Sorry for the long delay! I had a dental appointment (fun fun!) and was away from the computer for a number of hours.
Thanks for the additional information! AND the photo! What a cute cat, and looking very comfortable there in her nest of blankets. The photo is actually very helpful because I can see what size she is, AND that her coat is a bit "starey." You see above her back leg how the hair stands apart like that? And you can see her grey undercoat? In a young cat, it does not do that. That is not a symptom of one particular problem, but certainly adds support to my suspicions about what may be going on!!
I'll come back to that!
So, clearly, there is *something* going on with your cat to cause her to have lost so much weight recently. She is a senior citizen and a bit of a puzzle since she is giving us so few clues. The things that I would consider would be chronic renal insufficiency (CRI, kidney failure), hyperthyroidism (over active thyroid gland), or a combination of the two, diabetes and unfortunately we also have to consider neoplasia (cancer). These are the most common problems that I see in senior cats.
With chronic renal insufficiency cats tend to drink more, lose weight and have a diminished appetite. Some have vomiting. Many have dry hair coats and hair loss.
With hyperthyroidism, however, they tend to drink more, lose weight and have an INCREASED appetite. Some have vomiting, many have diarrhea.
With diabetes, cats also tend to eat and drink more, and have dry hair coats and hair loss as well.
With neoplasia, they may eat more or eat less, and lose weight.
As you can see, many of the symptoms overlap and with your kitty I don't know which of these descriptions fits best. All are treatable, to different degrees. Let me explain a bit more about each of them and the treatment options:
1. Chronic renal insufficiency. With this disorder, the kidneys have lost the ability to concentrate urine. So, the patient just produces dilute urine all the time, regardless of what is going on. For a cat with normal kidneys, if they don't drink for a while (say, because of feeling nauseated with a hairball), the kidneys just concentrate the urine and the cat keeps normally hydrated. Same as with a human who doesn't drink all night - the first morning urine is more concentrated because the kidneys are retaining all the water they can.
Now, if your cat's kidneys can't DO that, and just keep producing large quantities of dilute urine, she is going to start getting dehydrated. One of the first things that happens is that the body tries to draw water out of the feces and the cat gets constipated because the feces are now dry and hard, so it's harder to pass them. Also, as the patient becomes slightly dehydrated, she tends to lose her appetite. Imagine yourself being really thirsty and someone offering you a steak. No matter how delicious you might think that is, you would be unable to eat much without having a drink first.
Kidney disease can be diagnosed by physical exam and analysis of a blood and urine sample. On a physical exam, I check the kidney size and shape. For treatment, the first step is a low-protein diet available through your vet clinic. The patient may also need supplemental potassium, and perhaps fluids given under the skin to correct any dehydration.
Here is more information:
2. Hyperthyroidism. This is a common disorder of older cats in which the thyroid gland in the neck starts to over-produce a hormone called T4. T4 controls metabolic rate. So, the more you have of it, the faster the metabolism. Cats that are hyperthyroid tend to eat voraciously, but lose weight because they burn the calories up so fast. Their heart rates increase, and the transit time through the intestines increases. So, they may develop diarrhea and vomiting, but not always.
Hyperthyroidism can be diagnosed by physical exam and blood and urine analysis. On a physical exam, I check for enlarged thyroid glands, and a rapid heart rate, and sometimes heart murmurs. Blood and urine tests allow a vet to confirm the diagnosis.
Hyperthyroidism responds really well to treatment.
The treatment options are oral medication (usually twice daily, always for the rest of kitty's life), surgery, or radioactive iodine treatment (this last is the BEST treatment because it gives you a cure, but it is expensive).
3. Diabetes mellitus is also on the list of possibilities. When a normal animal eats, the intestines absorb the calories into the bloodstream as glucose. So, now there is a lot of glucose in the blood. BUT it cannot get into the muscles or other cells that need it without insulin. You absolutely have to have insulin to get glucose from the blood into the cells. And it is the cells that need the glucose; the bloodstream is just a road that delivers it to the cells.
So, now there is a lot of glucose in the blood and it can't go anywhere. This then starts to spill into the urine - so now you have glucose in the urine. Glucose is a really large molecule, and where-ever it goes, it pulls water with it. So, all that glucose in the urine pulls a lot of water out into the urine with it, and suddenly the animal is urinating large quantities. This makes her dehydrated, so she has to drink huge amounts to try to stay hydrated.
Animals with diabetes thus drink an enormous amount of water. Also, they have ravenous appetites because their cells are starving as none of the glucose can get into them. So, they eat a lot and urinate a lot.
Diabetes can usually be managed with insulin injections and/or with prescription food plus pills depending on how far advanced it is.
I'll give you some links to further information:
4. Unfortunately, we also have to consider neoplasia (cancer) because your kitty is older and there has been dramatic weight loss. Hyperthyroidism and CRI are FAR more common, however, so don't panic! To diagnose cancer, a vet would start with a complete physical exam to try to feel for internal masses, and would do blood work to rule out other problems. X-rays and biopsies might be needed.
If the tests for hyperthyroid disease and CRI were negative, and other blood tests were all normal, I would have to start considering cancer, unfortunately.
Some forms of cancer grow as a mass or lump and can be palpated in the belly or seen on x-rays. Some forms of cancer invade as tiny little cells all through-out an organ like the gastrointestinal tract. They are hard to detect because you can't palpate them, and you can't see them on an x-ray because they are scattered throughout the organ. In these cases, ultrasound and biopsy or exploratory surgery and biopsy can be used to make a diagnosis. Looking at a piece of the organ under a microscope is the only way to see if there are cancer cells there. Many types of cancer in cats respond really well to chemotherapy medication. There are even chemo protocols that consist of pills that the owner can give at home. Cats have minimal side effects from many chemo drugs - NOTHING like as severe as humans.
There are so many forms of cancer that it is hard for me to provide a link, but I'll give you one for a common type of cancer:
So, in summary, it sounds as though your cat may have hyperthyroidism, CRI, diabetes or possibly neoplasia. From what you have described, my best guess would be that CRI (chronic renal insufficiency) is most likely. A check up and blood tests with your vet will help to make this diagnosis, and get her started on treatment to help her gain weight! I encourage you to take her in this week as her condition sounds serious!
Also, I strongly suspect that the howling and abnormal behaviour you are seeing after she eats may be due to something called uremic gastritis, which we can see with kidney disease. This is like heartburn, and is fairly common with cats with CRF.
With uremic gastritis, there is too much stomach acid produced and cats can reflux into their esophagus. As with heartburn in humans this is very irritating, and may be why she howls and appears so uncomfortable after eating.
This is something that can be treated with antacids like cimetidine, famotidine or ranitidine (also known as Tagamet, Pepcid and Zantac resptectively). I will give you links:
Legally I cannot prescribe drugs for a cat I have not examined. I can tell you, however, that I often suggest people purchase Pepcid AC for cats with uremic gastritis and give 1/4 of a 10mg tablet twice daily. I would recommend you talk to your vet about whether this may be appropriate for your kitty.
More about esophagitis (inflammation of the esophagus from reflux of gastric acids): http://www.petplace.com/cats/esophagitis-in-cats/page1.aspx
And more about CRF and uremic gastritis:
So, although I can't tell you what is wrong with your kitty, I hope I have given you some directions to explore with your vet. :-)
If this has been helpful, please Accept my answer and leave feedback. I will still be here to provide further information if you need it!
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.