Can a cat be too skinny? Yes! A healthy cat should have a small amount of fat padding over the ribs. When you press in just a little and move that skin back and forth over the ribs (the way you'd move a shirt over the ridges of a washboard), you should be able to feel those ribs. A cat who's too skinny -- and especially a cat who loses weight quickly -- needs to see the veterinarian.

When an older cat becomes skinny, it may be a relatively common malady called hyperthyroidism. In cats with this disease, the thyroid gland starts overproducing its special hormone, making these cats lose weight and often seem more active than normal for older cats. Veterinarians sometimes call the condition "zoom around the room" syndrome. Left untreated, hyperthyroidism can be deadly. Fortunately, treating the disease is a real veterinary success story.

The overactive thyroid can be persuaded to slow down using drugs, surgery or radiation therapy. Radiation therapy involves a hospital stay, but it usually resolves the problem permanently. Other pet lovers decide on surgery or daily medication. If you're facing this decision, discuss all the options with your veterinarian, and choose what's right for you and your cat.

Hyperthyroidism is what makes many cats look like a rack of bones, but it's certainly not the only possible problem. The cat could have a digestive problem, suffer from a severe internal parasite infestation, or even have an autoimmune disease. If you're free-feeding in a multicat household, your skinny cat may simply be losing out at the trough.

Bottom line: A cat who's too fat or too skinny needs to be checked out by a veterinarian.