Aging Gracefully With Cognitive Dysfunction Syndrome

Dogs and cats are more than pets—they are family members. They share homes, secrets, and countless life experiences with their family, creating strong human–animal bonds. With modern veterinary care, pet lifespans have increased.¹ These additional years bring joy, but health challenges are common. Along with the body, the brain ages, and its optimal functioning declines with time. This can negatively impact a pet’s behavior, daily activities, social interactions, and quality of life.² Veterinary nurses can help educate clients about their pet’s aging brain and guide prevention and management strategies and prescribed treatment plans.

Cognitive Dysfunction Syndrome Overview

Sensory information processing, behavioral responses, learning, and memory formation are all part of cognition.³ Cognitive dysfunction syndrome (CDS) describes the degenerative anatomic and physiologic brain changes and cognitive and behavioral signs that occur during aging. CDS is a progressive disease that affects dogs and cats and is often compared to Alzheimer disease in humans.³ For decades, dogs have been used to study causes of and treatments for Alzheimer disease, as they display similar brain and behavior changes. Cats have recently been added as effective models.

In dogs and cats with CDS, brain imaging reveals signs such as decreased brain volume, loss of neurons and synapses, accumulation of amyloid β plaque, changes in blood flow such as microhemorrhage, and oxidative DNA damage. These structural changes reduce the effective transmission of neurochemicals necessary for nervous system communication.⁴

Clinical Signs

Categories of clinical signs of CDS in dogs and cats are listed in TABLE 1. The mnemonic acronym DISHAA is used to represent these categories in dogs, and VISHDAAL has recently been introduced for cats. Not all pets with CDS display signs in every category.

Other medical or behavioral problems can present with similar signs (see Signs of Aging in Senior Pets sidebar). For example, house soiling can occur with urinary tract infections, diabetes mellitus, and pain-related conditions such as osteoarthritis as well as with CDS. Changes in activity level or anxiety could be due to behavioral problems such as thunderstorm or noise phobias or generalized anxiety. CDS can also escalate or alter existing behavior problems, and treatment may need to address both issues. 

Causes

The cause of CDS is unknown, but advancing age is the biggest predictor of occurrence.⁶ Aging, also called senescence, decreases the body’s ability to adapt to physiologic, immunologic, and environmental stressors, resulting in low-grade inflammation.⁷ These age-related inflammatory changes are known as inflammaging.⁸ Immune dysfunction occurring with age is also known as immunosenescence.⁹ When the immune system is dysfunctional and inflammation is chronic, the brain undergoes chemical and anatomic changes that result in cognitive decline and CDS.

The formation of amyloid β (senile plaques) and tau protein plaques in the brain has long been associated with Alzheimer disease and has also been found in dogs with CDS.^10,11 These plaques impair neuronal functions and further neurodegeneration. When neurons cannot communicate effectively, cognitive changes occur.¹⁰

Research into the potential role of the gut microbiome has been advancing rapidly. The gut and brain communicate bidirectionally through the gut–brain axis (central nervous, endocrine, and immune systems).¹² The microorganisms in the gut play a significant role in neuron development, neurotransmitter production, and thereby cognition.¹³ Microbiome imbalance or dysbiosis has been found in patients with Alzheimer disease, and it is postulated the disease may begin in the gut.¹⁴ Aging, stress, chronic inflammation, invading pathogens, antibiotics, diet, and environmental toxins can affect the microbiome. 

Diagnosis

Evaluating behavior is key to diagnosing CDS, and several surveys have been designed as measurement tools. For dogs, the CADES (Canine Dementia Scale), the CCDR (Canine Cognitive Dysfunction Rating) scale, and the CCAS (Canine Cognitive Assessment Scale) are available.^15-17 A scale specific for cats was developed by MacQuiddy et al.¹⁸ These questionnaires rely on the client’s observation of their pet at home; therefore, their accuracy may be skewed by the client’s under- or over-reporting behavior occurrence and severity. Research centers have used task-based learning and memory tests for dogs and cats to study cognition and CDS. A validated at-home version of these tests to enhance diagnostic methods is not yet available.

Magnetic resonance imaging can reveal CDS-related anatomic changes in the brain, including amyloid β plaques, but absence or severity of such changes does not always correlate with cognitive signs. Recent research has revealed certain blood biochemistry markers associated with CDS, specifically alanine aminotransferase, aspartate aminotransferase, sodium, chloride, and the central nervous system injury biomarker NfL (neurofilament light).¹⁹ However, in-clinic testing protocols and parameters specific to CDS diagnosis are not yet established.

Without a definitive cause and because signs overlap with various age-related diseases, a diagnosis of CDS is based on exclusion.²⁰ A comprehensive assessment should include a thorough medical examination that evaluates all body systems. For example, the musculoskeletal system should be evaluated for pain or movement limitations that could impact the pet’s activity level or elimination choices, and a neurologic examination could help rule out altered mentation, proprioception, or other deficits that could alter behavior. Sensory organs can be checked to determine if decline that could impair perception and social interaction is occurring.

Blood analysis can be used to determine overall organ health and reveal endocrine pathologies such as hypothyroidism or hyperthyroidism, which can affect behavior. When elimination behavior changes are observed, a urinalysis can help assess kidney and bladder health and a fecal analysis can rule out parasitic involvement. Hypertension can also influence behavior; therefore, a blood pressure check can be helpful. Additional diagnostics or referral to a specialty service might be indicated based on general examination and laboratory test and behavior history findings.

A behavior history and CDS-specific owner questionnaire should inquire about the pet’s daily routine, family members, and lifestyle. The frequency and intensity of any behavior concerns, their initial occurrence, and how they may have changed over time with correlation to household events should be determined.

Prognosis

CDS is a progressive disease without a known cure. As the pet ages, more signs of cognitive decline are likely. Increased awareness of observable signs, prevention of contributing factors when possible, early treatment, and client support can combine to enhance the pet’s quality of life. 

Management and Treatment of Cognitive Dysfunction Syndrome

Although CDS cannot be cured, only managed, it is best treated with a comprehensive care plan that addresses the brain, body, and behavior. Dietary adjustments, supplements, medications, and physical and mental exercise should all be considered.

Diet

Senior pets have different nutritional needs than younger animals, such as fewer calories to match their activity level, higher protein to retain muscle mass, and increased digestibility to ensure effective nutrient absorption. Pets with CDS can benefit from dietary ingredients that focus on aging and brain changes.

Omega-3 fatty acids (docosahexaenoic acid and eicosapentaenoic acid) have been shown to decrease inflammation, antioxidants (vitamins C, E, and B) fight free radical damage in the brain, and medium-chain triglycerides provide an effective brain energy source.²¹ Many pet food manufacturers have added these nutrients to senior diets. Two therapeutic canine veterinary diets specially formulated for brain health are Hill’s Prescription Diet b/d Brain Aging Care (hillspet.com) and Purina Pro Plan Veterinary Diets NC NeuroCare (proplanvetdirect.com).

Microbiome modulation is being explored for humans with Alzheimer disease, but definitive treatment recommendations for humans, dogs, or cats are premature.²² Therapies in consideration are antibiotics to decrease pathologic bacteria; prebiotics, probiotics, and postbiotics to boost beneficial organisms; fecal microbiota transplantation to reboot the microbiome; and other emerging biotechnologies.²³

Supplements

Several dietary supplements are available for pets with CDS and are intended to benefit general health or help relieve signs of CDS (BOX 1). These supplements are given daily and may take several weeks for full benefits to be observed. Some labeled for dogs have been used off-label in cats.

Medications

Despite decades of research and multiple drug developments, effective prevention or removal of amyloid β and tau protein plaques in animals and humans has remained elusive.

Selegiline (Anipryl; Zoetis, zoetisus.com), a monoamine oxidase inhibitor, is the only drug labeled for CDS in dogs. It inhibits the destruction of the neurotransmitter dopamine, decreases free radical damage, and increases nerve growth factor. When started early, it can improve clinical signs.²⁴ Selegiline has been used off-label in cats with anecdotal success.

Common behavior medications such as fluoxetine, clomipramine, and amitriptyline all increase the neurotransmitter serotonin, as do amitraz (a tick and mite killer) and mirtazapine (an antinausea drug/appetite stimulant). Excessive serotonin levels can cause serotonin syndrome with signs that can include elevated heart rate, difficulty breathing, dilated pupils, tremors, increased temperature, and high blood pressure. Phenylpropanolamine, a medication often used for urinary incontinence, can also cause high blood pressure if combined with selegiline.

Because effective medications to prevent or cure CDS do not yet exist, the following medications are often used off-label to manage clinical signs in dogs and cats:

• Human antidepressants/antianxiety medications (e.g., fluoxetine, sertraline, buspirone, bupropion) given daily can help reduce signs of irritability, restlessness, repetitive behavior, and anxiety in dogs and cats. Reconcile (fluoxetine hydrochloride; PRN Pharmacal, prnpharmacal.com) and Clomicalm (clomipramine hydrochloride; Virbac, us.virbac.com) are veterinary drugs labeled for separation anxiety in dogs and may be used for signs of CDS.
• Sedatives and other anxiety-reducing medications (e.g., gabapentin, trazodone, benzodiazepines) can be used as needed to help with restlessness, sleep disturbance, pacing, and anxiety.
• Propentofylline (Vivitonin, MSD Animal Health; currently unavailable in the United States) can decrease free radicals and inflammation in the brain and improve the synthesis of nerve growth factors.
• Nicergoline (Fitergol, Merial; currently unavailable in the United States) can improve blood circulation within the brain.

Many board-certified veterinary behaviorists (dacvb.org) offer professional consultations with general practitioners to discuss cases and medication options.

Enrichment and Exercise

Stimulating a pet’s sensory systems and physical exercise can benefit brain health.²⁵ Clients should be encouraged to offer enrichment for each sense organ and provide variety (BOX 2). 

Food-based enrichment may create the most dramatic interaction, but other sensory experiences, even if the engagement is brief, are still valuable (FIGURE 1).

Figure 1. Food-based enrichment in the form of a food puzzle. Courtesy Paisley Lunchick

For dogs, going for a walk stimulates all senses and can be very enriching. If the dog’s mobility is limited, the client can capture “scent pictures” and bring the enrichment to them. Collecting a scent picture requires only a rag and a plastic bag; the client can rub the rag on an object or area to transfer the scent, then seal it in the bag to take home, where they can take it out and present it to the pet for sniffing (FIGURE 2). If the client has an able-bodied dog, that dog can help determine the best scents to collect during walks.

Figure 2. “Scent picture.” Senior dog with limited mobility sniffing interesting scents collected during their caregiver’s daily walk.

Another form of practical enrichment is playing training games with the pet. Clients can either practice the pet’s favorite tricks or teach them new ones using positive reinforcement training. Pets with mild cognitive decline can still learn. Training is cognitively enriching, provides social bonding, and can teach functional life skills such as how to walk up a ramp.

Complementary Therapies

Products that can have a general calming effect may help pets with CDS. Species-specific pheromones for dogs (Adaptil, Ceva [ceva.com]; Thunderease, ThunderWorks [thundershirt.com]) and cats (Feliway; Ceva, us.feliway.com), body wraps that apply gentle swaddling-like pressure (Thundershirt; ThunderWorks, thundershirt.com), and essential oils such as lavender and chamomile can be tried. Alternative veterinary modalities such as acupuncture and massage may also be indicated.

Environmental Adaptations

Modifying the home environment to meet the aging pet’s comfort and functionality is often necessary. Pets with CDS are more easily stressed, which can negatively affect overall health and hasten cognitive decline. Enabling the pet to remain active and engage in their favorite activities boosts wellbeing. Clients should focus on the pet’s daily core needs and adjust to match their preferences and the household’s unique environment. Veterinary nurses can recommend options that allow choice, making changes gradually, being patient if the pet’s adjustment is slow, and maintaining consistent and predictable schedules. The following are some common, useful adaptations:

• Eating: Use raised bowls that do not easily slide or tip, warm food to enhance smell and taste, and a preferred food texture and size that can be easily chewed.
• Drinking: Use raised bowls that do not easily slide or tip and provide the pet’s preferred water temperature and bowl type. Some pets prefer a water glass with ice cubes, shallow dishes, a dripping faucet, or pet water fountains with filtered water.
• Resting/sleeping: Provide pet stairs or ramps to allow the pet to get onto the bed or couch; warming devices; bed padding and covers that do not tangle, trip, or limit balance; easily washable pet beds; quiet, undisturbed space that is safe from being stepped on or bumped; and natural daylight and darkness for proper circadian rhythm.
• Mobility: Provide nonslip rugs to ensure traction and prevent falls, extra space to navigate furniture and obstacles to minimize tight turns and backing up, harnesses and support slings for balance and lifting, ramps as an alternative for stairs, and ramps or steps to get pets in and out of vehicles.
• Social interaction: Give plenty of attention, petting, play, and preferred activities for bonding. Provide abundant and accessible basic resources to prevent competition between household pets.
• Hygiene: Perform gentle bathing and grooming using techniques the pet prefers.
• Elimination: Provide extra litter boxes with low sides, easy access to toileting areas/litter boxes, extra walks or toileting trips with rewards for going, waterproof beds, and furniture covers.

Summary

Pet dogs and cats are living well into their senior years, and preparing for and supporting their changing medical and behavioral needs are key. CDS can be a challenging condition to navigate and can greatly affect quality of life. Veterinary nurses educated in cognitive care can advocate for patients’ needs and support clients to maximize a long, healthy relationship.