Frailty: An important emerging concept in veterinary medicine

The life expectancy of dogs and cats has increased due to advances in veterinary care and their growing role as family members.^1,2 As a result, veterinarians are seeing more aging pets. Aging is associated with an increased vulnerability to diseases such as neoplasia, osteoarthritis, and cognitive dysfunction, which negatively impact quality of life.³ As animals age, they lose robustness (the ability to maintain optimal physiological function) and resilience (the ability to recover from stressors).³

Definitions related to age matter. In dogs, the term senior denotes when they enter the last 25% of their lifespan. That number or chronological age varies because life expectancy is linked to size and weight.¹ Geriatric describes animals with multiple age-related physical and functional changes, and canine geriatric syndrome has been proposed to capture this presentation.³

Health span, the period of life an animal spends in good health and free of chronic disease and disabilities related to aging,⁴ should be prioritized over simply extending lifespan. Frailty is important to recognize and assess, as it negatively affects both health span and quality of life.⁴

Frailty is a well-established concept in human medicine and is recognized as a distinct clinical syndrome characterized by reduced functional reserve and physiological performance, leading to increased vulnerability to external stressors and adverse health outcomes.⁵ Frailty is not synonymous with disease. People and animals age differently, and biological age is more clinically relevant than chronological age. Frailty reflects biological age and is a stronger predictor of clinical outcomes, including postoperative morbidity, length of hospital stays, and mortality following anesthesia and surgery.⁶

Multiple instruments for identifying and quantifying frailty in humans have been published using 2 models: a frailty phenotype (FP) and a frailty index (FI).^7,8 The FP primarily focuses on physical decline and assesses 5 criteria: weakness (grip strength), self-reported exhaustion, slow walking speed, low physical activity, and unintended weight loss.⁵ A patient is classified as frail when 3 or more criteria are present.⁵ The FI model conceptualizes frailty as an accumulation of health deficits, with scores based on the number of comorbidities and, in some cases, laboratory data.

In veterinary medicine, both types of instruments have been explored in dogs and are well described by Adelman and Tarantino.^9.10 FI tools identify a broader picture of physiological decline but rely on extensive health information,^9,11 whereas FP tools contain components that are easily collected through observation of physical and behavioral changes.⁹ It has been proposed that the 2 models are complementary; FP instruments can be used for screening purposes by caregivers and FI tools by veterinarians to obtain a comprehensive clinical picture to direct intervention and decision-making.⁹

Because some criteria in human FP instruments require patient participation (eg, grip strength) and self-reporting, adaptations have been made to ensure applicability to veterinary patients. An FP comprising 5 objective criteria—weakness, slowness, endurance, physical activity, and weight loss—was developed using Labrador and golden retriever dogs 9 years and older.¹² Dogs were categorized as frail, prefrail, or nonfrail based on the presence of greater than or equal to 3/5, 1-2/5, 0/5 criteria, respectively, and their status (independent from chronological age) was predictive of all causes of death over a 5-year follow-up period.¹² This study documented that a frailty tool could be designed for dogs; however, it required equipment and resources that are not easily adapted to everyday clinical practice. This has led to the development of tools that can be readily used in clinical settings and in more heterogenous patient populations.¹³ 

Russell and colleagues developed an FP in a phase 1 study based on clinical examination and owner questionnaires and subsequently evaluated it in a phase 2 study of nearly 200 dogs of various breeds (56%), including mixed breeds (44%), aged 9.4 to 16.5 years.¹³ Dogs were recruited from different clinical services (oncology, internal medicine, cardiology, neurology, rehabilitation, and primary care).¹³ The 5 domains assessed were nutritional status, exhaustion, muscle weakness, social activity, and mobility, and dogs were categorized as frail or nonfrail. The FP was predictive of short-term (6-month) mortality, independent of age, sex, weight, and reason for presentation. The FP questionnaire and scoring guide can be downloaded from the online supplementary material on the publisher’s website.

If screening tools are incorporated into senior examinations, dogs at risk can be identified earlier, allowing interventions to slow or potentially reverse frailty. In one study, the prevalence of frailty was 42% in apparently healthy senior dogs.¹⁴ Ideally, frailty screening will become an integral component of clinical examinations, improving health span, lifespan, and quality of life in companion animals. 

Data from the Women’s Health and Aging Study indicate that earlier detection of frailty increases the likelihood that interventions will be effective.¹⁵ Weight loss, weakness, reduced physical activity, and impaired mobility—components of the frailty phenotype—result from the loss of muscle mass, strength, and function. Malnutrition and undernutrition have been identified as important contributors to frailty, underlining the need for nutritional intervention.^9,14 Increasing both the quantity and quality of dietary protein, along with optimizing ω-3 fatty acids (eicosapentaenoic acid and docosahexaenoic acid) intake, is recommended.¹⁶

The role of “muscle supplements” in delaying or reversing sarcopenia (age-related loss of muscle mass, strength, and function) and improving frailty scores remains unclear. A placebo-controlled study in beagles with moderate muscle loss reported that a dietary supplement containing ursolic acid improved functional performance, based on a 6-minute walk test and navigation of weave and jump obstacles.¹⁷ Muscle biopsies in treated dogs demonstrated inhibition of molecular mechanisms linked to muscle atropy.¹⁷ Therapeutic exercise represents another strategy to address decline in mobility, and functional scoring methods that guide rehabilitation plans and monitor response in aging dogs have been proposed.¹⁸ 

Frailty in cats has received less attention; however, a questionnaire that involved owners and veterinarians and includes both phenotype and index components has been developed and predicted 6-month mortality.¹⁹ The questionnaires can be downloaded from the online supplementary material on the publisher’s website.

Although frailty is a relatively new concept in veterinary medicine, the availability of clinical assessment tools paves the way for studies to explore which interventions work best to slow or reverse its progression, offering tremendous opportunities to improve the lives of companion animals.

References

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