Cat Losing Weight in Hindquarters: Symptoms, Diseases, and Age

A cat losing weight in the hindquarters is mainly losing muscle. In older cats, possible causes to investigate include sarcopenia, arthritis, kidney disease, hyperthyroidism, diabetes, and chronic digestive diseases. In young cats, consider intestinal worms first. To narrow down the cause, look at your cat’s age, appetite, thirst, and how quickly the change is happening. Rapid weight loss, a cat that has stopped eating, or a kitten losing weight calls for a veterinary visit without delay.

Key takeaways

• The typical sign: the hips and pelvic bones become visible, and the thighs grow thinner, while the rest of the body still looks normal.
• When to take action: a loss of 5% of body weight warrants a checkup; a loss of 10% is significant.
• A cat losing weight despite eating the same amount or more may have hyperthyroidism or diabetes. A cat drinking a lot may have kidney disease, diabetes, or hyperthyroidism.
• See a veterinarian promptly if the weight loss is sudden, your cat has stopped eating, or your cat is a kitten.
• Never give your cat medication intended for humans, even a common pain reliever.

How can you tell if a cat is losing weight in the hindquarters?

A thinning hind end reflects a loss of muscle mass, not just a loss of fat. The thigh and pelvic muscles help a cat jump and propel itself forward. They are often the first to shrink when a cat moves less or when an illness forces its body to draw on its protein reserves.

Prominent hips and less muscular thighs

Run your hand along your cat’s back toward the tail, then along the thighs. Compare what you feel with how your cat used to feel. These are signs of muscle loss:

• the hip bones and points of the pelvis are visible or clearly felt beneath the skin;
• the thighs are thinner and look hollow at the back;
• the base of the tail looks narrower;
• viewed from above, the hind end is narrower than the shoulders.

Changes in how your cat moves

Muscle loss also shows up in behavior. Your cat hesitates before jumping onto the couch, needs two tries, or stops climbing onto high furniture. Your cat comes down more slowly, its hind legs tremble while it stands, or its gait becomes stiff.

Weakness that appears suddenly is a different problem. If the hind legs suddenly become paralyzed, cold, or very painful, often accompanied by cries, it is an immediate emergency (a possible blood clot): go to the veterinarian without delay.

Keep in mind: muscle loss and excess weight are different things. An overweight cat may still have a round belly even when its thigh muscles have wasted away. If you only look at the scale or the belly, you can miss it.

Is it normal for a cat to lose weight in the hindquarters with age?

Only to a degree. A cat is considered a senior from 11 years of age. Sarcopenia is a gradual, age-related decline in muscle mass. Over the years, the body becomes less effective at building muscle, and an older, less active cat uses its hind legs less. In these cats, muscle loss is accompanied by weight loss that first affects the pelvis, hips, and hind legs.

A common mistake is to attribute all weight loss to age. In an older cat, weight loss often signals a disease, and most of these diseases respond better to treatment when caught early. Sarcopenia develops slowly, over months or years, and the cat continues to eat well, drink normally, and stay alert. Have your cat examined if you also notice any of these signs:

• a change in appetite, either an increase or a decrease;
• a water bowl that empties faster or wetter litter;
• vomiting, diarrhea, or a dull or poorly groomed coat;
• measured weight loss: a loss of 5% warrants a checkup, and 10% is significant. For a 4 kg cat, that is 200 g and 400 g.

In kittens, no muscle loss is “normal”: they should gain weight every week. A kitten that loses weight should be examined promptly by a veterinarian.

What diseases cause a cat to lose weight in the hindquarters?

The main causes are arthritis, chronic kidney disease, hyperthyroidism, diabetes mellitus, chronic digestive diseases, and intestinal worms. Appetite and thirst are often enough to point you in the right direction. The table below helps you sort through the possibilities before the appointment.

In older cats, appetite can also fall for reasons unrelated to a systemic disease, such as a painful tooth. Report any decrease in appetite, whatever its apparent cause.

Arthritis: less movement leads to muscle loss

Most cats over 12 years old have signs of arthritis visible on X-rays. Arthritis reduces an older cat’s activity and causes muscle loss in the hind legs: the hips and knees hurt, the cat jumps and plays less, and muscles that are no longer used waste away. Cats almost never have an obvious limp. Instead, their habits change: they sleep on the floor rather than up high, relieve themselves beside a litter box whose sides are too high, or develop mats in the fur on their lower back because they no longer turn to groom it.

Chronic kidney disease: more thirst and less appetite

It affects about one in three cats after 15 years of age. Damaged kidneys do not concentrate urine as well: the cat urinates more and compensates by drinking more. Waste products building up in the blood cause nausea, the cat eats less, and its body then draws on its muscles, starting with those in the hindquarters.

Hyperthyroidism: weight loss despite eating more

About 10% of cats over 10 years old have it. The thyroid gland produces too many hormones and speeds up the entire body, which burns more than it takes in: the cat loses weight despite a normal or increased appetite. The cat appears well, even more active, which often delays a veterinary visit. It is frequently accompanied by more meowing, especially at night, restlessness, vomiting, or loose stools.

Diabetes mellitus: increased thirst and a low gait

Diabetes mellitus causes weight loss and increased thirst in cats. Without effective insulin, cells can no longer take in sugar: it passes into the urine and takes water with it. Deprived of fuel, the body uses up its muscles. One sign directly affects the hindquarters: when diabetes damages the nerves, the cat walks with its hocks on the ground, “like a rabbit.”

Intestinal lymphoma and inflammatory bowel disease

In an older cat, repeated vomiting or chronic diarrhea accompanied by weight loss prompts an investigation for these two intestinal diseases. They look very similar: the veterinarian distinguishes between them with an abdominal ultrasound and, often, intestinal biopsies.

Intestinal worms, a common cause in young cats

Worms consume some of the food the cat eats and irritate its intestines. They mainly affect kittens, as well as cats that hunt or live outdoors. A round belly on a thin body, a dull coat, and loose stools should raise concern. In a young cat that loses weight despite deworming, the veterinarian also checks for feline infectious peritonitis (FIP) and the viral infections FeLV (feline leukemia) and FIV (feline AIDS).

What does the veterinarian do to find the cause?

The diagnostic process starts with the information you provide. The veterinarian weighs your cat and compares the result with previous weights. They assess muscle mass using a dedicated scale, the muscle condition score (MCS), which evaluates muscle independently of fat, then examine the entire animal: mouth, abdomen, joints, and heart. The basic tests are then:

• blood tests measuring creatinine, SDMA, and urea to assess the kidneys;
• total T4 to check for hyperthyroidism;
• blood glucose and fructosamine to check for diabetes (fructosamine reflects blood sugar levels over the preceding weeks without being skewed by the stress of the appointment);
• urinalysis with urine specific gravity to show whether the kidneys still concentrate urine and whether sugar is passing into it;
• fecal testing to check for parasites;
• blood pressure measurement, because blood pressure is often high with kidney disease or hyperthyroidism;
• X-rays if arthritis is suspected.

Your observations matter as much as the examination. Before the appointment, note:

• when you first noticed the thinning and whether it is getting worse;
• what your cat eats each day and whether that has changed;
• whether your cat drinks more and the litter is wetter than before;
• any vomiting, diarrhea, or changes in behavior or voice;
• the date of the last deworming treatment.

If you can, collect a little fresh urine or stool that morning: ask the clinic whether it would be useful.

Urgent: if your cat has stopped eating altogether, call your veterinarian the same day. A cat that goes without food for more than 2 to 3 days risks hepatic lipidosis, a rapid buildup of fat in the liver, especially if the cat is overweight.

What treatment helps a cat losing weight in the hindquarters?

Muscle returns when the underlying cause is treated. Adding more kibble without a diagnosis does not solve the problem. Treatment therefore depends on the disease found.

• Chronic kidney disease: a therapeutic kidney diet is part of treatment because it slows the disease’s progression. It can sometimes be less appealing, and its protein restriction needs monitoring in a cat that is already losing muscle: the veterinarian checks the cat’s weight and muscle condition score. Appetite improves mainly with prescribed treatments, including anti-nausea drugs such as maropitant and appetite stimulants such as mirtazapine. Transition to the new food over one to two weeks, gradually mixing it with the old food.
• Diabetes mellitus: treatment most often involves insulin injections along with an appropriate diet that is high in protein and low in carbohydrates; for some cats, the veterinarian recommends an oral treatment. Give the injection and the meal at the scheduled times every day. If your cat does not eat, call the veterinarian before giving the injection. When treated early, feline diabetes sometimes goes into remission: the cat no longer needs insulin as long as it stays on its diet.
• Arthritis: the veterinarian prescribes a veterinary anti-inflammatory drug such as meloxicam or robenacoxib, or a monthly injection of anti-NGF antibodies (frunevetmab), which blocks a pain messenger. At home, put a step or ramp by your cat’s favorite spots, choose a low-sided litter box, and play with your cat for 5 to 10 minutes twice a day to work its thigh muscles.
• Hyperthyroidism: there are four options. Thiamazole (methimazole), given as tablets or a gel applied to the ear, slows hormone production. Radioactive iodine destroys the diseased tissue in a single treatment. An exclusively fed low-iodine diet deprives the thyroid of its raw material. Finally, surgery removes the affected gland. Weight, appetite, and restlessness return to normal together. Treatment sometimes reveals kidney disease that had previously been masked, so the veterinarian monitors the kidneys during this period.
• Intestinal worms: deworm your cat with the product and at the frequency recommended by your veterinarian based on the cat’s age and lifestyle. Treat all the animals in the household at the same time.
• Sarcopenia: a quality diet suited to a senior cat and daily activity slow muscle loss.

Never give your cat medication from your own medicine cabinet. Some medications intended for humans are toxic to cats, including acetaminophen: a cat’s liver has great difficulty clearing it, and even a small amount can cause severe poisoning. Human anti-inflammatory drugs such as ibuprofen are also dangerous to a cat’s kidneys and stomach.

What should you do today if your cat is losing weight in the hindquarters?

Take these steps in order:

1. Weigh your cat using a kitchen scale or a baby scale accurate to 10 or 20 g, with your cat in a basket whose weight you subtract, or ask the clinic for a free weigh-in. Repeat at the same time of day every two weeks.
2. Measure how much your cat eats and drinks for three to five days: the amount served, the amount left over, and the water level in the bowl.
3. Watch your cat’s jumps, gait, and voice, and record anything that seems abnormal.
4. Make an appointment: within the week if the loss is gradual, in the following days if it is sudden, the same day if your cat has stopped eating, or within 24 hours if a kitten is eating less or has diarrhea.

Your records of weight, appetite, and thirst allow the veterinarian to see the progression instead of having to guess. To keep them in the same place as your cat’s deworming treatments and appointments, and to find the full history on the day of the visit: Download Papatte

Frequently asked questions