Project Hope and Hypothyroidism

Hope after successful treatment for hypothyroidism

Project Hope

New fund dedicated to detecting hypothyroidism in rescue dogs

To donate to Project Hope, just go to the donation form (Click here to donate to NGWPR) and indicate that your donation is for “Project Hope.”

Canine Hypothyroidism: Anything New?

Robin K. Nelson, DVM

Background

Hypothyroidism is arguably the most commonly diagnosed endocrine disease in dogs. The true incidence isn’t known. Confusion and inconsistencies make it difficult to establish a definitive diagnosis, so canine hypothyroidism tends to be one of the most over-diagnosed and therefore over-treated diseases in the dog. The term hypothyroidism needs to be reserved for the end stages of thyroid disease when the dog’s thyroid gland is proven to no longer produce sufficient hormones to sustain clinical health.

What is the thyroid gland and what does it do?

The thyroid gland is a small gland located in the neck region on both sides of the trachea or windpipe. It produces two hormones. Thyroxine (T4) is the protein-bound reservoir hormone that maintains a steady concentration of free hormone. Triiodothyronine (T3) is the unbound hormone which is able to penetrate cell membranes, bind to receptors, and result in biologic activity. These two hormones are responsible for metabolism (the process of turning food into fuel) at the cell level. Thyroid hormones are involved in a wide variety of metabolic processes so virtually every organ in the body is affected when thyroid hormone is low. Hypothyroidism can be life-altering, but typically not life-threatening. Low thyroid hormone levels result in a constellation of clinical signs and laboratory abnormalities. Multiple hormone tests are required to make a diagnosis. Once the diagnosis is confirmed, it is fairly inexpensive and easy to provide life-long treatment.

What causes hypothyroidism in dogs?

Canine hypothyroidism occurs in young to middle-aged dogs. Large breed dogs have an earlier onset of development than small breed dogs and dogs with autoimmune disease tend to develop hypothyroidism at a younger age. 90- 95% of cases of canine hypothyroidism are primary and due to acquired immune-mediated destruction of the thyroid gland or idiopathic atrophy of the thyroid gland. Autoimmune thyroiditis, the heritable disease, is characterized histologically (under the microscope) by diffuse infiltration of lymphocytes, plasma cells, and macrophages in the thyroid gland. Antibodies interact with the follicular colloid or thyroglobulin antigens activate cell-mediated toxicity causing a progressive destruction of hormone-producing follicles and a secondary fibrosis. This process can eventually lead to failure of thyroid hormone production. No sex predisposition has been recognized regarding canine hypothyroidism. Idiopathically reduced thyroid function rarely occurs. Its cause is unknown, with no suspicion this is a heritable trait. The functional thyroid gland tissue is replaced by fat, therefore smaller amounts of thyroid tissue remains to produce thyroid hormone. There are no autoantibodies destroying the thyroid gland (TGAA NEG). Secondary forms of hypothyroidism include TSH deficiency, pituitary neoplasia, and Cystic Rathke’s pouch. Congenital cases have also been reported in dogs.

Signs and Symptoms of Hypothyroidism

Symptoms of canine hypothyroidism are often insidious and nonspecific. They can mimic other diseases leading to an incorrect diagnosis. Common clinical signs include lethargy, weight gain or obesity, exercise intolerance, and lack of desire to work or play. Chronic, recurring skin conditions such as seborrhea, pyoderma (skin infection), alopecia (hair loss often involving tail or collar region), puppy-like coats, or failure of hair to regrow after clipping are common. Hypothyroid dogs may present with chronic otitis (ear infection) or with lipid deposits in the corneas or dry eyes (keratoconjunctivitis sicca). Hypothyroid dogs may have irregular or absent estrus cycles, low libido, infertility, and litters with low birth weight puppies. Without adequate thyroid hormone, nerves cannot conduct electrical impulses normally. Neurological signs such as general weakness, poor coordination, seizures, or even unexplained, non-painful lameness can suggest hypothyroidism. Focal nerve problems associated with hypothyroidism include facial paralysis presenting clinically as a droopy eye or lip and vestibular disease, a sudden-onset disorder where the dog presents clinically with a head tilt, bizarre eye motion, and balance disruption.

Hope before treatment
A rare syndrome int eh extreme expression of hypothyroidism is myxedema coma

Some dogs show few, if any, signs of hypothyroidism other than behavioral problems

What happens to people with hypothyroidism?

In human medicine, a wide variety of behavioral symptoms have been reported in hypothyroid patients including: reduced cognitive function and concentration, impaired short-term memory, visual and auditory hallucinations, and fear ranging from mild anxiety to frank paranoia. Mood swings and aggression have also been reported in hypothyroid human patients.

More signs and symptoms

These dogs may even be underweight and hyperactive not the typical lethargic and obese. Some dogs present with a sudden onset of aggression-usually owner directed or intraspecific (other dogs). Canine hypothyroidism has been confirmed as an underlying condition in some of these aggressive dogs. Dogs that are fearful and show nervousness early lead behaviorists to suggest anticipatory fear and anxiety leads to the aggression placing less emphasis on the thyroid disease. More research needs to be done to pursue aggressive behavior in dogs and underlying hypothyroidism.

The most important diagnostic pointer for episodic dyscontrol is the lack of provocation to justify this type of behavior.

During the unpredictable, unprovoked aggression episodes in dogs, the dogs’ eyes are often black and glazed. The speed at which a dog gets out of control is frightening. The dog may not respond to his name or any command, seemingly intent on getting to the face or neck of the perceived target. Episodic dyscontrol or “rage syndrome” is well documented in English Springer Spaniels and can be traced back to a winner at the Westminster Kennel Club dog show who went on to become a top stud (Popular sire effect) supporting possible genetic factors. Other affected breeds include Cocker Spaniels, Border Collies, Rottweilers, and Bernese Mountain Dogs, to name a few. Many dogs display first symptoms of aggression on or around one of the critical learning periods identified in dogs. The genetics of the breed and of the parents in particular, play an important role in how sociable, playful, fearful, excitable, or domineering a puppy becomes. Puppies under three months of age are still developing their social skills and many problem behaviors do not begin to emerge until sexual or social maturity. When a dog is diagnosed with episodic dyscontrol, the condition is rarely treatable, even if an underlying thyroid condition is addressed. There have been minor successes treating individuals with phenobarbital (anti-seizure) medication, but because of the nature of the disorder and its unpredictable violence, often the recommendation is humane euthanasia. The stress of what is happening, the risks and dangers to family and other dogs, friends, neighbors, all need to be considered. Overall quality of life and the hope of or odds of a turn-around are dismal. Attacks cannot be prevented with training because this is a problem the dog cannot consciously control. The attacks often occur without apparent cause although some dogs may seem to have “triggers.” Some dogs show few, if any, signs of hypothyroidism other than behavioral problems.

OFA Rank and Thyroid

GERMAN WIREHAIRED POINTERS showing clinical signs suggesting thyroid disease or unexplained behavior or aggression should be tested for hypothyroidism

Testing for Hypothyroidism

State-of-the-art assay technology is constantly being refined to determine a correct OFA thyroid classification. Currently, OFA Thyroid Profiles include:

  1. Serum Total thyroxine or TT4

There are currently THREE MAIN INDICES that determine the OFA Thyroid Classification:

1. Free T4

Alternative Explanations for decreases in thyroid laboratory values

Infectious, endocrinologic, and cancerous illnesses can all cause low thyroid values

Treatment is usually simple with medication

Treatment for Hypothyroidism

Once a diagnosis has been confirmed, treatment for canine hypothyroidism is fairly simple and inexpensive with daily synthetic thyroid hormone replacement. Levothyroxine is the only hormone that appears necessary for treatment. Studies have shown most dogs can be regulated with once-daily levothyroxine administered on an empty stomach usually initiated at .02mg/kg every 24 hours. In clinical practice, some dogs seem to respond better to twice daily medication, so it is still an option. The bioavailability of thyroxine can range from 13–87% in the same dog from day to day. Most dogs show clinical improvement within the first 1–2 weeks of therapy with increased and more normal activity and improved attitude. Cutaneous manifestations of hypothyroidism may take several weeks to months to resolve. After four weeks of supplemental therapy, blood is collected 4–6 hours post-pill for T4 measurement. The post-pill T4 should be at the upper end of the reference range or slightly above. If a dog has a “questionable diagnosis” and a trial with T4 supplementation is suggested because of a strong clinical presentation consistent with hypothyroidism and non-thyroidal illness has been ruled out, an entire “profile” should be run. An objective case review should be conducted after 6–8 weeks of trial therapy for evidence of clinical improvement. Therapy should be discontinued if clinical signs and thyroid function numbers don’t support the diagnosis. Therapeutic monitoring during treatment is lifelong.

TAKE HOME POINTS for GWP OWNERS:

  • With your veterinarian’s help, learn to read and understand your dog’s OFA Thyroid Profile. Check for TGAA- if present, results suggest thyroid pathology- usually autoimmune thyroiditis, but in older patients, possible thyroid neoplasia (cancer). The absence of TGAA doesn’t exclude the possibility of thyroid dysfunction, but it’s less likely. The OFA Thyroid Profile will help identify dogs that are phenotypically normal for breeding programs. An OFA number is issued to all dogs found to be normal at 12 months of age, but dogs in a breeding program should be re-examined at 2, 3, 4, (6 and 8) years of age. Because of the variable onset of the presence of thyroid autoantibodies, periodic testing is necessary. The majority of affected dogs will have autoantibodies by 4 years of age. ***All data whether normal or abnormal should be submitted to OFA for completeness. A GWP must be 2 years of age for the thyroid profile to qualify under current GWPCA CHIC requirements.
  • Canine hypothyroidism is heritable, so knowing the status of a dog and the status of the dog’s lineage allows breeders to decide which matings are most appropriate for reducing the incidence of autoimmune thyroiditis in GWP offspring. ***Laboratory and pedigree analyses of affected families show a progressive earlier age of onset of thyroiditis and clinical signs of dysfunction, as well as an increased portion of affected vs normal offspring in successive litters.
  • Breeding normal testing dogs that have come from litters which have mostly tested normal is recommended. ***Always retest equivocal results. Testing is not simple or perfect. Discordant test results are common and retesting can be required
  • Ruling out hypothyroidism as a contributing factor to aggression, “irritability”, and abnormal behavior is valuable.
  • It would be interesting to analyze our GWP data checking trends in our TT4, fT4, numbers as a “group.”

References:

  1. Brunette, David. Canine Hypothyroidism. Chicago Vet 2019
  2. Hanseltine, Johanna. Canine Hypothyroidism: Diagnosis and Treatment. TVP March/April 2019
  3. Dodman, NH, Miczek, KA, Knowles, K, Thelhammer, JG, Shuster, L. Phenobarbital-responsive episodic dyscontrol (rage) in dogs. JAVMA Vol 201 No 10 Nov 15 1992 1580–3
  4. Aronson, LP, Dodds, W. J. The Effect of Hypothyroid Function on Canine Behavior. Pet Shrink 2008
  5. Landsberg, GM. Is It Medical or Is It Behavioral? Companion Animal Behavior Therapy Study Group 2008
  6. Peterson, M. Hypothyroidism in Animals. Merck Manual 2019
  7. Leviton, D M. Canine Hypothyroidism — Are You Over Treating? Atlantic Coast Veterinary Conference 2016
  8. Horowitz, D, Lansbury, G. Puppy Behavior and Training- Socialization and Fear Prevention. Behavior Pet Services
  9. Shell, L, Rothrock, K. Hypothyroidism, Acquired. Vincyclopedia of Diseases 2018
  10. Please refer to Dr Sharon Albright’s article Spring 2020 Wire~News page 17 for the latest research regarding new test method development for Canine Hypothyroidism.

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National GWP Rescue is a nationwide rescue program whose volunteers work tirelessly to provide funding, foster homes, medical care and training for GWPs found in shelters, animal control facilities and to those GWPs whose current owners are unable to provide a suitable situation.

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We believe that the more we educate people the more likely we are to accomplish our mission of matching homeless GWPs with loving owners.