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Cognitive Dysfunction Syndrome (CDS)

Over the last 40 years, the lives of pets have evolved towards safer, more sedentary and controlled lifestyles. Their living standards have increased and with the advances in modern veterinarian medicine and most deadly infectious diseases under control, domestic dogs and cats often live long enough to develop cognitive dysfunction, obesity and arthritis. (2, 3, 5)

With old age, pets can develop cognitive impairments, just like humans. Cognitive dysfunction syndrome (CDS) is a degenerative brain disease in pets equivalent to Alzheimer’s diseases in humans.



Cognitive dysfunction syndrome – Alzheimer’s disease for pets

“Although dementia is almost never fatal on its own, CDS and physical health problems are a debilitating combination,” explains the veterinarian Lee Haris. (1, 5)The symptoms of the disease are comparable in humans and pets and can be grouped under the acronym DISH


- Disorientation - seem confused, pace and wonder aimlessly, trouble finding the door, walking in circles, staring at walls

- Interaction changes - erratic behaviour, begging for food when their bowl is full, loss of interest in family members

- Sleep changes - sleep more and up at all hours of the night,

- house soiling and forgetfulness – forget old tricks and training


CDS has only been recently recognised as a disease in pets. It is surprisingly common but often goes unnoticed, with only 2% of the sick dogs diagnosed. (4) The symptoms often go unseen or classified under the “ageing” process. It is “usually a diagnosis by exclusion. If anything else is checking out normally, it’s probably CDS” says Jennifer Bolster, chief clinician at the humane Society of Boulder Valley Colorado. (2) Over 50% of dogs and cats are estimated to exhibit symptoms of the disease during their lifetime which might cause your animals to become confused and aggressive for no apparent reason. The condition worsens with age so that a quarter of cats between 11 and 14 and 62% of dogs aged 11 to 16 demonstrate one or more signs of CDS. (2, 4, 9, 10)


Degeneration of the brain

With old age, the brain becomes smaller mostly due to the loss of the connections – dendrites and axons – between nerve cells. In dogs this change is quite significant, older brains can be up to 25% lighter. Age brings along physical but also chemical changes, some of which can affect behaviour, memory and learning. In dogs and humans, mitochondria - the power source of a cell – become less efficient with age and start leaking out ‘free radicals’, chemicals that oxidize compounds essential for normal cell function. The loss of these compounds places the cells at risk, and synapses are lost.

Unlike other organs, the brain cannot repair itself from oxidative damage. With age in dogs and humans, as the tissues degenerate, toxic protein deposits called “amyloids” naturally accumulate in the brain, resulting in brain cell dysfunction. The starch like protein builds up, becomes waxy and forms plaques that gradually clog the brain and inhibit the transmission of signals in the brain.

Physical evidence found during autopsies has revealed the same sort of degenerative brain lesions in dogs and humans. (12) “Really our brains are not that different from dogs”, says Lee Haris. “The cellular changes of canine cognitive dysfunction would be recognizable under the microscope to any human pathologist: plaques of beta amyloid – protein fragments believed to be the result of oxidative stress.” (1)

Researchers at the University of Toronto have shown that dogs with high levels of amyloid plaques in the brain have poorer memory and difficulties learning new material, just like in CDS. (8) Levels of amyloid plaques, especially associated with clusters of dead or dying cells, predict the severity of the mental or cognitive impairment and are evidence that an individual is suffering from Alzheimer’s disease or CDS. (6)

Neurotransmitters in the brain are also altered in CDS, which often leads to abnormal behaviour. Dogs with CDS have the same depletion of the chemical dopamine that occurs in humans with Alzheimer’s. (7)


Fighting the debilitating disease

There isn’t a cure for CDS but there are ways to manage the disease and help pets live better. Early diagnosis and intervention can slow the mental decline of this progressive disease.  Treatment of CDS and Alzheimer’s alike is most effective before the symptoms start to show, which is why researchers are working on tests to predict Alzheimer’s long before symptoms appear, tests which will hopefully be transferrable to CDS. In 2013, the FDA approved the second compound to help confirm Alzheimer’s in humans. (7)

It is important to keep a pet “brain active” – enriching the environment, teaching it tricks, going outside so the brain doesn’t deteriorate as quickly. Maintaining good mental function as long as possible delays the onset and progression of cognitive decline. (14, 15)

It is also important to keep pets nutritionally balanced. Antioxidants in a pet’s diet protect the brain from free radical damage and omega-3 essential fats are crucial for cognitive health. Prescription diets fortified with antioxidants, fatty acids and L-carnitine are freely available. (12)

A healthy diet, mental stimulation, human contact and physical exercise can help prevent cognitive decline in pets as in humans but there are also drugs available to stall the progression of the disease. There is an FDA- approved medication to treat CDS: Selegine, a MAO (Monoamine oxidase) inhibitor antidepressant in people sometimes used   for human Alzheimer’s and Parkinson’s patients. It prolongs the activity of your pet’s remaining dopamine and enhances the amount of chemicals within the brain that act as messengers between nerve cells. Other drugs can also be used to treat age-related behavioural disorders by enhancing blood circulation to the brain or increase brain activity. (7)

Physical and behavioural changes are similar in both Alzheimer’s and CDS. So similar, we can borrow from the extensive research that has been done in humans and lab animals to help understand what will delay the onset of senile dementia in pets. (5) Conversely, dogs are also increasingly being used as models to study the disease in humans. (11, 12, 13)


  8.  Studzinski CM, Christie LA, Araujo JA, Burnham WM, Head E, Cotman CW, Milgram NW Neurobiol Learn Mem. 2006 Visuospatial function in the beagle dog: An early marker of cognitive decline in a model of human aging and dementia.Neurobiol Learn Mem. 2006 Sep;86(2):197-204.
  9.  Vet J. 2011 Jun;188(3):331-6. doi: 10.1016/j.tvjl.2010.05.014. Epub 2010 Jun 12. The canine cognitive dysfunction rating scale (CCDR): a data-driven and ecologically relevant assessment tool. Salvin HE1, McGreevy PDSachdev PSValenzuela MJ.
  10.   Top Companion Anim Med. 2011 Feb;26(1):17-24. doi: 10.1053/j.tcam.2011.01.005. Cognitive dysfunction in cats: clinical assessment and management. Gunn-Moore DA1.
  11.  Studzinski, CM, Araujo, J and Milgram, NW. The Canine Model of Human Cognitive Aging and Dementia: Pharmacological Validity of the Model for Assessment of Human Cognitive-Enhancing. Progress in Neuropsychopharmacol. and Biol. Psychiat. 2005, 29:489-498; Review.
  12.  Opii WO, Joshi G, Head E, Milgram NW, Muggenburg BA, Klein JB, Pierce WM, Cotman CW, Butterfield DA. Proteomic identification of brain proteins in the canine model of human aging following a long-term treatment with antioxidants and a program of behavioral enrichment: relevance to Alzheimer's disease. Neurobiol Aging. 2008 Jan;29(1):51-70. Epub 2006 Oct 20.
  13.  Studzinski CM, Christie LA, Araujo JA, Burnham WM, Head E, Cotman CW, Milgram NW Neurobiol Learn Mem. 2006 Visuospatial function in the beagle dog: An early marker of cognitive decline in a model of human aging and dementia.Neurobiol Learn Mem. 2006 Sep;86(2):197-204.
  14.  Milgram NW, Siwak-Tapp CT, Araujo J, Head E. Neuroprotective effects of cognitive enrichment. Ageing Res Rev. 2006 Aug; 5(3):354-69.
  15.  Siwak-Tapp CT, Head E, Muggenburg BA, Milgram NW, Cotman CW. Region specific neuron loss in the aged canine hippocampus is reduced by enrichment. Neurobiol Aging. 2008 Jan;29(1):39-50. Epub 2006 Nov 7.

Last edited: 23 June 2015 11:50

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