Clinical Approach to the Cat that Is Losing Weight
World Small Animal Veterinary Association Congress Proceedings, 2019
C. Mansfield
Melbourne Veterinary School, University of Melbourne, Werribee, VIC, Australia

Ensuring a logical and step-wise process to work-up in a cat that is losing weight is vital to ensure that a timely diagnosis is made without excessive or expensive diagnostics. It is essential that a full and complete history is obtained, especially dietary history and a full physical examination is performed.

Weight loss in cats can often be tricky to detect, especially in cats with ventral fat pads, but frequent assessment and evaluation of the dorsal muscle tone is essential. The combination of history and physical examination will give you some major clues in your problem-solving approach and enable a quicker diagnosis to be made.

Step 1: Get the Right Information on Your Physical Examination and History

Establish if the Cat Has an Increased or Decreased Appetite

If the cat can’t or won’t eat, there may be a physical reason for this such as oral/dental pain or a biochemical reason such as uraemia causing suppression of appetite. A thorough examination of the oral cavity is required, as well as further questioning of the way the cat eats is important. If the cat attempts to eat food but cannot prehend or chew, then oropharyngeal disease is more likely. If the cat asks for food, but then appears to refuse the food once offered, then anticipated pain due to oesophageal or intestinal disease may be present.

If the cat is eating more than normal, then some degree of maldigestion/malabsorption (i.e., intestinal or pancreatic disease) may be present, or there may be loss of nutrients (diabetes mellitus) or excessive utilisation of nutrients (hyperthyroidism).

Establish if the Cat Is Drinking or Urinating More than Normal

This goes hand in hand with the information above. For example, a cat that is losing weight with an increased appetite and polydipsic/polyuric is more likely to have diabetes mellitus than other disease. Sometimes it may be difficult for owners to determine this, but they may notice the cat drinking out of more unusual places that normal.

Establish if There Are Any Gastrointestinal Signs

For some owners, vomiting is considered a normal event in cats. However, vomiting even as infrequently as once every 2 weeks in combination with weight loss may increase the index of suspicion. Therefore, it is important to specifically ask owners this question, along with determining if there have been any loose stools or other clinical signs.

Look for Localising Signs on the Physical Examination

As mentioned above, this may include evidence of oral or periodontal disease in a cat that is unwilling to eat. Other parts of the physical examination that should carefully attended to include the thyroid area (assessing for goitre), abdominal palpation (for lymph nodes and intestinal thickness) and the size of the kidneys. Again, each of these will help refine the problem list and move on to the next step.

Step 2: Determine the Laboratory Tests You Want Initially to Run

Based on the problem list and differential diagnosis, it is highly likely that the differentials will be reduced to a small number. The body systems that are of concern may be the endocrine (hyperthyroidism, diabetes mellitus), renal or intestinal (including oral pathology). Generally, for most cats with weight loss it is usually important to perform haematology and serum biochemistry along with urine analysis to evaluate for kidney function and diabetes. Most external laboratory panels will include serum thyroxine (T4), but if not, this should also be performed. A urine to protein creatinine ratio may be useful if there is evidence of protein on the initial urine analysis. In the initial stages there is usually no indication to measure feline pancreatic lipase immunoreactivity. If the cat has diarrhoea and poor worming history, then faecal testing may be indicated prior to, or alongside, blood testing.

Step 3: Support the Cat Whilst Waiting on or Running Diagnostics

Serum cobalamin is absorbed in the ileum of cats, and so cats with intestinal disease are likely to have cobalamin deficiency. It has been shown that cobalamin supplementation improves clinical signs in cats with GI disease regardless of the underlying cause. It is advisable to measure serum cobalamin if feasible, but if not, then the empirical dosage is 250 µg by injection once weekly for four weeks.

Intravenous fluid therapy should be administered if there are signs of dehydration, and careful attention to electrolyte deficits paid. If the cat is unwell and has not been eating, then a feeding tube should be considered. This is very important to prevent development of hepatic lipidosis as well as improve the nitrogen balance in unwell cats. If there is no coagulopathy then an oesophageal feeding tube is easily placed, but as this requires a general anaesthetic should be combined with other diagnostic testing. The resting energy requirement (RER) for the cat’s current weight should be calculated (40xBW) and feeding gradually increased up to that amount (i.e., 25% first day, 50% second day, 75% third day, 100% fourth day). The exact food to be fed depends on their clinical status and suspected underlying disease, however all the essential amino acids for cats should be provided.

Step 4: Decide Whether to Investigate Further

If a diagnosis has been reached by this stage, then there is usually no indication to proceed further with investigations unless further staging is required. The main differential diagnoses remaining after exclusion of extra-gastrointestinal disease and oropharyngeal disease include pancreatitis, inflammatory bowel disease, alimentary lymphoma, exocrine pancreatic insufficiency, and other rare causes of intestinal and/or central disease.

If the cat is sick enough to require fluid therapy or interventional nutrition, and there is no diagnosis reached on the initial blood work, then further investigation is warranted. This would generally start with abdominal ultrasound to assess the intestinal tract, pancreas, liver and mesenteric lymph nodes. If any abnormality is seen, then fine needle aspirates should be obtained (and consideration to culture the bile should be considered). As mentioned above, if interventional nutrition is indicated then a feeding tube should be inserted at the same time. If no diagnosis is reached with this relatively “hands-off” approach, then biopsy of the intestinal tract and/or other abdominal organs should be considered. Either endoscopy or exploratory laparotomy could be considered, again targeted towards the main differential diagnosis.

If the cat is relatively well, then trial treatment could be considered, and exocrine pancreatic insufficiency ruled out prior to further investigation. In comparison to dogs, dietary therapy in these cases is challenging if the cats have a reduced appetite. However, dietary modification is very important in cats with chronic GI disease, and even more so if there is concurrent pruritis, as there is an increased index of suspicion for food sensitivity.

In one study, 50% of cats with chronic GI disease were food responsive, with a substantial subset of them not relapsing when re-challenged with their previous diet. Even cats with severe clinical signs may respond to dietary treatment alone, and so this should be the first step in targeted treatment. Response to diets typically occurs within 1–2 weeks. Diets generally consist of hydrolysed or novel protein sources and contain a moderate amount of soluble fibre. If diarrhoea is present, then the use of probiotics or synbiotics may be of some benefit as well.

If cats are not dietary responsive or there is evidence of liver involvement on the initial blood tests, then antibiotics could be considered. If the cat has evidence of hepatic encephalopathy or is very sick then the antibiotics should be given intravenously. If on investigation it is suspected that there is an infectious cholecystitis, then ideally the choice of antibiotics should be based on culture results.


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4.  Hart ML, Suchodolski JS, Steiner JM, Webb CB. Open-label trial of a multi-strain synbiotic in cats with chronic diarrhea. J Feline Med Surg. 2012;14(4):240–245.


Speaker Information
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C. Mansfield
Melbourne Veterinary School
University of Melbourne
Werribee, VIC, Australia

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