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Weight Loss in Senior Cats

With feline obesity grabbing all the headlines these days, the serious implications of weight loss may be overlooked. 

 

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by Arnold Plotnick MS, DVM, ACVIM, ABVP

“He’s looking kinda thin lately”


Danny, a lovable 12 year old orange male tabby owned by Stephanie and Andres Lazerus, has an impressive medical history. Four years ago, he was diagnosed with diabetes. He was prescribed insulin and his diabetes quickly responded. Two years later he developed hyperthyroidism, a common glandular disorder of older cats. Oral medication was prescribed and his hyperthyroidism rapidly came under control. A year ago, miraculously, his diabetes went into complete remission and he no longer required insulin. Since then he’s been fed a low-carbohydrate diet, and his blood sugar has remained normal. Now he was in my exam room because lately, there’s been a little less of Danny to love.


Upon questioning, it was clear that Danny was doing fairly well otherwise. His appetite remained good, his thirst was normal, and there was no reported coughing, sneezing, vomiting, or diarrhea. On physical examination, however, he looked like the “after” photo in an imaginary feline weight loss advertisement. At his last visit, Danny was a robust 12 pounds. Today, he was down to 9 ¼ pounds despite his decent appetite. I recommended an initial battery of blood tests to try to figure out his cause of the weight loss. “We’ve been coming here for years. You know how we feel about Danny. Do whatever tests are necessary”, said Andrew. The hunt for a diagnosis was on.

Common Causes
There are many potential causes for weight loss in cats. Decreased food intake is an obvious cause, and poor appetite is a common concurrent complaint. Poor appetite and weight loss are general, vague clinical signs, however, and the list of possible illnesses is extensive. It narrows considerably when you consider the age of the cat. In a senior cat like Danny (cats aged 11 to 14 years) (see sidebar on feline life stages), weight loss is likely due to either a metabolic problem or a gastrointestinal problem. When a cat experiences weight loss despite a normal (or even an increased) appetite, the list of possibilities narrows even further.


The most common metabolic problems that cause weight loss in a senior cat are diabetes, hyperthyroidism, and chronic renal failure (CRF). Diabetes is one of the most common glandular disorders in cats, affecting about 1 in 400 cats in the United States. Diabetes occurs when the pancreas fails to produce adequate amounts of insulin, a hormone necessary for controlling blood sugar levels. Like Danny, most cats diagnosed with diabetes are over seven years of age, and males are almost twice as likely to become diabetic as females. Overweight cats are more likely to be afflicted.


Diabetes is usually easy to diagnose. Most cats present with the classic signs: excessive urination, excessive thirst, very good appetite, and weight loss. Danny was eating normally, but his thirst and urination were normal as well. Given his history of having had diabetes in the past, I had to see if he had relapsed. A complete blood count, chemistry panel, thyroid test and urinalysis were part of our initial work-up. “Most diabetics have an elevated blood sugar level, and have sugar in the urine. These are the first things we look for when making our diagnosis”, says Dr. Michael Stone, a veterinary internist at the Cummings School of Veterinary Medicine at Tufts University. I checked Danny’s blood and urine. The results were clear: Danny’s blood sugar was normal, and there was no sugar in his urine. Danny was not diabetic.


Hyperthyroidism is the most common glandular disorder in cats. It occurs when the thyroid gland in the cat’s neck produces an excessive amount of the thyroid hormone thyroxine (T4). It is seen mainly in senior and geriatric cats, the average age being around 12 or 13 years. “The most common clinical sign is weight loss”, notes Dr. Stone. “The next most common sign is ravenous appetite. A variety of other signs – excessive thirst and urination, vomiting, diarrhea, increased shedding, vocalization, restlessness – may or may not be present as well. “Hyperthyroidism is very treatable. In fact, it is curable. Hyperthyroid cats can be given an injection of radioactive iodine under the skin. The iodine travels to the thyroid gland where it disrupts the function of the thyroid cells, preventing them from releasing excessive amounts of T4. The T4 levels return to normal and the cat is cured. This treatment is safe but expensive, and can only be done at certain referral centers. A more common treatment involves administering the oral medication methimazole. This drug prevents the thyroid gland from releasing excessive amount of T4 into the bloodstream. It is not a cure. If the owner stops administering the drug, the thyroid gland will resume producing excessive amounts of T4, and the clinical signs will recur.


Diagnosing hyperthyroidism is usually easily accomplished by measuring the level of thyroid hormone in the bloodstream. Interestingly, Danny had been diagnosed with hyperthyroidism years before and was receiving his methimazole consistently. “Occasionally, a cat’s thyroid medication requirements will change, and some cats require an increase in dosage over time”, cautions Dr. Stone. Aware of this possibility, I measured Danny’s T4 level. It was right in the middle of the normal range. Poorly-controlled hyperthyroidism was not the cause of Danny’s weight loss.


Chronic renal failure (CRF) is perhaps the most common cause of weight loss in senior cats. Signs of kidney disease include increased thirst, excessive urination, weight loss, and vomiting. Cats with CRF, however, tend to have a poor appetite compared to diabetic cats and cats with hyperthyroidism; the latter often have increased appetite.


Diagnosis of CRF is usually made via blood and urine tests. The kidneys remove toxins from bloodstream and put them in the urine. When the kidneys fail, the toxin level will rise and the urine becomes dilute. Although Danny wasn’t showing any of the other common signs of CRF, the disease is such a common cause of weight loss in older cats that it behooved us to check. But Danny’s urine was adequately concentrated, and the level of kidney toxins in his blood stream was in the normal range. CRF was not the cause of Danny’s weight loss.


Going for the Gut
Having ruled out the familiar metabolic causes of weight loss in senior cats, I suspected a gastrointestinal (GI) cause. Two common GI disorders are inflammatory bowel disease and low-grade gastrointestinal lymphoma.
Inflammatory Bowel Disease (IBD) is an uncontrolled inflammatory response resulting in the infiltration of inflammatory cells into parts of the gastrointestinal tract. Although any age cat can be affected, most cats are middle aged or older. Not surprisingly, the most common symptom of feline IBD is weight loss. This may be accompanied by a decreased appetite, vomiting, or diarrhea. In most cats, physical examination of the GI tract tends to be normal, as was the case with Danny. Occasionally, thickened or fluid-filled intestines are evident when the abdomen is examined. Routine laboratory tests tend to be normal.


Gastrointestinal cancer can strike cats of any age, although it is mostly seen in older cats. The GI tract is susceptible to several types of cancer, however, low-grade lymphoma is the most common. The average age of affected cats is 9 to 13 years. The most common clinical signs are weight loss and decreased appetite. Vomiting occurs in about 50% of cases, and diarrhea in about 30%.


X-rays and ultrasound are common diagnostic procedures used to diagnose GI disease in cats. X-rays alone, however, are ineffective for diagnosing IBD or lymphoma. Increased intestinal wall thickness and enlarged abdominal lymph nodes may be visible on ultrasound in suspected cases of IBD and low-grade lymphoma, however these finding are merely suggestive, not diagnostic. Ultimately, a definitive diagnosis requires obtaining biopsy specimens from the GI tract.


Biopsies can be obtained either via endoscopy or exploratory surgery. Endoscopy is a procedure in which a long, flexible snake-like tube (the endoscope) enters the GI tract through the cat’s mouth (“upper GI endoscopy”) or anus (“lower GI endoscopy”) in order to visualize the internal lining of the GI tract and obtain biopsy specimens. Endoscopy is less invasive than surgery and allows for direct examination of the mucosal surfaces (innermost lining) of the GI tract. One limitation of endoscopy is that the biopsy specimens obtained by this method consist only of the mucosal lining rather than a full-thickness biopsy of the intestine, occasionally resulting in a misdiagnosis. Exploratory surgery allows the procurement of better biopsy specimens, although surgery is more expensive and more invasive. Both procedures – endoscopy and abdominal surgery – require general anesthesia.
Because I felt certain that Danny had a primary GI disorder, Danny’s owners elected to skip the ultrasound and proceed right to endoscopy. With no renal failure, no diabetes, and well-controlled hyperthyroidism, the anesthetic risk was minimal. Danny was scheduled for endoscopy the following day.


At endoscopy, the stomach looked normal, but the inner surface of the intestines had a pale, cobblestone type of appearance. Multiple biopsy specimens were obtained and Danny was awakened and sent home that evening. Two days later, the pathology report arrived. Danny had low grade intestinal lymphoma.


A Diagnosis and a Dilemma
Understandably, Danny’s owners were distraught upon hearing the diagnosis. I informed them, however, that although cancer is often a devastating diagnosis, the low-grade form of GI lymphoma is one of the more treatable feline cancers, and most cats show an excellent response to oral medications. Oral chemotherapy will not cure the condition, however. The chemo protocol most commonly prescribed for low-grade GI lymphoma consists of two drugs, prednisolone (commonly referred to in conversation as “pred”) and chlorambucil. The average survival time on these medications is around 25 months. Some cats fare better; others fare much worse.


Chlorambucil is usually well tolerated, however, a few cats will experience side effects. The most common adverse effects are GI toxicity and suppression of the bone marrow (the marrow is where the body manufactures red blood cells, white blood cells, and platelets). GI signs – vomiting, diarrhea, decreased appetite – are usually mild and resolve on their own.


Prednisolone is a steroid that also has the potential to cause side effects. Some cats will drink more water and urinate more when given pred. Others may show an improved appetite when given pred, which may be of benefit in those cats in which poor appetite was a major clinical sign of illness. A few cats, when given pred twice daily for long periods, become diabetic. This is where Danny’s dilemma arises. Danny, having been diabetic before, was at increased risk of becoming diabetic again if given pred. To avoid this, I chose to treat with chlorambucil alone and will evaluate whether he gains weight and goes into remission. If not, I may add prednisolone to the regimen and monitor closely. If he becomes diabetic, I may need to stop the drug, or we may once again need to give him insulin. “I’m glad we have a diagnosis, and that there’s a treatment”, says Stephanie. “He’s dealt with hyperthyroidism, and he’s dealt with diabetes. I’m sure he’ll be able to deal with this as well”.
I am, too.


Sidebar:
The Feline Advisory Bureau divides a cat’s life into six stages – kitten (0 to 6 months), junior (7 months to 2 years), prime (3 to 6 years), mature (7 to 10 years), senior (11 to 14 years) and geriatric (15 years and older).
 


 

        

Updated  5/13/10