism, energy levels, and overall health. It's estimated that 1 in 200 dogs develop hypothyroidism.

Symptoms can vary from dog to dog, but common signs include weight gain, dry skin, and a dull coat. Some dogs may also experience hair loss, lethargy, and increased shedding.

A blood test is the primary diagnostic tool for hypothyroidism, measuring the levels of thyroid hormones in the blood. This test is usually performed after a veterinarian has taken a complete medical history and performed a physical examination.

The American Animal Hospital Association (AAHA) recommends a minimum of two blood tests to confirm a diagnosis of hypothyroidism, as a single test may not be accurate.

Hypothyroidism in dogs is a common endocrine disorder that affects the thyroid gland. It's often referred to as a "silent" disease because the symptoms can be subtle and may mimic normal aging in dogs.

There are two main causes of hypothyroidism in dogs: lymphocytic thyroiditis and idiopathic atrophy. Genetics play a role in lymphocytic thyroiditis, which is an autoimmune disease similar to Hashimoto's disease in humans.

Idiopathic atrophy, on the other hand, is a condition where the thyroid gland shrinks with no known cause. This can lead to a decrease in the production of thyroid hormones.

Hypothyroidism can cause a range of symptoms in dogs, including weight gain, ear infections, and hair loss. These symptoms can develop gradually, making it difficult to notice anything is wrong.

Here are some common symptoms of hypothyroidism in dogs:

In some cases, cancer can also lead to hypothyroidism in dogs, but this is rare, accounting for less than 5% of cases.

Diagnosis of hypothyroidism in dogs can be a challenge due to the many organs influenced by thyroxine and the similarity of symptoms with other skin conditions.

Cushing's disease, skin allergies, sarcoptic mange, demodectic mange, and Ringworm are just a few of the diseases that must be considered when making a diagnosis.

Additional reading: Skin Problems in Dogs with Hypothyroidism

A thorough approach is essential for an accurate diagnosis of hypothyroidism in dogs.

Anti-thyroglobulin antibodies (ATA) are found in 42 to 59% of hypothyroid dogs, which is more common than in euthyroid dogs.

A positive ATA titer may occur in euthyroid dogs, but the proportion of euthyroid dogs that ultimately develop hypothyroidism is unknown.

Approximately 20% of euthyroid dogs with thyroiditis develop some evidence of thyroid dysfunction within one year.

Measurement of ATA has been advocated for screening breeding stock, but it has yet to be proven effective in eliminating heritable forms of thyroiditis.

Anti-T3 and T4 antibodies also occur in canine thyroiditis, although they are less prevalent than ATA.

The presence of anti-thyroid antibodies increases the likelihood of hypothyroidism, especially in younger dogs and breeds with a high prevalence of hypothyroidism.

Anti-thyroid antibodies can interfere with hormone assays, leading to a spurious increase or decrease in measured hormone concentration.

Middle-aged to older dogs are typically affected by hypothyroidism, and the onset of clinical signs is gradual.

Lethargy, weight gain, cold intolerance, dermatological concerns, and neuromuscular disease are common symptoms.

Dogs may also experience laryngeal paralysis and megaoesophagus, although a causal relationship with hypothyroidism has not been established.

Clinical signs can include hair loss, scaly skin, skin infections, and lethargy.

Overweight or obese dogs are more likely to be hypothyroid, but overfeeding and lack of exercise are more common causes of obesity.

A thorough physical exam and consideration of the dog's signalment (age and breed) are essential for diagnosing hypothyroidism.

Here are some common clinical signs of hypothyroidism:

If your dog has a weight problem plus another symptom, such as chronic ear infections, hyperpigmented skin with unexplained hair loss, or a drop in energy level, it could be a sign of hypothyroidism.

High cholesterol, even after fasting for a blood test, is a common sign of hypothyroidism in dogs.

It's essential to fast your dog for at least 12 hours before a blood test to get accurate results.

Common clinical signs of hypothyroidism include:

Diagnosing hypothyroidism in dogs requires a thorough approach due to the many organs influenced by thyroxine and the similarity of symptoms to other skin conditions. Multiple diseases need to be considered, including Cushing's disease, skin allergies, sarcoptic mange, demodectic mange, and Ringworm.

A correct diagnosis of hypothyroidism is crucial, and a veterinarian will typically follow a tenet's approach to ensure accuracy and avoid overlooking other diseases that may be present in aging pets. This includes considering the dog's clinical status and overall health.

If an initial TT4 screening shows low T4 concentration, further blood tests are usually recommended, but these can be expensive. A veterinarian may propose three options: monitoring the dog and repeating the basic blood panel, running additional diagnostic testing, or beginning a month-long trial on thyroid medication.

Measuring concurrent TSH is crucial in diagnosing hypothyroidism in dogs.

TSH can be within the reference range in 20-40% of dogs with hypothyroidism, which can make interpretation challenging. This is because the body's response to low T4 levels can weaken over time, making it harder to detect.

You may find a normal T4 with an increased TSH, which could indicate recovery from a recent illness or an early stage of the disease where the body is still maintaining normal T4 levels.

Here are some possible scenarios to consider:

In either case, it's essential to monitor these dogs and retest them 1-3 months later to confirm the diagnosis.

After an initial TT4 screening, you'll likely have some decisions to make about what to do next. The gold standard is further blood tests, but these can be expensive.

In my experience, three options are usually presented to dog owners. Here are the details:

This third option is often the most viable choice for owners with financial limitations, but it can lead to over-diagnosis. Sometimes, dogs feel and do better on the medication, even if they didn't have a primary thyroid problem.

This is because many diseases and conditions can mimic hypothyroidism, and some clinical signs can improve after administration of exogenous supplemented thyroid hormone, as the Merck Veterinary Manual explains.

In fact, I've seen many cases where dog owners try thyroid medication for a month, and the dog returns for a follow-up with improved symptoms. The repeat T4 level often comes back higher, but not "crazy high." In these cases, the dog will usually stay on thyroid medication for life, as long as their veterinarian monitors their T4 levels every six to twelve months.

Rarely, I do see cases of toxicosis in dogs from overdosing on thyroid medication, which can cause symptoms like hyperactive behavior, increased thirst and urination, and heart issues.

Middle-aged to older dogs are typically affected by hypothyroidism, with the onset of clinical signs being gradual. The condition can occur at any age, but it tends to be a problem that affects middle-aged and older dogs, especially larger breeds.

Several canine breeds are prone to getting hypothyroidism, including Chow, Great Dane, Irish Wolfhound, Cocker Spaniel, Golden Retriever, Poodle, English Bulldog, Schnauzer, Boxer, Dachshund, German Shepherd, Doberman Pinscher, Borzoi, Irish Setter, Old English Sheepdog, Miniature Schnauzer, and Airedale Terrier.

Females and males get hypothyroidism at about the same frequency, and neutered pets might be at higher risk of the condition.

There is no definitive blood sample that can diagnose hypothyroidism in dogs. Many factors affect the level of thyroxine in the bloodstream, including normal fluctuations.

A routine blood sample typically includes an add-on test called a T4 test. A normal T4 test result suggests that a dog probably does not have hypothyroidism.

However, a low T4 test result does not necessarily mean that a dog has hypothyroidism. It could be due to a non-thyroidal illness (NTI) caused by factors such as medications or diseases like Cushing’s disease.

To differentiate between NTI and true hypothyroidism, a free T4 test by equilibrium dialysis (ED) is used. If the free T4 level is low, and the signalment, history, and physical exam are consistent with hypothyroidism, a diagnosis is made.

The TT4 screening test is a good place to start, but it's essential to understand that it's only a screening test. If the TT4 comes back in the upper 50% of the reference range, hypothyroidism can be ruled out.

Recommended read: Why Does My Male Dog Lick My Female Dogs Ear

Treatment of hypothyroidism in dogs typically involves administering levothyroxine, a synthetic hormone that replaces the missing thyroid hormone.

Levothyroxine is usually given twice daily, but once a dog is stable, they can be transitioned to a once daily regime. It's essential to note that absorption of the drug may be affected by food.

Clinical response to treatment should be evaluated by measuring T4 and TSH 4-6 hours post administration of levothyroxine, and 6-8 weeks after starting treatment.

A thyroid level needs to be checked initially at 1 month to make minor adjustments, and then every 6 months to refine the dose.

Medication is given every 12 hours, and the thyroid pill should be given 4-6 hours prior to the recheck blood test.

It's crucial to use the name brand version of levothyroxine, such as Soloxine or Synthroid, as generic versions may not be absorbed as well.

Some dogs may experience an increase in energy level within a few days of starting treatment, while skin problems and ear infections may take four to eight weeks to improve.

With treatment, most dogs develop an increase in appetite and weight loss, which is a beautiful thing to see.

Diagnosing hypothyroidism in dogs can be a challenging task, but with the right approach, it's possible to get to the bottom of the issue.

Veterinary professionals play a crucial role in diagnosing hypothyroidism in dogs. They have access to a Veterinary Professionals Referral Feedback Form that helps them track and evaluate cases.

For some patients, diagnosis can be straightforward. However, in others, it can be more challenging due to the complexity of the disease.

Veterinary professionals can refer cases to CPD at North Downs for further evaluation and guidance. This can be especially helpful when dealing with difficult cases.

The most common causes of hypothyroidism in dogs are lymphocytic thyroiditis and idiopathic thyroid atrophy. These conditions can lead to a range of symptoms, including weight gain and skin problems.

Veterinary professionals can use the Refer A Case feature to send cases to specialists for further evaluation. This can help ensure that dogs receive the best possible care.

If you've referred a case to a specialist, you can keep track of your referral history using the My Referral History feature. This can be a useful tool for monitoring the progress of your patients.

Hypothyroidism is a common endocrine disease in dogs, and it's essential to take a comprehensive approach to diagnosis and treatment. By working with veterinary professionals and using the right tools and resources, you can help ensure the best possible outcome for your furry friends.

Diagnosing hypothyroidism in dogs can be a challenging process, but it's not impossible.

Samuel, a nine-year-old Siberian Husky, is a great example of this. He was gaining weight and developing hot spots along his back, but initial blood tests were normal.

His symptoms only progressed with more lethargy, skin problems, and continued weight gain despite a strict diet.

A full thyroid panel sent to a reference lab revealed a low normal TT4, low free T4, and high TSH – a classic panel for true hypothyroidism.

This case highlights the importance of not giving up on testing if symptoms persist.

The endocrine system plays a crucial role in regulating various bodily functions, including metabolism and growth. Hypothyroidism, a condition where the thyroid gland doesn't produce enough thyroxine, can have a significant impact on these processes.

Hypothyroidism is often associated with other health issues, such as sugar diabetes and Addison's disease. This is because the thyroid gland's hormones, like thyroxine, affect the metabolism of every cell in the body.