Although promising new pharmacologic approaches to prevent and treat cachexia and sarcopenia are being developed, they are not yet available for clinical use in people or companion animals. However, in the meantime, the veterinary clinician still can address these 2 important syndromes in dogs and cats.
Diagnosis: The Importance of Enhanced Clinician Awareness
One of the keys to the management of cachexia and sarcopenia in dogs and cats is recognizing it in its earliest stages. To achieve this, BCS and MCS must be consistently assessed. The goal for BCS in a healthy dog or cat is 4–5 on a 9-point BCS scale. However, in certain diseases (eg, CHF, CKD), a slightly higher BCS may be desirable (ie, a BCS of 6–7/9), although further research is required to make specific recommendations. Even in animals with these diseases, obesity (BCS > 7/9) should be avoided.
The MCS differs from the BCS in that it specifically evaluates muscle mass.9,[121, 122] Evaluation of muscle mass includes visual examination and palpation of the head, scapulae, epaxial muscles over the thoracic and lumbar vertebrae, and pelvic bones. BCS and MCS are not directly related because an animal can be obese but still have substantial muscle loss (or conversely be very thin but have a normal MCS). Palpation is required for accurately assessing BCS and MCS, especially in animals with medium or long hair coats.
Cachexia should be anticipated in animals with chronic diseases such as CHF, CKD, cancer, and others. Consistently evaluating MCS in all patients will help identify muscle loss at an early, mild stage in aging or ill animals, rather than waiting until muscle loss is moderate or severe, when it may be more difficult to successfully manage. Similarly, as animals age, muscle loss is likely to occur, even in healthy individuals. Therefore, muscle mass should be thoroughly evaluated in geriatric cats and dogs.
For animals with chronic diseases in which weight or muscle loss is a component (eg, renal, cardiac, or hepatic failure; cancer; respiratory disease), it is critical to optimize medical treatment for the underlying disease. Specific recommendations for optimal diet (which includes the primary pet food, as well as treats, table food, and foods used for medication administration) should be an integral part of the overall medical treatment for all chronic disease conditions. In many cases, practical methods to help owners manage their animal's appetite are critical to success. This is particularly important because anorexia is one of the most common contributing causes to an owner's decision to euthanize his or her pet. Dietary modification, assisted feeding, or other feeding strategies often are beneficial in improving food intake and quality of life for these patients.
Any issues that potentially can affect food intake should be addressed, whether physical or environmental. Dental disease, for example, can substantially impair food intake in an otherwise healthy or sick animal. Pain (eg, back or joint) can decrease an animal's mobility and make it more difficult to secure adequate food intake. Environmental issues also can negatively impact food intake. Multipet households may impede the ability of an individual animal to gain access to food (eg, a more frail or timid animal may be crowded out from the food bowl). Stress often can increase for animals after diagnosis of cancer or CHF because of lifestyle changes (eg, medication administration, new foods), as well as increased stress on the part of the owner, which may be detected by the animal. An excellent website on environmental issues for dogs and cats is available for veterinarians and owners.
In addition to underlying medical issues and important environmental factors, the diet should be carefully evaluated. A brief nutrition screening should be performed in every patient at every visit, including a diet history, BCS, and MCS.[121, 122] For animals that have risk factors identified from the screening (eg, animals with medical conditions, geriatric animals, and those with altered BCS or MCS), a more thorough nutrition evaluation is required.[121, 122] The diet history often reveals important information that can then provide relatively easy, practical solutions. Clinicians should ensure that the diet being eaten by the animal is nutritionally complete and balanced. If owners are feeding a homemade diet, it is almost always nutritionally unbalanced (sometimes severely so) unless the diet was formulated by a board-certified veterinary nutritionist and the owner is carefully following the recipe. Even commercial dog and cat foods may be nutritionally unbalanced if the food label states “for intermittent or supplemental use only.” This is acceptable for veterinary therapeutic diets that are designed specifically to help manage diseases and are used under the supervision of a veterinarian. However, an over-the-counter diet should always be complete and balanced if it is fed in any substantial amounts to a dog or cat. In the United States, nutritional adequacy statement on a diet that is complete and balanced will be worded either as “(Name of product) is formulated to meet the nutritional levels established by the AAFCO [Association of American Feed Control Officials] Dog (or Cat) Food Nutrient Profiles” or “Animal feeding tests using AAFCO procedures substantiate that (Name of Product) provides complete and balanced nutrition for ··· (label regulations vary according to country).” Over-the-counter diets that are not nutritionally balanced may contribute to muscle loss (in a healthy or sick animal) and should be avoided. These diets also may not have an optimal nutritional formulation for the animal's underlying disease (eg, protein, fat, sodium, phosphorus).
The diet history also may reveal that the diet is unbalanced not because the animal is eating an unbalanced commercial food, but because of intake of a large proportion of calories from treats, rawhides, or “people food.” In this situation, even if the main diet is well-balanced, the other foods may be fed in a large enough proportion that the overall diet is unbalanced, which can contribute to weight and muscle loss as well as not being optimal for the underlying disease.
Determining the specific brand and flavor of the animal's main diet is important because it may reveal other factors that can contribute to cachexia or sarcopenia. For example, animals may be eating a diet that is relatively low in protein which will not be sufficient to maintain muscle mass in an animal with increased protein catabolism. Animals with CHF should not be fed a renal or otherwise reduced protein diet unless advanced concurrent CKD is present. Providing at least the AAFCO minimum for protein (5.1 g/100 kcal for dogs and 6.5 g/100 kcal for cats) is important, although higher dietary protein levels may be more optimal. Senior diets are highly variable in terms of their protein content (4.8–13.1 g/100 kcal for commercial senior dog foods in one study).
Commercial dog and cat foods also vary widely in calorie density, and because calorie information is not currently required on pet food labels (except for light or reduced calorie foods), it can be difficult for owners to realize that they may be inadvertently increasing or decreasing the daily calorie intake of their pets when they change from one food to another. One study found that the calorie density of senior dog foods ranged from 246 to 408 kcal/cup, and there are adult dog and cat foods available on the market now that are >600 or <250 kcal/cup. Therefore, it is important to ensure that undesired weight loss is not simply the result of switching to a lower calorie density food. It is also useful to be aware that senior diets not only vary in calorie density, but also in other nutrients that may be of importance in various diseases, including CHF and CKD. The sodium content in 37 senior dog foods, for example, ranged from 33 to 412 mg/100 kcal (the AAFCO minimum for sodium in dog foods is 20 mg/100 kcal).
Dietary supplement use is important to determine. Animals with diseases are more likely to be receiving supplements,[60, 61, 126] but owners typically do not volunteer this information unless specifically asked. Dietary supplements may contribute to muscle loss by causing anorexia or other adverse effects or by interacting with medications used to treat the underlying disease, thus decreasing their efficacy or increasing the adverse effects of the medications.
The preceding information emphasizes the importance of obtaining and evaluating a thorough diet history in animals with cachexia or sarcopenia. Board-certified veterinary nutritionists can be helpful in assisting the busy veterinary clinician by consultations in these situations.[127, 128]
Anorexia: Addressing Changes in Appetite
One of the most important issues for managing the anorexia that is often associated with cachexia and sarcopenia is to optimize medical treatment. However, appetite can remain a challenging issue despite optimal treatment of the underlying disease. Complete anorexia may not be present but owners often note changes in appetite, such as reductions in food intake, changes in food preferences, or “cyclical” appetite (ie, the animal will eat one food well for several days or weeks and then refuse it). A reduction in food intake in an animal that previously has been eating well may be an early sign of worsening of the underlying disease or a need for medication adjustment.
To address decreased food intake, client communication is important. Owners who are prepared for changes in appetite, both amounts and types of food, appear better able to deal with these changes effectively. The author typically provides a list (and samples) of several different commercial foods that meet the animal's nutritional needs based on the underlying disease and individual characteristics (eg, clinical signs, physical examination findings, laboratory results, and the individual animal and owner preferences). The owner then is instructed to feed one of the foods but to keep the others in reserve to try if appetite for the first food fails (although the animal often will eat that food again later). A nutritionally balanced, home-cooked diet formulated by a veterinary nutritionist also is an option, although these may be better reserved for later stages of disease to maintain more options as the disease progresses. Smaller, more frequent meals also may increase food intake, as can flavor enhancers (foods added to the dog or cat food to increase palatability). Flavor enhancers must be tailored to the disease (eg, high sodium flavor enhancers should be avoided in CHF, and high phosphorus and protein flavor enhancers, such as meat, fish, or cheese should be avoided in CKD). Cats typically prefer meat or fish type flavors, whereas dogs are more variable, with some preferring meat flavors and others preferring sweet flavors, such as yogurt, maple syrup, or applesauce. Animals with chronic diseases and even healthy aging animals often appear sensitive to food temperature and may have specific preferences. Thus, experimentation with foods at different temperatures may be helpful. Cats often prefer foods warmed but dogs may prefer food warmed, at room temperature, cold, or even frozen. Feeding the animal on a dinner plate, rather than the usual pet food bowl, or feeding in a different place in the house also may increase food intake. Modulation of cytokine production also can be beneficial for managing cachexia. Supplementation of the diet with fish oil, which is high in omega-3 fatty acids, can decrease inflammatory cytokine production and improve cachexia and food intake (see below).
Appetite stimulants (eg, mirtazapine, cyproheptadine) may benefit some animals with decreased or altered appetite, but it is important to carefully monitor body weight, BCS, MCS, and food intake to ensure adequate calorie intake. Owners (and veterinarians) often are mollified by some food intake, even if it is not sufficient to maintain weight or is not comprised of optimal diets or dietary components (eg, a cat with CKD that will only eat meat or a high protein, high phosphorous commercial food). In animals that continue to lose weight and muscle, despite the tactics suggested above, a feeding tube should be considered. Early tube placement is preferable to, and typically has a better outcome, than waiting until the animal is in end-stage disease with severe debilitation.
Omega-3 Fatty Acids
Increased dietary long-chain polyunsaturated omega-3 fatty acids, either from a highly enriched diet or through supplements, may have a number of benefits in animals with diseases that predispose them to cachexia or in animals with sarcopenia. Omega-3 fatty acids result in less potent inflammatory mediators (eicosanoids) than do omega-6 fatty acids, and omega-3 fatty acids also decrease TNF and IL-1 production. Omega-3 fatty acid supplementation has been shown to decrease the muscle loss in dogs with CHF and, in some animals, to improve appetite. In cardiac disease, omega-3 fatty acids have antiarrhythmic effects and also may enhance myocardial energy metabolism.[129, 130]
The optimal dosage of omega-3 fatty acids has not been determined, but the author currently recommends a dosage of fish oil to provide 40 mg/kg/day eicosapentaenoic acid (EPA) and 25 mg/kg/day docosahexaenoic acid (DHA) for animals with any degree of cachexia. Unless the diet is one of a few specially designed therapeutic diets, supplementation will be necessary to achieve this omega-3 fatty acid dosage. When recommending a supplement, it is important to know the exact amount of EPA and DHA in the specific fish oil brand because supplements vary widely. Fish oil supplements with good quality control should be used and they should always contain vitamin E as an antioxidant, but other nutrients should be excluded to avoid toxicities. Cod liver oil should not be used to provide omega-3 fatty acids at this high dose because it contains high concentrations of vitamins A and D which can result in toxicity. Flax seed oil or other plant-based omega-3 fatty acids also should be avoided because inefficient hepatic elongation of α-linolenic acid to EPA and DHA makes these inefficient (in dogs) or ineffective (in cats) sources of omega-3 fatty acids for these species. In addition, ventricular arrhythmias in dogs were not significantly decreased by flax seed oil supplementation, as they were with fish oil.
Exercise has been an effective method for helping to maintain muscle mass in people with cachexia and sarcopenia.[85, 132-135] There are differential effects of aerobic and resistance exercise in people. Although both have some benefits, resistance exercise appears to be particularly useful. For example, resistance training increases muscle mass in people but also can normalize some of the alterations seen in cachexia, such as reduced GLUT4 expression and increased myostatin concentrations. Exercise may be more challenging in some of the diseases associated with cachexia in dogs (eg, CHF) and particularly in cats, but exercise such as walking may provide an effective treatment for muscle loss in some diseases and in preventing sarcopenia in aging animals. Developing methods of resistance training for animals, such as electrical stimulation of the muscles, also may be beneficial.