How to identify the cause of weight loss in geriatric cats
Weight loss occurs when more calories are expended than are consumed. Healthy animals can experience weight loss, but in a geriatric cat, a subtle decrease in weight can also be the first indication of illness. For example, cats with small intestinal disease may lose weight before exhibiting anorexia, vomiting, or diarrhea. Unfortunately, weight changes in older cats are often attributed merely to aging, so clients may not seek veterinary care or veterinarians may inadvertently delay a diagnostic workup until marked weight loss is evident or additional clinical signs arise. Starting with a detailed history, work your way through a complete workup in these patients.
ASK ALL THE RIGHT QUESTIONS
The answers to these questions may reveal important clues about the cat's weight loss. For example, in some households, pets compete for food, and underfeeding results. Clients may feed a weight-loss diet and continue it even after an optimal weight has been achieved. An arthritic or visually impaired cat may not be able to make it to food bowls that are difficult to access, such as on a countertop or in a dark basement. And an inability to smell food, the administration of certain medications, or a systemic illness can result in a decreased appetite, even in cats being fed a high-quality, palatable food.
Remember to ask about travel history; feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) testing, exposure, and vaccination history; environmental exposures (e.g. second-hand smoke, herbicides); prior anesthesia; and any medications being given. Many medications can cause gastrointestinal (GI) distress. Common examples are nonsteroidal anti-inflammatory drugs, glucocorticoids, chemotherapeutics, fluoroquinolones, amoxicillin, ACE inhibitors (e.g. benazepril, enalapril), and digoxin. Medications (notably doxycycline), improper medication administration, and reflux into the esophagus during anesthesia may cause esophageal stricture.
Vomiting in cats may be clinically relevant even if the owner reports that it occurs only once a month. Also, a lack of vomiting does not rule out GI disease; cats can compensate for small intestinal disease by absorbing more fecal water in the colon, resulting in normal-appearing stools. Some cats with GI lymphoma, for example, show only weight loss, with little or no vomiting or diarrhea. In cats with heartworm disease, a common presenting complaint is chronic vomiting.
Be sure to try to differentiate vomiting from regurgitation, based on the presence or absence of abdominal contractions and bile or digested blood in the material brought up and on the shape and degree of digestion of the food. Even with a thorough history, it can be difficult to differentiate vomiting from regurgitation. In these cases, use pH paper to determine the pH of the material. If it is acidic, the material is of gastric origin and vomiting is confirmed. Regurgitated material tends to be neutral.
Polyuria and polydipsia
A history of polyuria and polydipsia can indicate many disorders, including hypercalcemia, diabetes mellitus, renal and hepatic disease, disorders affecting potassium and sodium concentrations, pyometra and other infections, hyperthyroidism, and polycythemia, as well as with the administration of certain medications (e.g. corticosteroids, diuretics).
Asking about lameness may help you identify diabetic neuropathy, hypertrophic osteopathy, arthropathies, and neoplastic involvement of bones. Lameness may be the presenting problem in cats with primary pulmonary neoplasia since bronchoalveolar carcinoma frequently metastasizes to the digits (and tail). If you do not ask about subtle lameness during the history, lameness may not be identified since cats are often reluctant to walk in the examination room and swelling or increased warmth of joints may not be detectable on physical examination. A decreased jumping ability may occur in cats with diabetic neuropathy because of hindlimb weakness and ataxia and vision problems. Diabetic neuropathy may also cause a plantigrade stance.
Neurologic and dermatologic changes
Yawning that is more frequent or is inappropriate for the situation, changes in mentation or behavior, ataxia, or seizures may be associated with intracranial disease. Cats with hyperthyroidism may show increased activity, increased vocalization, increased grooming, or an unkempt coat. Pruritus may occasionally result from cholangiohepatitis or other liver disease or as a paraneoplastic syndrome.2
EXAMINE FROM NOSE TO TAIL
After obtaining a complete history, perform a thorough physical examination in every cat presenting with weight loss. Be sure to record the cat's weight and body condition score.
Palpate all cats older than 6 years for thyroid gland enlargement. Occasionally, the thyroid gland may be cystic, and an enlargement is not diagnostic for hyperthyroidism. Parathyroid gland enlargement from renal secondary hyperparathyroidism may be mistaken for thyroid enlargement.
Neoplastic involvement of a lymph node can present with a subtle change in size or firmness of only one lymph node, so carefully palpate all peripheral lymph nodes (Figure 1), and obtain needle aspirates of any suspicious nodes for cytologic examination. A palpably normal node does not rule out neoplastic infiltration. Cytology is more sensitive for detecting neoplastic involvement than is palpation and should be performed whenever lymph node involvement is a concern.
When auscultating the chest, listen to the lungs before the heart. It is my clinical impression that listening to the louder heart sounds first decreases the ability to detect the softer lung sounds. Tachypnea may be related to stress from transport or being in the clinic, so ask the owner about the cat's breathing rate and rhythm at home. Allow the cat to relax in the room before taking its temperature and evaluating its respiratory and heart rates. Dyspnea should prompt a search for intrathoracic and upper respiratory disease.
A murmur may be auscultated in patients with severe anemia, hyperthyroidism, hypertension, or primary cardiac disease. Sinus bradycardia can occur with intestinal obstruction, hyperkalemia, or increased intracranial pressure from central nervous system disease. Cardiac cachexia is uncommon in cats, but when it is present it is usually associated with severe, chronic, right-sided congestive heart failure.3 Tachycardia may occur with hyperthyroidism, primary cardiac disease, fever, anemia, sepsis, hypoxia, or stress. Gently compress the cat's chest to assess compressibility. Decreased compressibility and decreased resonance on thoracic percussion may occur with mediastinal masses or pleural effusion.
In cats with pancreatitis, abdominal tenderness sometimes is noted. Most cats with pancreatitis probably have pain that is unrecognized by the practitioner and owner. Bilaterally small, hard, and irregular kidneys may be palpated in cats with chronic renal failure. Enlarged and irregular kidneys may be encountered with renal feline infectious peritonitis, neoplasia, or polycystic disease.
Placing a cat on its back may make an intra-abdominal mass more prominent visually and on palpation. Applying pressure to various locations on the abdomen while a cat is on its back can also help you localize a painful site. V-trough pet positioners and towels can comfortably position cats for such examinations (Figure 2).
Note the patient's mentation. If you suspect a neurologic disease, you may elicit a positional nystagmus or strabismus by placing the patient on its back and extending the neck.
Always perform a complete ophthalmic examination in geriatric cats, as signs of systemic disease such as anisocoria, detached retinas, or abnormalities of the fundus may be seen. Similarly, a general physical examination should be done on a cat presented for ophthalmic disease.
EVALUATE INITIAL DIAGNOSTIC TEST RESULTS
Once you've ruled out inadequate food intake unrelated to illness (e.g. because of competition, an inability to get to food, an unpalatable diet), try to determine what body systems are affected. The history and physical examination findings will help to localize your search. For example, if a cat that has a history of chronic intermittent vomiting is now experiencing weight loss and anorexia and if thickened intestinal loops are noted on examination, primary GI disease is likely.
Perform a complete blood count (CBC), a serum chemistry profile, a serum thyroxine (T4) concentration measurement, a urinalysis, and a fecal examination. It is often a good idea to keep some extra serum frozen for possible additional diagnostic tests. Measure blood pressure in cats more than 10 years old. Perform FeLV and FIV testing if the status isn't known or the history warrants it. Heartworm testing may also be indicated.
Complete blood count
The CBC may indicate eosinophilia associated with inflammation of the intestinal tract, hypereosinophilic syndrome, enteric parasites, or heartworm disease. If anemia is identified, determine whether it is regenerative or nonregenerative, based on a reticulocyte count. Cats with chronic kidney disease may have a mild nonregenerative anemia or severe anemia. A microcytic, hypochromic anemia indicates iron-deficiency anemia from chronic blood loss, which may be observed with bleeding GI tumors. Uremia may also cause bleeding from microulcerations. Uncommonly, bleeding may occur with severe intestinal disease, apparently caused by vitamin K malabsorption.5 Always determine the FeLV and FIV status in anemic cats.
Serum chemistry profile
An elevated blood urea nitrogen (BUN) concentration with a normal creatinine concentration can be caused by early prerenal azotemia, a high-protein diet, drugs (e.g. tetracycline, corticosteroids), and fever. It may also indicate GI bleeding and subsequent intestinal absorption of the blood. If the creatinine concentration is also elevated, consider chronic renal failure.
Hypoalbuminemia may indicate renal disease, liver disease, hemorrhage, malassimilation (maldigestion and malabsorption), hyperglobulinemia, exudative cutaneous disease, or protein-losing enteropathy. A decrease in both the albumin and globulin concentrations is consistent with intestinal loss. Severe hypoalbuminemia (< 2 g/dl) with diarrhea suggests protein-losing enteropathy. Cats with protein-losing enteropathy usually have GI lymphoma or inflammatory bowel disease.
Hyperglobulinemia can be seen with neoplasia and chronic inflammation. When the hyperglobulinemia is moderate (5 or 6 g/dl) or severe (> 6 g/dl), consider protein electrophoresis to determine whether a monoclonal or a polyclonal gammopathy is present. A monoclonal gammopathy is more consistent with lymphoma, plasma cell tumors, and multiple myeloma.
A low serum cholesterol concentration (< 150 mg/dl) may be seen with protein-losing enteropathy, hepatopathy (cirrhosis), and malassimilation.
Increased serum liver enzyme activities may be noted with either primary liver disease or a reactive hepatopathy. Common causes of increased liver enzyme activities include hepatic neoplasia, pancreatitis, cholangitis from bacteria that presumably originate from the intestines, hepatic lipidosis, and cholangiohepatitis. Normal enzyme activities do not rule out liver disease. In cats with cirrhosis, liver enzyme activities may be normal because of decreased functional hepatocellular mass and a subsequent decrease in liver enzyme production. Alkaline phosphatase (ALP) activity is not usually increased in cats with hepatic tumors, probably because its serum half-life is short. Gamma-glutamyltransferase (GGT) has greater sensitivity than ALP does for feline liver disease, except in cases of hepatic lipidosis.6 An increase in ALP without a concurrent increase in GGT is consistent with hepatic lipidosis.
An increased bilirubin concentration may occur with hepatobiliary disease and hemolysis. Hemolysis must cause a rapid and marked drop in red blood cells to produce clinical icterus. Icterus is usually not detectable in the sclera until the serum bilirubin concentration is > 3 mg/dl.
If hepatic disease is suspected, measure fasting and postprandial serum bile acid concentrations to confirm liver dysfunction. If a hepatopathy is suspected, remember that cholangiohepatitis, pancreatitis, and intestinal disease frequently occur together in cats and are referred to as triaditis. Assessing amylase and lipase activities is not helpful in diagnosing clinical pancreatitis in cats.7
Hypercalcemia may occur with renal disease, paraneoplastic syndrome (e.g. lymphoma, squamous cell carcinoma), idiopathic hypercalcemia, primary hyperparathyroidism, and laboratory error (which is the most common cause and can occur with lipemic and hemolyzed blood samples). Hypercalcemia of malignancy is rare in cats.8 Cats do not have a linear relationship between serum total calcium and albumin concentrations and the total protein concentration, so do not adjust the calcium concentration based on the albumin concentration. Evaluating concentrations of ionized calcium, parathyroid hormone, and parathyroid-related protein (a substance released by cancer cells that mimics the effects of parathyroid hormone) can help identify the cause of hypercalcemia.
A cat is hypoglycemic if its blood glucose concentration is < 60 mg/dl. The most common causes of hypoglycemia are liver failure, sepsis, prolonged sample storage, and iatrogenic causes (e.g. insulin therapy). Increases in blood glucose concentration should be interpreted with knowledge of the urine glucose concentration. Because hyperglycemia may be transient or caused by stress, if there is doubt about the cause of the hyperglycemia obtain a serum fructosamine concentration to assess the average blood glucose concentration over the preceding two to three weeks.
Serum T4 concentration
Nonthyroidal illness may decrease the serum T4 concentration into the normal range, or even below normal, in a hyperthyroid cat. More severe illnesses tend to be associated with lower T4 values.9 Additional testing, such as a free T4 by equilibrium dialysis, may be needed if you suspect hyperthyroidism, even with a normal serum T4 concentration.
Performing a urinalysis at the same time as the CBC and serum chemistry profile reveals a wealth of information. You can detect diabetes mellitus, inadequate urine concentrating ability, ketonuria, proteinuria, hematuria, crystalluria, ongoing renal tubule damage, and a bacterial urinary tract infection. A suboptimal urine concentration may be present with acute or chronic renal insufficiency or failure, pyelonephritis, hyperthyroidism, diabetes mellitus or diabetes insipidus, or polydipsia caused by the reasons mentioned earlier.
Urine protein:creatinine ratio
Protein loss into the urine may cause chronic weight loss. Proteinuria should prompt a thorough evaluation for an underlying cause. If indicated, request a urine protein:creatinine ratio; normal is < 0.5. Glomerulonephritis can occur secondary to chronic infectious, inflammatory, and neoplastic conditions. Glomerulosclerosis can occur secondary to diabetes mellitus, hyperfiltration, and hypertension. Preglomerular proteinuria can occur from increases in the serum protein concentration (> 9 g/dl).10
Urinary tract infections can be occult (without pyuria or hematuria) with diseases or medications, such as glucocorticoids, that suppress the inflammatory response and immune system. Older cats are also more prone to urinary tract infections because of immune system senescence and inadequate urine concentrating ability. Urine, obtained by cystocentesis, should be submitted for bacterial culture and antimicrobial sensitivity testing.
Even when the results of a fecal examination (flotation and direct smear) are negative, empirical deworming is often appropriate.
Acholic (i.e. gray, clay-colored) stools can be seen with exocrine pancreatic insufficiency and nonsuppurative cholangitis-cholangiohepatitis. The latter can produce intermittent acholic stools, and it may be appropriate to have the owner bring in five consecutive days of stools in a cat with other signs of this disease, such as chronic elevation of liver enzyme activities, increased appetite, or hepatomegaly.
Blood pressure measurement
Blood pressure measurement is an underused diagnostic tool, but it is becoming a standard of care in veterinary medicine. Systemic hypertension is a systolic blood pressure ≥ 160 mm Hg. Diseases associated with hypertension in cats include chronic or acute renal failure, hyperthyroidism, diabetes mellitus, and neurologic disease. Intracranial disease increases systemic blood pressure as a compensatory mechanism.
Increased age increases the risk for hypertension, particularly because renal insufficiency and hyperthyroidism are more common in elderly cats. All cats more than 10 years old should undergo routine screening for hypertension.11 Using 10 years of age as a guideline for beginning the routine monitoring of blood pressure can be supported by studies of hypertensive cats. In a study of 69 cats with hypertensive retinopathy, 64 (92.7%) were older than 10 years,12 and in another study of 58 cats with hypertension, 84% were older than 10.13
The results of initial diagnostic tests may indicate that other diagnostic tests such as radiography, pancreatic immunoreactivity tests, cobalamin and folate measurement, and fecal alpha1-protease inhibitor measurement are needed. Ultrasonography, cytology, histology, and endoscopy or laparoscopy may also be warranted.
Thoracic and abdominal radiography is often needed after routine laboratory testing and helps to identify masses, organomegaly, fluid accumulation, or calcified areas (e.g. uroliths, nephroliths, intestinal cancers, choleliths). Choleliths may be occasionally seen with cholangitis-cholangiohepatitis complex and chronic pancreatitis. An enlarged sternal lymph node may be seen with abdominal inflammatory or neoplastic disease, since this lymph node drains portions of the abdomen. Poor abdominal radiographic detail can result from fluid accumulation, carcinomatosis, or a lack of body fat.
Pancreatic immunoreactivity tests
Measuring fasting trypsin-like immunoreactivity (TLI) and pancreatic lipase immunoreactivity (PLI) is often indicated to diagnose GI disease and has become fairly routine in some practices.* Exocrine pancreatic insufficiency is diagnosed by identifying decreased TLI concentrations. Although diarrhea usually occurs in cats with exocrine pancreatic insufficiency, it may not always be observed in cats that eliminate outdoors; weight loss may be the only reported clinical sign.
PLI is the preferred blood test for diagnosing feline pancreatitis. Compared with TLI, it is more sensitive and specific,14 and serum PLI concentrations stay elevated for much longer.15 PLI is also more accurate than ultrasonography.14 If the PLI concentration is normal, moderate to severe pancreatitis can be confidently ruled out, and an elevated PLI will accurately diagnose feline pancreatitis about 90% of the time.14
Cobalamin and folate measurement
Measuring the serum cobalamin (vitamin12) concentration is recommended in cats with chronic GI disease.* Because adequate serum cobalamin concentrations depend on normal pancreatic protease activity and normal absorption by binding to specific receptors in the ileum, cobalamin deficiencies may be found with chronic disorders of the distal small intestine and with exocrine pancreatic insufficiency.16 Because cobalamin is required for metabolism, cobalamin deficiency may contribute to the clinical signs of GI disease and lead to suboptimal response to treatment of the primary disease.
Increased serum folate concentrations* can be a sign of small intestinal bacterial overgrowth because bacteria in the small intestine produce folic acid, which is then absorbed into the bloodstream.
Fecal alpha1-protease inhibitor measurement
Fecal alpha1-protease inhibitor is a protein that can be measured in feces to detect excess protein loss through the GI tract.* In a study of nine cats with chronic GI disease, eight had increased fecal alpha1-protease inhibitor concentrations.17 The sample should be collected through defecation, not digitally. In a study performed in dogs, most digitally collected samples had increased alpha1-protease inhibitor concentrations compared with samples spontaneously voided, probably because of trauma to the rectal mucosa and resultant leakage of the protein.18
Ultrasonography is commonly performed in patients with weight loss. Evaluate the patient for normal echogenicity of organs relative to each other (e.g. the spleen should be more echogenic than the liver, which should be greater or equal in echogenicity to the renal cortices); masses; bladder, kidney, or gallbladder stones; lymph node enlargement; cystic structures; increased organ size or thickness of GI wall layers; apparent discomfort with transducer pressure; and regional or generalized free abdominal fluid.
I recommend attempting to image the pancreas in every patient undergoing abdominal ultrasonography, regardless of the presenting problem, to learn to identify the pancreas and recognize the variability in the normal pancreas. A width of greater than 1 cm in a ventrodorsal dimension for the left limb of the pancreas is suspicious for pancreatic enlargement in cats. In a study of 84 cats, the obtained 95% reference interval for this dimension was 2.6 to 9.5 mm,19 and the size and echogenicity of the pancreas did not change with age.19 The diagnostic accuracy of ultrasonography in diagnosing feline pancreatitis is variable. Normal ultrasonographic findings do not rule out pancreatitis in cats because the disease may only be identifiable microscopically and may be focal to multifocal. Neoplastic infiltration, such as occurs with lymphoma, is also a differential diagnosis for ultrasonographic pancreatic abnormalities.
Increased intestinal wall thickness (> 3 mm in cats) or decreased distinction of the wall layers can be seen with infiltrative disease, such as inflammatory bowel disease or lymphoma. However, ultrasonography is not sensitive for diagnosing diffuse infiltrative disease, so a normal ultrasonogram doesn't rule out infiltrative GI disease. It is my impression that palpation is more sensitive for diagnosing increased intestinal wall thickness than is ultrasonography, especially if the patient is thin.
Cytologic and histologic examination
Collecting fluid or cellular material by fine-needle aspiration or collecting tissue by needle or surgical biopsy for cytologic or histologic examination may be required to obtain a definitive diagnosis in a cat with weight loss. Fine-needle aspiration usually poses little risk, and cytologic analysis of obtained samples can diagnose lymphoma, mast cell tumors, some carcinomas, infections, and hepatic lipidosis. Assess the patient's coagulation status, especially before performing a liver biopsy, and carefully consider the limitations, risks, and benefits of obtaining samples from various organs. Aspirate free abdominal fluid as close as possible to the suspected primary lesion for the best chance of obtaining a diagnostic sample. For example, if liver disease is suspected and fluid is seen both between the liver lobes and near the urinary bladder, the aspirate should be taken near the liver.
In cases of suspected bacterial cholangitis and cholangiohepatitis, ultrasound-guided transhepatic cholecystocentesis can be done to obtain bile for cytology and aerobic and anaerobic cultures. Deflating the gallbladder by removing most of the bile during aspiration reduces the risk of leakage. The procedure is not recommended when necrotizing cholecystitis or extrahepatic biliary obstruction with a severely distended gallbladder is suspected. A gallbladder wall thickness of greater than 1 mm is an indication of gallbladder disease, but an ultrasonographically normal gallbladder does not rule out disease.
Pancreatic neoplasia, pancreatitis, and focal septic peritonitis cannot be differentiated ultrasonographically. To make a definitive diagnosis, perform a cytologic examination of a fine-needle aspirate. Fine-needle aspiration can also diagnose pancreatic pseudocysts. Since obtaining biopsy samples of the pancreas rarely causes pancreatitis, fine-needle sampling is considered a low-risk procedure.
Endoscopically obtained GI biopsy samples are likely to be diagnostic in cats, provided the samples are obtained from the proximal small intestine (or duodenum) and not just the stomach. Most cases of alimentary lymphoma in cats involve only the small intestine, and pockets of lymphocytes occur in the villi from which biopsy samples can be easily obtained endoscopically. In one report when alimentary lymphoma was present in cats that ranged in age from 6 to 18 years, endoscopic biopsy was used to obtain the diagnosis in more than 90% of the patients.4
Laparoscopy has several advantages over other diagnostic procedures. It allows you to obtain large biopsy samples and is particularly useful for liver biopsies. Small lesions on peritoneal surfaces can be difficult to visualize on ultrasonographic examination, but lesions < 1 mm in diameter can be seen with laparoscopy. The ability to see small lesions can be used to diagnose and stage abdominal neoplasia. The pancreas, which can be particularly difficult to image, can be visualized and biopsied safely with laparoscopy.
Weight loss is commonly noted in geriatric cats. A thorough history and physical examination will usually reveal valuable clues as to the most likely causes. But even if weight loss is the only abnormality identified, a complete diagnostic workup is often indicated. Early diagnosis can prevent further weight loss and the development of other clinical signs as well as improve a patient's response to therapy.
*Samples for TLI, PLI, cobalamin, folate, and fecal alpha1-protease inhibitor measurement can be submitted directly to the laboratory that performs the assays or to your usual laboratory that then forwards the samples. The laboratory that performs these assays is the Gastrointestinal Laboratory, 4474 TAMU, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4474; phone (979) 862-2861; fax (979) 862-2864; www.cvm.tamu.edu/gilab.
Anne Mattson, DVM, MS, DACVIM
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