• Even young cats can develop hyperthyroidism.cat 4 image by Dragan Saponjic from Fotolia.com
  
  Feline hyperthyroidism is typically caused by a benign tumor that increases the amount of thyroxine in the cat's bloodstream. While this disease can be diagnosed in young cats, it is most common in older cats, and the symptoms can be subtle enough that it can be attributed to aging. Recognizing the signs of hyperthyroidism in cats can help diagnose this issue and control it.
  
  

Weight Loss

• According to Pet Education, about 90 percent of cats that are affected by hyperthyroidism will evidence weight loss. This often results from the anorexia and appetite loss that comes with hyperthyroidism, but the weight loss can also be seen in animals that seem to be eating healthily.
  
  

Vomiting

• Cats that are dealing with hyperthyroidism often suffer from digestive upset. They may be trying to purge something uncomfortable in their systems, or they may simply be unable to keep food down. Vomiting can contribute to weight loss, and it can also result in dehydration. You should take a cat that is vomiting to the veterinarian.
  
  

Excessive Drinking

• Hyperthyroidism can also manifest itself in excessive thirst, which results in a cat constantly draining its water dish. The cat will also have an increased urge to urinate, and this can become severe enough that a cat that is thoroughly house-trained will end up urinating on the floor.
  
  

Poor Coat

• Because hyperthyroidism has such a severe effect on the cat's digestion, a poor coat can result from the fact that the cat is unable to retain nutrients. The cat's coat might be coarse or brittle. A cat whose coat quality changes suddenly should be examined by a veterinarian.
  
  

High Heart Rate

• A cat that is affected by hyperthyroidism may have a high heart rate. Even when the cat is lying still and has not exerted itself, its heart might seem to be beating very quickly.
  
  

Labored Breathing

• A cat that is dealing with hyperthyroidism may seem to have issues breathing, even when it is lying perfectly still. It might simply breathe noisily or it might seem to have issues drawing breath at all.