What is hyperthyroidism besides being a fifty-cent word?  Well in non-medical terms, it is an overactive thyroid gland.  For cat owners the most important things to know about the disease are its symptoms and that it is treatable.  The disease usually affects cats that are older, the average age being 14 years.

Weight loss is the most common sign.  Often up to 50% of body weight can be lost in a relatively short time.  Weight loss is not normal in older cats.  Cats that have the disease may become ravenous eaters when previously they were very picky.  Other outward signs of possible hyperthyroidism include an unkempt, greasy, easily matted hair coat.  There may be excessive shedding or hair loss in clumps.  The hair coat may change color, sometimes to red or brown.  Cats that were previously easy to groom may develop heavily matted coats.

Vomiting may occur since hairballs arise from the shedding or excessive grooming.  Stools may change to a gray color and become voluminous.  Water intake may increase and correspondingly there may be increased urination.

Often, hyperthyroidism is evidenced by restlessness and over activity.  Remember, it is unusual for an older cat to be awake for more than a few hours a day.  Sometimes the hyperthyroid cat becomes aggressive or difficult to control.  It may stop using the litter box or frequent unusual locations.  It may suddenly prefer cool bare floors or shady areas compared to its usual sunny warm spots.  This is because of increased peripheral circulation.  You may also notice that the cat may vocalize loudly when it is alone in a room.  This can be very eerie when done in the middle of the night!  I know, since I experienced this with my own older cat that I subsequently diagnosed with hyperthyroidism.

Finally, having described lots of symptoms evidencing over activity, there are some cats with the disease that have just the opposite symptoms.  They will have a poor appetite, be lethargic and very weak.

If you recognize any of these symptoms, you should bring your cat to your veterinarian for an exam and testing.  The physical exam may reveal that the thyroid glands are enlarged.  Lab testing can also be done, as can a thyroid scan.  If the diagnosis is hyperthyroidism, treatment can be by medicine, radioiodine treatment or surgery.  The preferred treatment is radioiodine.  This involves about a one-week stay at the specialist where the thyroid is shrunk through radiation.  Since treatment by medication is for life, it can often be much more economical in the long run to elect the radiation treatment.