Hypothyroidism in Dogs is Incurable but Treatable

One of my dogs has always been a bit sluggish and overweight. But she's been tested for hypothyroidism a couple of times with negative results. You can't blame a veterinarian for thinking that she's hypothyroid, though, because many dogs have an underactive thyroid. In fact, hypothyroidism is the most common endocrine disorder in dogs middle-aged or older. Labrador and Golden Retrievers, Shetland Sheepdogs, Great Danes, Irish Setters, Doberman Pinschers, Dachshund, Miniature Schnauzer, Cocker Spaniel, Airedale Terrier and Old English Sheepdogs are particularly prone to hypothyroidism. Miniature and toy dogs rarely contract this disorder. Interestingly, spayed females are more predisposed to it than unspayed females. However, intact females with hypothyroidism can have serious reproductive problems and intact males may be infertile or lack libido.

What is hypothyroidism? It's a disorder characterized by a decreased metabolic rate because of impaired secretion and production of thyroid hormones. According to the Merck Veterinary Manual, hypothyroidism is one of the most over-diagnosed diseases in dogs. One confusing factor is that even in dogs with normal thyroids, clinical signs of hypothyroidism may improve with administration of thyroid hormone. As well, temporarily low serum thyroid hormone from a non-thyroid illness or certain drugs can occur. And many of the signs of hypothyroidism can mimic other diseases. So the successful diagnosis of true hypothyroidism depends on clinical signs, lab testing, and demonstrating low serum concentrations of free thyroid hormones that do not respond to TSH (thyroid stimulating hormone) administration.

What are the signs of hypothyroidism? Besides lethargy and obesity accompanied by a lack of appetite, symptoms of an underactive thyroid include a scanty, coarse coat that sheds easily. The skin toughens and darkens. The dog may suffer from chronic skin infections or seborrhea (oily skin secretions). These changes usually affect the neck and body. Hypothyroidism can also cause eyelid drooping, facial puffiness (myxedema) and neurological disorders, behavioral changes and mental sluggishness, and heart or gastrointestinal problems. The dog may seek heat because its temperature-regulating mechanism is not functioning properly. Another sign of hypothyroidism is a condition called idiopathic follicular atrophy, in which the follicles of the thyroid are replaced by fatty or connective tissue. If left untreated, hypothyroidism can lead to serious complications, including coma, dangerously low blood pressure, suppression of breathing, and bradycardia (slow heart rate).

There are two basic types of hypothyroidism: Most dogs (about 95 percent) belong to the category of primary hypothyroidism, which results from destruction to the thyroid gland through inflammation or atrophy. Secondary hypothyroidism, the less common type, results from damage to the pituitary gland by a tumor. The pituitary gland secretes the hormone thyrotropin, which helps the thyroid gland to function properly. There are also rarer forms of hypothyroidism that involve cancer and congenital factors. Some signs of the less common types of hypothyroidism are dwarfism (underdevelopment of body), cretinism (arrested mental and physical development) and goiter (visible enlargement of the thyroid).

What's the treatment for hypothyroidism? The traditional treatment is straightforward: synthetic thyroxine (T4) supplements for life. An alternative natural treatment is glandular thyroid supplements taken either with or without conventional medication.

Hypothyroidism is a very treatable but incurable lifelong condition. Once on the medication, the dog should be tested twice a year to make sure the dosage is appropriate and that he is absorbing the medication adequately.