We don't see a whole lot of different liver diseases in cats. And for what we do see, the treatment for all of them is pretty similar. The most common liver disease that we see in cats is hepatic lipidosis, also known as fatty liver disease. After that, we see suppurative cholangiohepatitis, non-suppurative cholangiohepatitis, and cancer. Now, there are other liver diseases, but they are pretty rare, and the only way to diagnose them is with a liver biopsy, which requires an abdominal exploratory surgery. The good news is that first three listed tend to respond nicely to treatment.
Hepatic lipidosis happens when your cat is used to a certain caloric intake, and for what ever reason, a diet change, stress in the environment, or other systemic illness, your cat's appetite drops off sharply. The body is used to a certain level of energy for its processes, so it starts digesting the fat stores in the body. The more overweight your cat is, the faster this process happens. As the body is going through the fat stores, the fat starts backing up into the liver. The liver eventually becomes so full of fat, that it is almost non-functional. We can often even see this on ultrasound - the liver is very bright and reflective because it is so full of fat.
The good news is that with aggressive treatment, 99% of cats will survive this. The first thing we do is to place an esophageal feeding tube in your cat. One of the mainstays of treatment is high calorie intake. Your cat is nauseous from the liver disease, and will not, no matter how much you coax or try to hand feed them, get enough calories in. A feeding tube makes it much simpler to get food into them, it is just a little more time consuming on your part, because you will be the one feeding them. Plus, you can also crush most of the medications and give them through the feeding tube, mixed in the food. We also treat with liver medications, anti-nausea medications, and because there is often a secondary infection, antibiotics. Treatment can last anywhere from 3 weeks to 3 months depending on how advanced the hepatic lipidosis is, and how often you are able to tube feed your cat. If your cat does not start improving after a month though, then we start looking for other liver diseases.
Suppurative cholangiohepatitis is when your cat gets a bacterial infection in their liver. These tend to be anaerobic infections, and can sometimes simmer for years before they cause clinical signs. If we suspect suppurative cholangiohepatitis, we may put your cat on antibiotics for 2-6 months to completely eradicate the infection. We will also treat with liver medications, anti-nausea medications, appetite stimulants, and possibly place a feeding tube short term. The symptoms of this disease are very similar to hepatic lipidosis other than your cat may still be eating, although much less than normal. We may also be able to see debris in the gall bladder on an ultrasound, which could indicate infection. A biopsy is ideal, but since that requires major surgery, most owners elect to just try the meds.
Non-suppurative cholangiohepatitis is a auto-immune disorder where your immune system will actually attack your liver. This may be triggered by suppurative cholangiohepatitis, but often we won't know the cause. If we are treating for liver disease, and your cat is getting worse rather than better, we may try adding an immunosuppressant such as a steroid. If it makes a significant difference, that may lead us towards non-suppurative as a diagnosis. Of course the ideal is to do a biopsy of the liver to know for sure, but not every owner can afford that, or wishes to put their cat through the procedure, so most cats are treated presumptively.
Cancer. The most common type of cancer in the liver is lymphoma, but the liver can develop other kinds of cancers as well. If the cancer is a primary liver cancer, and is caught early before it spreads, removal of that liver lobe may be curative. Sadly however, we don't usually find liver cancer until it has spread past the point of a surgical cure.