Skin problems in dogs with hypothyroidism are not an unusual ordeal considering the way hormones affect the dog's body and the skin. In order to better understand the impact of this condition on the dog's skin, it helps to gain a better understanding on how the thyroid gland works and the effect of the thyroid glands on the dog's body. Dr. Ivana Vukasinovic provides details about the impact of low thyroid levels in dogs and the common skin problems in dogs with hypothyroidism.
Hypothyroidism in Dogs
The thyroid gland, one of the essential glands in the body, produces thyroxine (T4), a hormone that controls metabolism, along with other thyroid hormones. Hypothyroidism is a deficient activity of the thyroid gland. As a result of this deficiency, lower production and excretion of T4 and T3 occur, and lower quantities of these hormones will cause a slower metabolism of the dog.
Hypothyroidism is usually more common in older dogs, and it is also more commonly diagnosed in medium or giant breeds, with some breeds being more genetically predisposed. Commonly affected breeds include Doberman pinschers, Irish setters, golden retrievers, great Danes, old English sheepdogs, dachshunds, miniature schnauzers, boxers, poodles, and cocker spaniels.
The cause behind this condition is usually unclear; most likely reasons are tumors, shrinking of the thyroid and pathological reaction of the immune system that attacks the thyroid (autoimmune or immune-mediated). Other reasons can include congenital disease, post-surgery effects, after-effects of medications, iodine deficiency.
Regardless of the underlying cause, the symptoms and treatment for hypothyroidism are usually always the same.
Symptoms of hypothyroidism include changes in mental status, lethargy, weakness and inactivity, dullness, intolerance to cold, weight gain and obesity, and various different skin problems.
Skin Problems in Dogs With Hypothyroidism
Myxedema is a medical term that refers to changes in the skin caused by hypothyroidism. Homeostasis of the epidermis is regulated by the thyroid gland, and in cases of hypothyroidism, increased deposits of glycosaminoglycans are present in the skin.
This is caused primarily by the accumulation of hyaluronic acid and chondroitin sulfate in the skin, which leads to calcification areas, where the skin appears almost scaly and very dry. These mucopolysaccharides and increased dermal water content alter the refraction of the light giving the pale color of the skin.
These are the most frequent problems of thyroid dysfunction, but usually, all skin changes can be divided into three categories with distinctive changes:
- Autoimmune skin disease associated with thyroid dysfunction (Myxedema, urticaria, pruritus, vitiligo, bullous disorders, eczema, Connective tissue diseases)
- The direct effect of hormones on skin tissues (scaly skin, myxedema, dry and coarse hair, alopecia, dry skin, decreased sweating)
- Skin manifestations of hormone action on non-skin tissues (cold intolerance, purpura, pallor, dropping of eyelids)
Thyroid hormone is irreplaceable for the biology of the epidermis, dermis, and hair. Receptors for the thyroid hormone are present throughout the skin, including hair follicles. For example, T3 hormone enhances epidermal differentiation and growth, and has an irreplaceable effect on the glands, and synthesis of glycosaminoglycans.
Thyroxine (T4), on the other hand, stimulates the proliferation of hair follicle keratinocytes and T3 inhibits their apoptosis. As said, hypothyroidism may be a result of target cell resistance to hormones or inadequate hormone production and circulating levels.
Types of Skin Problems in Dogs With Hypothyroidism
The first symptom of skin problems in dogs with hypothyroidism is cold and pale skin. Thyroid hormones, or lack of them, affects thermogenesis (the production of heat) and as a result, we have diminished core temperature and reflex vasoconstriction as a compensatory mechanism.
The dryness of the skin is a result from reduced function of the eccrine glands, affected by the lack of T3. Xerosis, the medical term for dry skin, is the most common manifestation of the skin changes in hypothyroidism. Xerosis is the change in skin texture leading to rough, dry skin covered with scales as a result of poor hydration.
As already said, the first symptoms include pale and cold skin, flaky with scales, and with a dull and thin coat, but, almost never red or itchy (like in cases of flea infestation). Itchy skin can be caused by a possible skin infection.
Black patches of skin in the areas of friction accompanied by thickening of the dog's skin, increased hair shedding with hair loss on the back legs, trunk and tail are the most frequent changes in the skin due to hypothyroidism. Ear infections, as well as toenail infections, are common.
"In moderate to severe cases, thickening of the skin occurs secondary to accumulation of glycosaminoglycans (mostly hyaluronic acid) in the dermis. In such cases, myxedema is most common on the forehead and face, resulting in a puffy appearance and thickened skin folds above the eyes. This puffiness, together with slight drooping of the upper eyelid, gives some dogs a “tragic” facial expression." ~Merck Veterinary Manual
At the Vet's Office
Many different diseases can mimic hypothyroidism making this condition one of the most over-diagnosed diseases in dogs. Clinical signs with several blood tests will be necessary for the proper diagnosis of this condition. After the diagnosis, regular monitoring of dog’s thyroid levels is necessary (one or twice a year).
Hypothyroidism in dogs is treatable, but it requires a lifelong therapy. The treatment is an oral replacement hormone, and the dosage will depend on the dog’s weight and present thyroid levels. Usually, the dosage is adjusted over time, and first results are visible after a few months.
Two forms of thyroid medication are T3 and T4. Most dogs receive T4 (levothyroxine or L-thyroxine), which is converted to T3 by the body. Few exceptions cannot make this conversion and require T3 medication.
At first, therapy is given twice daily. In regards to skin problems in dogs with hypothyroidism, once the hair coat regrows and overall condition of skin begins to improve, which takes from 4 to 6 weeks, dogs can be medicated once daily. As ear and nail infections are associated with this disease, ears, and nails should be cleaned and treated as well if necessary.