WHAT IS AGING?
How we define aging depends on our goals and our frame of reference. From the biomedical perspective of the veterinary clinician, the important elements are:
- The passage of time
- Deleterious physiologic and functional changes at the molecular, cellular, tissue, and organismal levels
- A progressive increase in the risk of the three Ds
- Disability
- Disease
- Death
As cats age, they lose robustness (the ability to maintain a state of baseline or optimal physiologic function in the face of external stressors) and resilience (the ability to return to this state following perturbations caused by such stressors).1 This leads to frailty and the development of many age-associated diseases which seem superficially unrelated but which are actually all consequences of the same underlying mechanisms of aging.2
IS AGING A DISEASE?
Because aging is a universal phenomenon, at least in mammals, and because historically there have been no effective interventions to slow or stop the aging process per se, only treatments to mitigate the clinical consequences, aging is widely seen as natural, inevitable, and immutable. However, decades of foundational research in laboratory model species, and more limited recent studies in humans and other species, suggest that the core mechanisms of aging can be altered in a way that may prevent the health consequences of aging. Much debate has focused on the semantic issue of whether or not something natural and ubiquitous but also responsible for illness and death should be labeled a disease.3 There is not yet any consensus resolution to this debate.
A pragmatic approach that avoids this semantic debate is to view aging is the most important modifiable risk factor for disease in companion cats. This is a familiar concept to veterinarians. Obesity, for example, is a risk factor for multiple specific diseases overall mortality hazard.4–6 Focusing on reducing this risk by targeting obesity, rather than waiting for the clinical consequences to develop and then managing each independently is a well-established practice in preventative medicine.
Age-associated changes are responsible for most of the health problems of adult cats, and there are plausible hypotheses suggesting therapies that could directly target aging and so prevent these problems. The focus of geroscience (the study of the fundamental mechanisms of aging) is to identify these targets and therapies so the field of geriatrics (the clinical management of the aged) can move away from the reactive practice of treating the clinical consequences of aging as they arise and towards a preventative approach of delaying and preventing these consequences by modifying the fundamental processes of aging.
HOW DO CATS AGE?
The cellular and molecular processes associated with aging, and the tissue dysfunction and ultimate health problems that result from these processes, are complex and multifactorial. Research in laboratory species, and in humans and our feline companions, has elucidated many of these mechanisms, and our understanding of them is growing rapidly. Typical changes include diminished stem cell number and function, declining mitochondrial number and function, accumulation of aberrant and dysfunctional proteins, and many others.7
Despite the complexity of aging, it is ultimately just biology, a collection of physiologic processes that can be understood and manipulated like any other. There is a vibrant field of geroscience research investigating the processes of aging and potential targets for intervention to extend healthspan and lifespan.
Aging manifests in many visible physical changes, from greying and thinning of the coat to lenticular sclerosis and loss of lean body mass. Functional changes include decreased mobility and diminished hearing and vision. Behaviorally, old cats are often less active, less social, and more prone to anxiety and confusion, with many eventually developing cognitive dysfunction.5,8
WHEN IS A CAT “OLD”?
A single cutoff for senior or geriatric status is arbitrary and likely to misclassify many cats due to individual variation. Expert guidelines typically consider cats over 10 years of age to be seniors, and this is about the age with mortality appears to begin increasing, at least in some study populations.6,9,10
More important than chronological age, however, is biological age, defined as the degree to which aging has impacted the robustness, resilience, and state of health and function in an individual as measured by physical, functional, and biomarker assessment. We do not yet have reliable tools for measuring biological age, but many are being developed and tested, and ultimately this will be a much more accurate way to predict the age-associated risk of the three Ds (disability, disease, and death) in individual cats.
AGE-ASSOCIATED DISEASES AND CLINICAL PROBLEMS
Most categories of disease become more common in older cats, including neoplasia, degenerative musculoskeletal diseases (e.g. osteoarthritis and sarcopenia), chronic kidney disease, and others. Apart from congenital disorders, infections, and trauma, most of the significant diseases and causes of death cats experience result from the progressive accumulation of cellular and tissue changes associated with aging.6,8
Important clinical problems often develop which are not always associated with a specific diagnosis of disease. Loss of mobility, pain, sensory and cognitive decline, and many other such aging changes diminish quality of life, increase caregiver burden, and eventually lead to euthanasia. The common view of these as “natural” and inevitable part of the lifecycle impedes appropriate assessment and management of these conditions and delays necessary research to develop preventative interventions to extend healthspan.
A SYSTEMATIC APPROACH TO THE GERIATRIC FELINE PATIENT
Once age-associated health problems do develop, we can best care for our patients with systematic, rational, evidence-based assessment and management. This includes a regular repetition of the following cycle:
- Identify important disease and clinical problems
- Evaluate these problems using clinical assessment tools
- Develop an individualized management plan using available clinical practice guidelines and other scientific evidence
- Monitor the progression of the treated conditions and the impact of therapies using clinical assessment tools
- Adjust the plan based on follow-up assessment
ASSESSMENT AND MANAGEMENT TOOLS
An important part of a systematic approach to geriatric cats is consistent, objective assessment and management of age-related diseases and clinical problems. This is best accomplished with the regular use of validated clinical metrology instruments and reliance, when possible, on evidence-based clinical practice guidelines. There are many CMIs available or in development to quantify pain, quality of life, and the burden of care on the owners of geriatric cats.11–15 Repeated use of these allows detection of changes over time, better evaluation of the effectiveness of therapies than unaided observation, and better communication with owners to facilitate decision making.
There are also numerous clinical practice guidelines available to support management of the most common age-associated problems and diseases.10,16–19 While some are more rigorous and evidence-based than others, all offer rational and systematic approaches that can help clinicians make comprehensive treatment and management plans.
PITFALLS IN FELINE GERIATRICS
A systematic approach to geriatric medicine encourages proactive identification of disease and clinical problems and using the best available evidence to guide diagnostic and treatment interventions. Too often, clinical signs of frailty and disease are dismissed as “just slowing down” or “normal aging” rather than appropriately assessed, monitored, and managed. In the future, proactive and systematic detection of such signs will be a critical element in the determination of biological age and the decision to employ therapies targeting aging directly.
REFERENCES
1. Ukraintseva S, Yashin AI, Arbeev KG. Resilience Versus Robustness in Aging. Journals Gerontol Ser A. 2016;71(11):1533-1534. doi:10.1093/GERONA/GLW083
2. Miele A, Sordo L, Gunn-Moore DA. Feline Aging: Promoting Physiologic and Emotional Well-Being. Vet Clin North Am Small Anim Pract. 2020;50(4):719-748. doi:10.1016/J.CVSM.2020.03.004
3. McKenzie BA. Is Aging a Disease? DVM360. 2022;53(3):25.
4. Teng KT, Mcgreevy PD, Toribio JALML, Raubenheimer D, Kendall K, Dhand NK. Associations of body condition score with health conditions related to overweight and obesity in cats. J Small Anim Pract. Published online 2018. doi:10.1111/JSAP.12905
5. Miele A, Sordo L, Gunn-Moore DA. Feline Aging: Promoting Physiologic and Emotional Well-Being. Vet Clin North Am Small Anim Pract. 2020;50(4):719-748. doi:10.1016/J.CVSM.2020.03.004
6. O’Neill DG, Church DB, McGreevy PD, Thomson PC, Brodbelt DC. Longevity and mortality of cats attending primary care veterinary practices in England. J Feline Med Surg. 2015;17(2):125-133. doi:10.1177/1098612X14536176
7. McKenzie BA. Comparative veterinary geroscience: mechanism of molecular, cellular, and tissue aging in humans, laboratory animal models, and companion dogs and cats. Am J Vet Res. 2022;83(6). doi:10.2460/AJVR.22.02.0027
8. Bellows J, Center S, Daristotle L, et al. Evaluating aging in cats: How to determine what is healthy and what is disease. J Feline Med Surg. 2016;18(7):551-570. doi:10.1177/1098612X16649525
9. Quimby J, Gowland S, Carney HC, DePorter T, Plummer P, Westropp J. 2021 AAHA/AAFP Feline Life Stage Guidelines. J Feline Med Surg. 2021;23(3):211-233. doi:10.1177/1098612X21993657
10. Ray M, Carney HC, Boynton B, et al. 2021 AAFP Feline Senior Care Guidelines. J Feline Med Surg. 2021;23(7):613-638. doi:10.1177/1098612X211021538/ASSET/IMAGES/LARGE/10.1177_1098612X211021538-IMG1.JPEG
11. Buffington T. Development and Initial Validation of a Frailty Scale for Domestic cats.
12. Doit H, Dean RS, Duz M, Brennan ML. A systematic review of the quality of life assessment tools for cats in the published literature. Vet J. 2021;272:105658. doi:10.1016/J.TVJL.2021.105658
13. Reid J, Scott EM, Calvo G, Nolan AM. Definitive Glasgow acute pain scale for cats: validation and intervention level. Vet Rec. 2017;180(18):449-449. doi:10.1136/VR.104208
14. Klinck MP, Gruen ME, del Castillo JRE, et al. Development and preliminary validity and reliability of the montreal instrument for cat arthritis testing, for use by caretaker/owner, MI-CAT(C), via a randomised clinical trial. Appl Anim Behav Sci. 2018;200:96-105. doi:10.1016/J.APPLANIM.2017.11.013
15. Spitznagel MB, Jacobson DM, Cox MD, Carlson MD. Caregiver burden in owners of a sick companion animal: A cross-sectional observational study. Vet Rec. 2017;181(12). doi:10.1136/vr.104295
16. (IRIS) IRIS. Treatment Recommendations for CKD in Cats (2019) Treatment recommendations for Cats with Chronic Kidney Disease Stage 1 Feline patients. Published online 2019.
17. Epstein ME, Rodan I, Griffenhagen G, et al. 2015 AAHA/AAFP Pain Management Guidelines for Dogs and Cats. J Feline Med Surg. 2015;17(3):251-272. doi:10.1177/1098612X15572062
18. Sparkes A, Heiene R, Lascelles B, et al. ISFM and AAFP consensus guidelines: long-term use of NSAIDs in cats. J Feline Med Surg. 2010;12(7). doi:10.1016/J.JFMS.2010.05.004
19. Quimby J, Gowland S, Carney HC, DePorter T, Plummer P, Westropp J. 2021 AAHA/AAFP Feline Life Stage Guidelines: https://doi.org/101177/1098612X21993657. 2021;23(3):211-233. doi:10.1177/1098612X21993657
SUMMARY INCLUDING KEY “TAKE HOME” POINTS
- Aging is not an inevitable and immutable fact of life. It is a modifiable risk factor for the most causes of disability, disease, and death in adult cats.
- Numerous physical, function, behavioral, and metabolic changes occur in aging cats that lead to clinical disease, frailty, diminished quality of life, and a significant caregiver burden on owners.
- Aging is just biology! The cellular, molecular, and tissue changes that occur, and that lead to the feline aging phenotype, are complex but comprehensible. The better we understand these changes, the better we can intervene to mitigate them.
A systematic, evidence-based approach to assessment and management of diseases and clinical problems in geriatric cats, supported by validated clinical metrology instruments and clinical practice guidelines, is a more efficient, comprehensive, and effective strategy for high-quality patient care.
