What is Apathetic Hyperthyroidism?

What is Apathetic Hyperthyroidism?
By Janet Tobiassen Crosby, DVM, About.com

Question: What is Apathetic Hyperthyroidism?

Hyperthyroidism is an endocrine disease that is very common in senior cats. This disease is caused by an overproduction of circulating thyroid hormone by the thyroid gland. There are many possible clinical signs; animals will present a few or many of the signs. The most common signs seen in cases of hyperthyroidism are often absent in what is known as Apathetic Hyperthyroidism.

Answer: I received the blood results back today (9/25/07) for my soon-to-be sixteen year old cat, Herman Roosevelt Quinn. The results were as I suspected: hyperthyroidism. The results were as I suspected because he has lost some weight in the last 2-3 weeks and I can feel a small nodule in his neck. His heart rate is elevated as well (180-220 bpm). That was it for signs that are commonly seen with hyperthyroidism; a common endocrine disorder of elderly cats.

The typical signs for hyperthyroidism are many and varied.
Rarely does a cat show all of the signs, but the most common clinical signs are:

  Weight loss, often despite an increase in appetite
  increased appetite, demanding food more often
  Vomiting and diarrhea
  Increased energy or irritability
  Drinking and urinating more
  Increased heart rate (difficult to assess for owners)

I adopted Herman when he was about 7 months old. He had been abandoned, and always acted like every meal was his last (i.e. a great appetite!). Herman's main clinical signs were lethargy and weakness. He seemed to age before my eyes. Once a robust "talky" kind of cat loaded with personality, he seemed to always be sleeping and just not have that "spark". These changes were subtle at first, and I had to keep reminding myself that he is getting up there in age (as much as I hate to admit it), but something just wasn't adding up.

Apathetic hyperthyroidism is described as a case in where the patient is lethargic, weak and in some cases, anorexic. These symptoms are rare, and are directly opposite from what is seen in "classic" hyperthyroid cases.

Thankfully, Herman's case has been caught early; his thyroid values are not sky high and the rest of his bloodwork looks OK for his age. Treatment will be started shortly.