Thyroid Disorders

THYROID DISORDERS IN THE MUDI


HYPERTHYROIDISM (HTO) Overactive Thyroid

Hyperthyroidism is rather rare in dogs and in the Mudi. HTO is caused by excess of the thyroid hormones, T3 and T4. Signs include weight loss, increased appetite, excitability, increase in thirst and urination, vomiting, diarrhea, and increased heart rate, all of which reflect an increased metabolic rate. When HTO does occur in dogs, the most likely cause is malignant cancer of the thyroid gland (thyroid carcinoma). Medications may improve the symptoms, but will not treat an underlying tumor. Because hyperthyroidism is almost always associated with thyroid cancer, the long term prognosis is usually poor.

HYPOTHYROIDISM (HTU) Underactive Thyroid

Hypothyroidism is the most commonly diagnosed thyroid disease in the Mudi and in dogs. More than fourteen Mudis have been confirmed to be affected, with all having connections to parents or grandparents of other affected Mudis in their 3-5th generations, indicating a strong genetic inheritance pattern. Some have an HTU affected relative in their 5 generation pedigree as well.

Hypothyroidism occurs when the thyroid is not secreting enough thyroid hormones, causing your dog’s metabolism to slow. It is usually caused by inflammation or shrinkage of the thyroid gland, with a very high number of cases caused by destruction of the thyroid gland itself. It is considered to be an immune mediated disorder as research has shown that its primary cause is lymphocytic thyroiditis, an autoimmune disease that causes inflammation and destruction of the thyroid gland. Basically, the body’s immune system mistakes the thyroid gland as a foreign body and starts to attack it. Most of the time, lymphocytic thyroiditis goes unnoticed in dogs until the symptoms of hypothyroidism appear.

- HTU occurs equally in both males and females, however spayed females may have a higher risk than neutered males

- HTU is most common in dogs 4 to 10 years old

- HTU usually affects mid- to large-size breeds

- Blood tests can confirm a suspected diagnosis of hypothyroidism

- HTU is a lifelong disease as the thyroid gland cannot regenerate or repair damage

- Hypothyroidism is genetic and highly inheritable, therefore breeding dogs with the disease is not recommended; the genetic basis of the disease is complex and still being investigated

- Owners of breeding dogs are recommended to test for HTO every year, with no more than two years between tests; until 10 years of age

Treatment involves increasing or replacing the missing thyroid hormone, which in dogs is most often Thyroxine (T4). Hypothyroidism treatment will be necessary throughout the entire lifetime of the dog.

A deficiency of thyroid hormones affects the function of all organ systems, causing highly variable symptoms, these are the most common signs:
  • Lethargy
  • Exercise intolerance (inability or unwillingness)
  • Mental dullness
  • Weight gain without an increase in appetite
  • Obesity
  • Cold intolerance, seeking of heat sources
  • Changes in fur: hair thinning; balding in patches - usually bilaterally symmetric; dry, dull, lusterless fur with excessive shedding, delayed regrowth
  • Changes in skin: particularly noticeable on the face; increased dark pigmentation in the skin; sores, scabs and repeated superficial skin infections that don’t clear up; scaling; seborrhea
  • Reproductive disturbances in intact dogs: in males - lack of interest, small testicles, low sperm count or infertility; in females - irregular or lack of heat cycles, infertility, miscarriage of pregnancy, or poor litter survival
  • Slow heart rate
  • Abnormal function of nerves causing non-painful lameness, dragging of feet, lack of coordination, and head tilt
  • Drooping of upper eyelids
  • Non pruritic (not itchy) alopecia (baldness) over the trunk or areas of wear
  • Ear or toenail infections

Some medical conditions Hypothyroidism can cause:
  • Megaesophagus (enlarged esophagus)
  • Vestibular dysfunction (severe dizziness)
  • Facial nerve paralysis
  • Paralysis of the larynx
  • Atherosclerosis
  • High blood cholesterol
  • Fat deposits in the corneas of the eyes
  • Keratoconjunctivitis sicca (KCS) or dry eye due to lack of proper tear production which can cause corneal ulcers

A deeper study of hypothyroidism will be covered in a future Mudi Directions post.

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