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Hypothyroidism and Thyroiditis

What is the Thyroid Gland?                                                                                                                        

The thyroid gland produces thyroid hormone (T4) which supports a normal healthy metabolism. Thyroid hormones are needed for the normal cellular functions of the entire body.

How is Thyroid Hormone Made?                                                                                                               

The Pituitary gland produces Thyroid Stimulating Hormone (TSH). TSH ‘tells’ the thyroid gland to produce T4 (thyroid hormone). In a normal animal if the T4 concentration falls, the pituitary produces larger amounts of TSH. This stimulates the thyroid to make more T4. If the thyroid can not make T4 then the animal develops hypothyroidism.

What Causes Hypothyroidism in Salukis?                                                                                              

Lymphocytic Thyroiditis is a cause of hypothyroidism in Salukis. It is inherited, meaning it is passed down from parents to their offspring. Thyroiditis is an immune mediated disorder that starts early in life and gradually progresses. The body produces Thyroglobulin autoantibodies (TgAA). These antibodies gradually destroy the thyroid gland until it can no longer create thyroid hormone (T4). This process can take years to cause hypothyroidism. When the thyroid gland is no longer capable of producing enough hormones and the signs appear. Because the destruction of the thyroid gland takes years, signs of hypothyroidism have a gradual onset, and can be subtle. A test for these TgAA antibodies is an important part of determining if a dog is at risk for one day developing hypothyroidism. By breeding Salukis that are negative for TgAA we can continue this healthy trend in our unique breed.

Clinical Signs and Symptoms of Hypothyroidism?                                                                               

Because Thyroid hormones are needed for the normal cellular functions of the entire body deficiencies affect almost all organ systems.

Common Signs of Hypothyroidism​

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  • Weight gain (without an increase in appetite)

  • Lethargy (tiredness) and lack of desire to exercise

  • High blood cholesterol

  • Abnormal hair loss not associated with itching (most commonly along the trunk, base of tail, chest, bridge of nose)

  • Poor coat quality (dry, brittle, dull)

  • Darkening of the skin

  • Recurrent skin and ear infections

  • Slow hair regrowth after clipping  

  • Heat seeking behavior

Less Common Signs of Hypothyroidism

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  • Neurologic signs: abnormal function of nerves causing non-painful lameness, dragging of feet, lack of coordination, and a head tilt

  • Slow heart rate

  • Lack of heat periods, infertility

  • Abortion (miscarriage) 

  • Keratoconjunctivitis sicca (KCS) or dry eye due to lack of proper tear production 

  • Behavior changes (aggression, anxiety)

Testing and Monitoring Healthy Saluki                                                                                                   

There is no single easy test to diagnose hypothyroidism, but early testing, and thyroid monitoring is recommended.  Development of Lymphocytic Thyroiditis can occur at any time in a dogs life, but usually starts around 3-4 years old.

Recommended Yearly Testing on Healthy Dogs                                                                                   

Yearly  T4 and TgAA  levels are recommended as a general thyroid health screening. - T4 -  If the Tt value is within their established normal range, then most likely, the dog is not hypothyroid at this time. In our Saluki study more than half of the dogs had T4 values lower than expected.  Because normal Saluki’s often  have lower than average   T4 levels  it  is important to monitor what is normal for your dog, so you and your Veterinarian  know when, or if, it changes.  If the T4 is low, then further testing is definitely needed.  - TgAA- The test for TgAA antibodies is an important part of determining if a dog is at risk for one day developing hypothyroidism.   The TgAA test can identify dogs in the early stages of autoimmune thyroiditis long (even 3 to 5 years) before changes occur in the T4 levels and before signs of hypothyroidism occur. ​​ Saluki’s that are positive for antibodies have  a 20% chance of becoming hypothyroid.  By breeding Salukis that are negative for TgAA we prevent their offspring from developing immune mediated thyroiditis.

What are ‘Normal Thyroid Values” for Salukis?                                                                                    

Before we discuss what is abnormal in a saluki, we need to discuss what is normal. Our studies have demonstrated that: - Around 50% of healthy Salukis have lower levels of thyroid hormone (T4).  - 10% of Salukis have increased  thyroid stimulating hormone (TSH).   - Male Salukis have significantly lower T4 levels than females. ​These Salukis do not have any symptoms of hypothyroidism.  A diagnosis of hypothyroidism in Salukis should be based on two things:  Lab work results - Low T4 concentrations are the most commonly seen abnormality in dogs with hypothyroidism.    The presence of consistent signs and symptoms of Hypothyroidism.

Diagnosing Dogs with Suspected Hypothyroidism                                                                              

For any dog showing clinical signs of hypothyroidism,  or if the T4 is lower than - we recommend having your veterinarian perform a full panel of thyroid values run is highly recommended.
 

When interpreting lab work results we recommend using Sight Hound Reference Intervals.

Testing  Used To Diagnose Hypothyroidism                                                                                          

MSU Thyroid Diagnostic Panel is used to diagnose and monitor hypothyroid disease. It includes the Following:  - T4 - A baseline test which measures all of the thyroid hormone that is present in the body. T4 can be lower in normal Saluki, additional testing is recommended if the value is below 0.8 (especially if this is a new finding). - TSH- Thyroid Stimulating Hormone - If the thyroid is not able to produce enough T4,  TSH concentrations will increase as the body tries to ‘force’ the thyroid to create more. ​- Free T4-  Measures the active amount of thyroid hormone (T4)T4.  Total T4 measures ‘all of the thyroid hormone in the body’. Free T4 measures how much of that hormone is ‘working’ in the body.  - TgAA -  Antibodies against thyroglobulin (TgAA) are produced during the development of lymphocytic thyroiditis.  This test is used to identify animals at risk for becoming hypothyroid later on. Saluki’s that are positive for antibodies have  a 20% chance of becoming hypothyroid.

​NORMAL Reference Intervals for Saluki and Sighthounds                                                                

- Total T4 General Canine  1.0–4.0 µg/dL - Total T4 Sighthounds  0.5–1.7 µg/dL   - Additional Testing is Recommended for ALL animals with a T4 lower than 0.8 (MSU Diagnostic Panel) - Free T4 - 6-42 pmol/L - TSH -  0-37 mU/L - TgAA - negative

Treatment of Hypothyroidism                                                                                                   

Your veterinarian will prescribe a synthetic thyroid hormone called levothyroxine. It is usually given twice daily. This medication will need to be given for the rest of your dog’s life.   After starting medication, your veterinarian will want to see your dog in a few weeks for an additional exam and to perform blood work to make sure their levels of Thyroid Hormone have returned to Normal and that their clinical signs have resolved. Periodic exams and blood tests will be recommended for life.  The most common blood test done to monitor progress with treatment is a “Post-Pill T4.” It is recommended that the Results of the Post-Pill T4 for sighthounds be  0.5-1.7 µg/dL. ​Please note, the biggest goal of treatment is improvement of clinical signs- so doses should be adjusted if your dog is still symptomatic.

What is the prognosis for hypothyroidism?                                                                           

​With an accurate diagnosis, as well as appropriate treatment and monitoring, hypothyroidism carries a good prognosis (overall success rate).  Many of your dog’s abnormal signs will show improvement within a few weeks, although improvement in skin and haircoat may take several months.

​​​​​​References and Resources:                                                                                                                                                        

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