What is Feline Hyperthyroidism?
Hyperthyroidism is a wasting disease caused by increased thyroid hormones, resulting from one or more benign tumors (adenomas) of the thyroid gland. With time, the adenomas may evolve into more aggressive, and rarely, malignant tissue ( adenocarcinoma.)
High thyroid hormones cause an increased metabolism, leading to weight loss. Cats, carnivores, burn protein more readily than fat for energy, seen as muscle wasting over the spine, hips and back legs, sometimes despite a chubby tummy. Some cats have more difficulty jumping up onto furniture due to muscle weakness. Most cats try to compensate by eating more ( polyphagia.) Some cats are so ravenous, they steal food off the kitchen counters or the owners’ plates! Other cats may become pickier, even though they may act hungrier. While the weight loss may happen quickly, it may also be so gradual that some owners may not even realize it has occurred. Many hyperthyroid cats have increased urination, and need to drink more water to catch up to their fluid losses. Hyperthyroidism usually leads to behavior changes, which may include agitation, anxiety, and even aggression toward animals (including human companions.) Owners frequently describe their cats “jetting up and down the halls”, or as “more playful” or “ clingy.” The agitation makes some cats “talk more.” These become more vocal, and may restlessly ‘haunt the house’ caterwauling. Some hyperventilate (pant), especially if stressed, e.g., in the car or veterinary office. Most have high heart rates, even when in a relaxed environment. Vomiting and diarrhea may be caused, or at least worsened, by thyroid disease, even if caused by a different (non-thyroidal) problem, such as inflammatory bowel disease. Some cats groom excessively when they’re anxious from hormonal duress, licking or snatching tufts of fur out, leaving bald or ‘moth-eaten’ areas. Some groom less, allowing flake and oil to build up in their coats, making them look ‘scruffy.’
Over time, untreated or poorly controlled hyperthyroidism leads to deleterious effects on many of the cat's internal organs. Heart failure, kidney and liver disease, muscle wasting, chronic emaciation, and/or severe metabolic dysfunction can develop, ultimately leading to death.