It sounds as though your cat may well be really constipated if she has not had a BM in 2 weeks. My guess is that there is a lot of very hard stool in there, and she is going to stop eating soon as you are right, there will be nowhere for it to go! The longer she goes without a BM, the harder it will be.
Whenever I have a previously normal cat that develops constipation, it makes me wonder about an underlying problem.
I have some suggestions to help your cat to have a bowel movement. These are:
1. Probably the fastest way to help her would be to use Pediatric rectal suppositories made for human infants.
They should be available at any pharmacy. They include dioctyl sodium sulfosuccinate (DSS, ColaceTM), glycerin or bisacodyl (DulcolaxTM). I usually suggest the glycerin suppository. It comes as a little cone about 1inch long. For a cat, you would GENTLY insert this into the rectum. It usually helps within an hour.
2. Offer her some milk - about 2 tablespoons every 2 to 4 hours. This has a natural laxative effect and may help to move things along.
3. Switch to all canned diet, if she'll eat it. The first ingredient is WATER which is going to help with any dehydration and thus the constipation. You could stay with your current brand but but use the canned (soft) type.
4. Add fibre by adding to her diet some PLAIN canned pumpkin, not pie filler (a couple of teaspoons twice daily), bran cereal (1 teaspoon twice daily), or Metamucil, Konsil, Siblin or similar product (1/2 teaspoon a day).
5. Try a hairball remedy like laxatone, tonic-lax or petromalt. All of these are essentially vaseline with flavouring added. Many cats love them! You could start at 1/2 teaspoon daily and see how she does.
6. Really encourage your girl to drink water.
Offer her water in a large, flat bowl since cats don't like to have their whiskers touch the edge when they drink (which is why lots of cats like the toilet bowl). If she likes dripping water, leave a tap dripping for her. Offer her the water from a can of tuna, diluted with tap water 50:50. Offer bottled water and see if she prefers it. Offer chicken broth, diluted 50:50. Try a few drops of clam juice in water. See if she likes water with an ice cube in it. See if she likes it out of a cup or martini glass.
7. Exercise can help relieve constipation.
Try getting her to chase a string around the house for a few minutes 2 or 3 times a day.
8. Polyethylene Glycol (Miralax or Glycolax are trade names) is another medication that your vet could prescribe. It is reported to have excellent results. Also, it's easy to use - just mix the powder (1/4 - 1/2 tsp twice daily) into the food. Start at the lower dose and adjust based on feces 1 to 2 days later (after giving it time to work).
Polyethlyene glycol is what all the veterinary gastrointestinal specialists seem to be recommending these days. So, you might want to talk with your vet about that.
9. Consider adding another litter box in another location. The idea with this is that if your girl needs to defecate, she has a litter box nearby and doesn't just decide to "hold it" until later.
I do, however, feel that you and your vet might need to do some blood tests if these have not been done already to determine if there is an underlying problem such as kidney disease that is leading to your kitty's lack of appetite and her constipation.
Clearly, there is something going on with your cat to cause her to have lost 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, 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 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:
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. Unfortunately, we also have to consider neoplasia (cancer) because your kitty is older and there has been 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 or possibly neoplasia. From what you have described, my best guess would be that CRI (kidney disease) 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 and to prevent further constipation! I encourage you to take her in soon as she is a senior citizen.
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.