The tail of a cat is incredibly expressive; it lets other cats (and observant humans) know when she is feeling curious, content, irritated, or threatened. It is also critical for balance. Made up of many hinged vertebrae segments, the tail is surrounded by muscle and tendons that allow it a great deal of movement. Problems with the tail can range from a simple hygiene-related condition to serious nerve damage caused by an injury.
Stud tail is a condition that typically affects unneutered male cats (hence, the name); however, it can affect any cat, including females, and neutering a male will not necessarily get rid of the problem. A cat with stud tail has overactive sebaceous (skin) glands at the base of his tail. They begin to secrete too much of the greasy substance that normally helps to lubricate the skin. As a result, the fur around the base of the tail starts to look greasy and unkempt, and the may even fall out. There might be a waxy substance on the tail, and occasionally a bad odour as well. Sometimes this condition is the result of an infection that will require antibiotics, but usually, washing the tail with a medicated shampoo that your veterinarian can provide will take care of the problem.
A cat with hyperesthesia will have muscle spasms down the back and tail that can seem to drive him crazy. The affected cat will often run around wildly and chase, bite at, or lick his tail and back. (It has also been called "twitchy cat disease.") (See References 1) Because the cat with hyperesthesia exhibits very sensitive nerves and skin, even a light touch can set off the muscle spasms. Some veterinarians believe that hyperesthesia is an anxious, or nervous condition, and may wish to try treating it with antidepressants or anti-anxiety medication. (See References 1) In case the condition is being set off by dry or allergic skin conditions, you may be asked to try using a medicated shampoo to bathe your cat.
Broken tails are nearly always the result of an unfortunate accident. According to Feline Express, common causes of tail breakage include getting it caught in a closing door, someone stepping on the tail, pulling the tail to catch the cat as it is running by, car accidents, and fights with other cats (where severe bites can cause a break). (See References 2) Swelling in the tail, or any strange lump can indicate a break. Other signs to look for include a cat that is dragging its tail or having difficulty walking, and a tail that is painful or, conversely, seems to have no feeling at all. Any of these symptoms, especially if accompanied by loss of bowel or urinary control can indicate nerve damage. Most breaks will heal, but severe nerve damage may necessitate the amputation of the tail.