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Uncle Terry_1

Photo by Dr. Lisa Wilhelm

At age 19, Uncle Terry had a variety of health issues, but they didn't explain why he suddenly started yowling at all hours.

Dr. Lisa Wilhelm was at her wits' end with Uncle Terry. Her 19-year-old cat had developed a habit of screaming, night and day, without a clear reason. Wilhelm found carrying on phone calls impossible, and, unless he was sent to the basement at bedtime, Uncle Terry's loud meows kept the household awake.

The cat was a bit hard of hearing, arthritic and had irritable bowel syndrome. But with unremarkable blood work and normal blood pressure, the cat's new vocalizations seemed unrelated to his preexisting conditions.

Ultimately, Wilhelm determined that Uncle Terry likely had dementia, a disease that is notoriously difficult to diagnose in senior cats and dogs. But research is progressing, and experts are encouraging veterinary practitioners and pet owners alike to learn how to spot it.

Known officially as cognitive dysfunction syndrome (CDS), canine and feline dementia is an age-related neurodegenerative condition that manifests as mild to severe behavioral changes. Like in humans with Alzheimer's disease, proteins gradually build up in the dogs' and cats' brain tissue, causing atrophy and damaging cognition. Veterinarians diagnose pets with CDS by having caretakers closely monitor the dog or cat using behavior questionnaires. The disease is incurable, but treatment can help improve affected pets' quality of life and slow their disease progression.

CDS isn't technically considered fatal. Unlike Alzheimer's disease, it's not known to directly cause organ failure. Dogs and cats with CDS are usually euthanized only when they clearly display a poor quality of life or have another condition that is terminal.

According to veterinary researchers, the disease is tough to study; pets regularly go undiagnosed, and while MRIs can show some loss of brain matter, thorough brain examinations of animals with confirmed cases can be done only postmortem. But researchers are working to improve the veterinary community's awareness of CDS and uncover just how similar dementia in dogs, cats and humans — and its treatment — may be.

Recalling the early days of Uncle Terry's cognitive decline, Wilhelm, a small animal relief veterinarian based in Iowa, said, "It really was an insidious onset. We first just started to feel like Uncle Terry was old and not paying as much attention to his surroundings as he used to. But then he started staring at walls or off in the distance, caterwauling."

As Wilhelm experienced, clinical signs in the early stage of CDS are subtle: The pet may sleep less at night, cling more to its owner and become less active — changes that caretakers and veterinarians often attribute to typical aging. Moderate or severe behavior changes — like Uncle Terry's hollers — are more noticeable, but their cause can still be challenging to pinpoint, since other medical conditions must be ruled out first. Pets may start having anxiety attacks; vocalize more, unprovoked; and have toileting accidents despite being house-trained.

To help veterinarians and caretakers assess brain health, Dr. Gary Landsberg, a veterinary behaviorist based in Ontario, Canada, and a longtime CDS researcher, published a behavior change checklist in a book he coauthored in 2003. As research progressed, Landsberg and other experts refined the checklist for dogs. Today, it is known as DISHAA, which stands for disorientation, impaired interactions, sleep-wake cycle, house soiling, activity changes and anxiety. (Some versions of the checklist include learning and memory changes and go by the acronym DISHAAL.) The checklist is in the form of a questionnaire designed to evaluate a dog's cognitive decline based on behavior changes. Users assign a score from zero (no signs of change) to three (severe signs of change) to each category and total the scores to determine if CDS is present and how far it's progressed.

(There is no validated feline-specific CDS scale. Researchers in the United Kingdom, however, have proposed a modified acronym, VISHDAAL, for identifying behaviors seen in cats with CDS. It slightly reorders the behaviors in the canine list and adds extreme vocalizations to the top.)

Ideally, owners should complete a questionnaire annually once their pet turns 7 years old and twice a year after age 10, Landsberg said. But the survey has historically flown under the radar in general veterinary practice, much like some CDS research itself.

'It wasn't seen as a real condition'

The first studies on canine CDS began popping up in the early 1990s, many exploring how senior dog brains could serve as models for studying the pathology of dementia in humans. The first drug for CDS — the medication L-deprenyl (now called selegiline) — was approved in 1999. Two years later, Hill's Pet Nutrition released a therapeutic "brain aging care" diet.

Research on feline CDS surfaced in the early 2000s, but it took much longer to catch the scientific and veterinary practitioner community's attention than its canine equivalent, Landsberg said.

"Back in 2003, Dr. Kelly Moffat, my resident at the time and now a veterinary behaviorist, and I did a prevalence survey in about 150 senior cats, finding that about 25% of them overall showed signs of CDS," he recalled. "We submitted it for publication, but it was rejected because ‘No one [had] established cognitive dysfunction as a true condition in cats.' It was like the chicken and the egg. Our study could've helped to establish it as a real condition, but we couldn't publish it because it wasn't seen as a real condition."

Feline CDS is now understood as a real condition. It affects an estimated 25% of cats 11 to 14 years old and 50% of cats 15 and older, according to Moffat's and Landsberg's unpublished 2003 abstract, which appeared in the proceedings of two veterinary conferences where their findings were presented. The study has since been cited regularly in other peer-reviewed, published CDS research.

But the disease is still frequently overlooked in general practice, likely because changes in cat behavior can be extra tricky to detect, Landsberg said. Cats can be more aloof and seemingly less dependent on their owners than dogs. They might graze on food throughout the day and come and go from a house as they please. Beneath the surface, a lot can be happening.

A study published in August 2025 that examined the brains of 25 cats postmortem found that all of those age 8 and older (18 of the 25) had amyloid-beta plaques — toxic clumps of protein — glommed on the synapses, the critical junctions where brain cells communicate. Eight of the 18 cats that had been suspected to have CDS based on their behavior had notably more inflammation and brain tissue loss around the plaques than in areas without plaques.

in the aged cats there was more inflammation and brain tissue loss around the plaques than in areas without plaques

Humans with Alzheimer's disease and dogs with CDS exhibit the same neuroinflammation and deterioration caused by amyloid-beta plaques, suggesting that dementia pathology in the three species is remarkably similar.

Alzheimer's research is largely done using laboratory mice that are genetically modified to develop amyloid-beta plaques and other brain gunk, such as tau protein clusters, which form in the neurons of people with Alzheimer's. The disease has been cured in mice, but they aren't ideal models; their lifespans are much shorter than humans'. Cats and dogs are more promising models.

Millie

Photo courtesy of Dr. Sarah Gottschalk

A diagnosis of cognitive dysfunction syndrome in Millie, 14, enabled her veterinarian owner to determine how best to treat Millie's growing anxiety and disorientation.

"The disease in humans occurs slowly over many decades as we age," explained Dr. Robert McGeachan, a veterinary neurology and neurosurgery resident at the University of Edinburgh and lead author of the cat study, which was published in the European Journal of Neuroscience. "It's not nearly as sudden or severe as the way it's coded in lab mice. ... But cats and dogs gradually develop the disease naturally over many years, roughly progressing at the same pace relative to the human lifespan. So they could be a much more translatable model of disease."

Identifying, studying and treating CDS in pets while they're still with us is also a major goal, of course. That's why 12 veterinarians, including Landsberg, came together in January 2025 to form the Canine Cognitive Dysfunction Syndrome Working Group. The team subsequently published a paper (published online in December and in-print in April) in the Journal of the American Veterinary Medical Association that outlines the disease definition, severity stages (as assessed with DISHAA) and diagnostic levels. Canine CDS information and resources are available on the working group's new website hosted by the American Kennel Club Canine Health Foundation.

"We expect with age that a dog's cognitive function will decline, so determining what's 'normal' aging and what's an early sign of CDS is hard," said Dr. Natasha Olby, lead author of the working group's paper and a professor of veterinary neurology at North Carolina State University College of Veterinary Medicine. Since the 1980s, when Alzheimer's research gained momentum, experts have learned to differentiate that disease from other forms of dementia and cognitive impairment in people and to improve disease guidelines, she added. "It was time for us, like them, to pull all of [the research] together to try and help veterinarians learn how to better approach [CDS]."

Two experts at Colorado State University — one in veterinary medicine and the other in human medicine — also have teamed up to tackle canine CDS and Alzheimer's disease by helping to lead the Brain Health Study, a nationwide longitudinal project that involves more than 500 canine participants of various ages and breeds. The researchers, Dr. Stephanie McGrath (a veterinary neurologist) and Julie Moreno (a neurotoxicologist), are tracking the dogs' cognitive and physical health through routine owner questionnaires, blood work, MRIs, spinal taps and brain health tests, such as treat-finding puzzles.

The study is part of the larger Dog Aging Project, which began in 2014 and was recently featured on a segment of the CBS newsmagazine 60 Minutes.

The researchers stated in a recent episode of CSU's The Next 150 podcast that, among other long-term research goals, they hope the work will help them catch early signs of CDS in their participants so that owners can act fast to implement treatments.

Slowing the progression

While not typically considered fatal, the disease is degenerative, and treatment of its clinical signs with medications, diets and/or enrichment activities can help slow its advance.

For Dr. Sarah Gottschalk, a CDS diagnosis in her own 14-year-old Pekingese, Millie, helped her determine the best medications and dosages to treat Millie's growing anxiety and disorientation.

"I've done [the DISHAA questionnaire] twice now since last year, when we suspected she might have [CDS], and she's progressed from mild to moderate," said Gottschalk, an urgent care veterinarian in upstate New York. "It's certainly been a process of ups and downs and fiddling with medications, but she's currently in a very good place and is managing her symptoms well just with Zoloft."

Grace

Photo courtesy of Dr. Gary Landsberg

Grace was 12 when she was diagnosed with CDS. Given a special diet and medication, she lived to be 16.

The medication selegiline is the only drug approved by the U.S. Food and Drug Administration to treat CDS in dogs. Veterinarians sometimes prescribe it off-label in cats with CDS, since there have been reports of benefits in clinical cases. It contains monoamine oxidase (MAO) inhibitors, which help improve communication between neurons in the brain by blocking harmful proteins. Other drugs, including Zoloft (sertraline), Prozac (fluoxetine) and gabapentin, can also help treat anxiety in pets with and without CDS.

Millie is an extremely picky eater and isn't motivated by food, Gottschalk said. But for dogs and cats with broader palates, CDS-specific diets, which typically include foods high in antioxidants, fatty acids and vitamin B, have proven helpful for treating clinical signs. Treat puzzles, such as snuffle mats, and other enticements to play can also be useful to stimulate healthy brain activity.

"There's enough evidence to show that social and physical enrichment and a good predictable environment are very, very helpful, both in regards to prevention of the onset of CDS and in treatment," Landsberg said.

Like Wilhelm and Gottschalk, Landsberg has cared for a pet of his own with CDS. He diagnosed his Nova Scotia duck tolling retriever, Grace, in 1997. Age 12 at the time, she'd begun regularly whining, staring off into space and responding less to verbal cues. Grace was put on the Hill's diet for canine CDS and selegiline and lived to be 16.

"She was my go-to case study back then," Landsberg said. "I called the lecture 'Growing Old Gracefully.' "

Correction: This story has been changed to correct the description of McGeachan's field of expertise. It also has been changed to clarify McGeachan's study findings about brain tissue loss in cats and about the disease development period in humans.