Hypothyroidism: Thyroid Disease in Dogs
Laurie Anne Walden, DVM
The thyroid, a gland in the throat, produces hormones that regulate many body functions. In dogs, the most common thyroid disorder is hypothyroidism, or low thyroid hormone production. Naturally occurring hypothyroidism is rare in cats.
In dogs, hypothyroidism almost always happens either for no known reason or because of an immune system condition called lymphocytic thyroiditis. Rare causes are cancer and thyroid malformation that’s present at birth. Hypothyroidism is more common in medium and large breeds than in toy breeds. Some breeds may be more likely than others to develop hypothyroidism :
Decreased thyroid hormone levels reduce the overall rate of metabolism in the body and affect many body systems. Changes in the coat and skin are the most common results of hypothyroidism, but some dogs have few or no symptoms. The signs vary from dog to dog and can include the following:
The signs of hypothyroidism are not specific; they can be caused many disorders other than hypothyroidism. Some symptoms can improve with thyroid hormone supplementation even if the dog doesn’t have hypothyroidism. For this reason, hypothyroidism can’t be diagnosed only by the signs or by response to treatment.
Diagnosing hypothyroidism in dogs generally requires blood tests for more than 1 type of thyroid hormone. One of the main hormones produced by the thyroid is thyroxine (T4). Animals with hypothyroidism have a low blood level of T4. Most of the T4 in the blood is bound to proteins. The blood level of protein-bound T4 can be affected by illnesses other than thyroid disease. A blood test for total T4 (which includes protein-bound T4) is sometimes used to screen for thyroid disease, but this test by itself isn’t reliable for diagnosing hypothyroidism. The blood level of free T4 (T4 that is not bound to proteins) is more accurate for diagnosing hypothyroidism. Your veterinarian might recommend additional thyroid function tests if thyroid disease is suspected but not clearly shown on the initial blood tests.
Hypothyroidism is treated by giving a thyroid hormone supplement. This medication is given by mouth once or twice daily for the rest of the dog’s life. Your veterinarian will likely recommend regular blood tests to be sure your dog’s dose is correct (for example, dogs that lose weight after a few months of treatment might need a different dose tailored to the new weight). Most dogs respond well to treatment.
Photo by Jamie Street on Unsplash
Laurie Anne Walden, DVM
Chocolate is one of the top 10 animal toxins reported to the ASPCA Animal Poison Control Center each year. As you shop for Halloween candy and get ready for the holiday season, remember to keep the candy bowl and baking supplies out of reach of your dogs. (Chocolate is dangerous for cats too, but they’re less likely than dogs to eat it.)
What’s Toxic About Chocolate?
The main toxic components of chocolate are methylxanthine compounds, specifically theobromine and caffeine. Cocoa beans and their hulls have relatively high methylxanthine levels. Cocoa butter (the fat from the cocoa bean) contains very little methylxanthine.
Humans process methylxanthines in the body at a different rate than dogs do, so foods containing chocolate and caffeine that are safe for people can be very risky for dogs.
As far as toxicity goes, not all chocolate is created equal: some types of chocolate are more dangerous to dogs than others. Products with high concentrations of cocoa liquor, which is made from cocoa beans, are the most toxic for dogs.
In general, the darker the chocolate, the more dangerous it is for dogs. Dry cocoa powder is more toxic than dark sweet chocolate, and dark sweet chocolate is more toxic than milk chocolate. Mulch made from cocoa bean hulls contains theobromine and is unsafe for dogs. White chocolate has very low methylxanthine levels and doesn’t cause chocolate poisoning.
Chocolate-containing foods can be dangerous for dogs for other reasons too. Dogs that eat food with a high fat content—this includes white chocolate—can develop pancreatitis, a disorder of the pancreas. Baked goods and candies may contain raisins, macadamia nuts, xylitol (a type of sweetener), or other ingredients that are hazardous to dogs.
How Much Chocolate Is Dangerous?
The severity of chocolate poisoning depends on 3 factors:
These 3 factors determine the dose of methylxanthine that a dog has received. The higher the dose, the more severe the consequences.
Figuring out the amount of methylxanthine in a chocolate product isn’t always simple because cocoa content varies. You can get a general idea of your pet’s risk by using a chocolate toxicity calculator like the one at veterinaryclinic.com. The ASPCA Animal Poison Control Center has a mobile app that includes a easy-to-use chocolate calculator and information on other potential hazards.
Signs of Chocolate Poisoning
The signs of chocolate poisoning depend on the dose of methylxanthine. Dogs that eat chocolate can also develop pancreatitis (from the fat content) or have toxic effects from other ingredients. Signs of methylxanthine poisoning usually appear within 6 to 12 hours and include the following:
What to Do if Your Dog Eats Chocolate
If your dog eats chocolate or a caffeine-containing product, estimate how much she ate and make a note of the ingredients. Save the product label if possible. Call your veterinarian’s office if you’re not sure if the amount was safe. If your dog has symptoms of chocolate poisoning or if the amount or type of chocolate was dangerous (for example, if your Chihuahua ate a 2-oz bar of dark chocolate), seek veterinary care right away.
Dogs with chocolate poisoning may need to be hospitalized for treatment. Your veterinarian might induce vomiting or might recommend that you do this at home—but don’t try to make your dog vomit without checking with your veterinarian first (induced vomiting is not always the best or safest approach). The prognosis depends on the severity of the symptoms.
Image credit: CDC/Debora Cartegena
Laurie Anne Walden, DVM
The contents of this blog are for information only and should not substitute for advice from a veterinarian who has examined the animal. All blog content is copyrighted by Mallard Creek Animal Hospital and may not be copied, reproduced, transmitted, or distributed without permission.