The most common hormonal disorder affecting Beagles is Hypothyroidism which results from a deficiency of thyroid hormone. The cause of canine hypothyroidism usually stems from the destruction of the thyroid gland due to atrophy, cancer, or from an immune-mediated process called lymphocytic thyroiditis (an inflammation of the thyroid gland which involves lymphocytes). The development of lymphocytic thyroiditis in a host is believed to be caused by his genetic makeup.
The clinical signs of hypothyroidism will most usually appear around 2 to 6 years of age. Some breeds such as the Beagle have an apparent increased risk for developing hypothyroidism. Sex is not recognized as a predilection.
Beagles with hypothyroidism will usually show some sign of mental dullness, exercise intolerance or an unwillingness to exercise, lethargy, and have a tendency to gain weight without an increase in food intake or appetite. Often these signs are gradual in onset and subtle.
Some additional clinical signs typically involve the skin, neuromuscular system, or reproductive system. Changes in the skin and haircoat are common and include a dull, dry and easily epilated haircoat; symmetrical hair loss on the trunk and tail; scaly skin; puffiness of the skin; slow regrowth of hair; and bacterial infections. Neurologic signs include circling, seizures, head-tilt, drunken gait, and facial nerve paralysis. Reproductive signs in females include prolonged interestrus intervals, and in males, a low sperm count, a lack of libido, and atrophy of the testicles.
In juvenile Beagles hypothyroidism causes cretinism. Abnormalities in hypothyroid pups are usually related to the skeletal and central nervous system. Canines with cretinism will appear physically disproportionate, have large broad heads, wide square trunks and short limbs, and thick protruding tongues. These pups will be lethargic and mentally dull and will lack the typical playfulness seen in normal pups. Additional clinical signs include hair loss, inappetence, persistence of the puppy haircoat, goiter, and delayed eruption of the teeth.
Diagnosis of hypothyroidism will require a careful assessment of the history, clinical pathology, physical findings, and serum cholesterol and thyroid hormone concentrations, usually serum thyroxine (T4) concentration. In most dogs a normal level level of circulating thyroid hormone usually indicates normal thyroid function. A low serum thyroid hormone concentration along with increased blood cholesterol levels and appropriate clinical signs will support a diagnosis of hypothyroidism. A definitive diagnosis will then rely on response to trial therapy with the supplementation of thyroid hormone.
Treatment of hypothyroidism is done with the use of synthetic thyroid hormone, usually given orally twice daily. The dog must receive treatment for the remainder of his life. The clinical signs should resolve with appropriate treatment and the prognosis for recovery is excellent.