Hypothyroidism in the Cavalier King Charles Spaniel

Hypothyroidism is a genetic auto-immune disorder (lymphocytic thyroiditis) in the Cavalier King Charles spaniel which destroys the thyroid gland.  It is not life-threatening by itself, but it diminishes the Cavalier's quality of life.  It cannot be cured.  It also may complicate the care of Cavaliers which suffer from mitral valve disease (MVD).

The thyroid gland produces hormones which maintain the dog's metabolic rate -- the speed at which the dog converts nutritional energy into fuel for the body.  When the thyroid deteriorates, it begins to produce insufficient quantities of the thyroid hormones.  Then the body's cells are unable to convert nutrient energy into energy fuel as quickly as normal.

Up to 80% of all hypothyroidism in canines is due to autoimmune (lymphocytic) thyroiditis, by which T-lymphocytes destroy the thyroid gland.

Symptoms

It is most unfortunate that by the time most clinical signs of hypothyroidism appear, as much as 75% of the dog's thyroid gland may have been irreversibly destroyed.

The result causes physical changes in the Cavalier, including weight gain without any change in diet, skin infections, hair loss, temperament changes, lethargy, mental dullness, joint disease, and ligament damage. The Animal Behavior Clinic at Tufts Cummings School of Veterinary Medicine is studying the relationship between some dogs' aggression towards human family members and hypothyroidism.  See Current Research below.

Diagnosis

Early diagnosis from classic symptoms is extremely difficult because so much damage to the gland already would have occurred before clinical signs normally appear.  Also, a definitive diagnosis can be very difficult because reduced thyroid function can produce any of a number of symptoms which may mimic those of other causes.

Therefore, owners -- especially breeders -- should have a complete baseline thyroid antibody profile of their Cavalier conducted before any symptoms appear, followed by annual profiles thereafter. Thyroid testing for genetic screening purposes should start after the Cavalier has reached its sexual maturity, and females should not be tested for screening until they are between their first and second heats.

A complete thyroid antibody profile includes levels of T3AA (the active form of the hormone), T4AA (the inactive form created to circulate in the bloodstream), and serum TgAA, and not just freeT4, and administering the thyroid stimulating hormone (TSH) response test. It is reported that the presence of elevated TgAA levels usually confirms thyroiditis.

Treatment

Veterinarians treat hypothyroidism by prescribing a supplemental thyroid hormone -- usually thyroxine -- which must be administered to the Cavalier daily for the rest of its life. Once the supplemental hormone has stabilized the thyroid- hormone levels within a normal range, the dog should be examined at least every six months.

Breeders' Responsibilities