Underactive thyroid, also known as hypothyroidism, is a thyroid gland disorder in which the thyroid puts out too few iodine-based hormones, usually due to a disease called autoimmune thyroiditis. It can be caused by genetic factors, environmental pollutants, atrophy of the thyroid gland or chemical poisoning. Some symptoms of hypothyroidism in dogs are similar to those of humans afflicted with the same disorder.
Breeds That Are Susceptible
Hypothyroidism doesn't treat all dogs the same way. Depending on the dog's size and breed, the disease can be predominant or almost nonexistent. Typically, large and midsize breeds are prone to the condition, and certain breeds are most susceptible: German shepherds, boxers, greyhounds, beagles, dachshunds, cocker spaniels, Airedale terriers, Great Danes and Doberman pinschers. The miniature breeds, with the exception of the miniature schnauzer, are least affected by underactive thyroid.
Itchiness, Skin Disorders and Hair Loss
Hypothyroidism causes dry skin and itchiness, causing an affected dog to scratch relentlessly and create tears in the skin. These lesions heal slowly, because the animal keeps ripping them open again. Bald spots form due to the condition called alopecia. The fur loosens and falls out in clumps, failing to grow back, making the dog look like he has mange.
Onset at Puberty
Male dogs with underactive thyroids at the time of puberty develop atrophied testicles and lowered sperm levels, causing low fertility and poor breeding capacity. Female dogs with the same condition typically have fewer menstrual cycles than normal, and abnormal pregnancies; when they do achieve successful pregnancy, they tend to give birth to weakened puppies. Pups born to a mother with hypothyroidism have a high death rate due to this immune system weakness.
Face and Head Disorders
Dogs with hypothyroidism often have sad facial expressions, complete with drooping eyelids. Some dogs with underactive thyroid also have facial paralysis and tilt their heads a lot as a result of inner ear disruption and dizziness. It's common for these dogs to have chronic ear infections, sometimes serious enough to result in deafness. They suffer from eye infections that cause blindness; they often lose their sense of smell and taste.
Anemia, Depression and Fatigue
Dogs with decreased thyroid production sleep a lot, and are always tired and listless. They are prone to mood swings, can be suddenly aggressive toward people and other animals, and can suffer weakness of muscles, leading to fatigue and lethargy. These dogs are often anemic, which is a cause of weakness and lethargy. These animals have very little tolerance for activity, can't handle the cold, have low energy levels and have slow heart rates.
In congenital hypothyroidism, the dog inherits the disease from the parents and is born with it. This condition shortens the legs, causing dwarfism, and broadens the skull, making the span between the ears appear flat. It causes goiter, swelling of the thyroid gland in the neck. Congenital hypothyroidism also causes teeth to grow unusually slowly, a condition called macroglossia. Polyneuropathy, a condition whereby the peripheral nerves deteriorate, is common with this disease.
Besides lethargy, hypothyroidism causes brittle toenails that get infected easily, painful joints similar to arthritis pain, and incontinence that causes dogs to urinate uncontrollably. Stomach and gastric issues are common, including nausea, constipation and diarrhea. Dogs with hypothyroidism may have unpleasant-smelling skin. Dogs with hypothyroidism can get disoriented within their longtime surroundings. Some dogs may develop epileptic seizures, or may breathe very fast. Limb swelling, pain and lameness are common.