Cognitive decline (aka dementia) is not considered a normal aging change, although its occurrence does increase with advanced age. Animals with decline in multiple cognitive aspects, in the absence of medical disease to explain this decline, are considered to have cognitive dysfunction syndrome (CDS).
 
Prevalence
Dogs – A study revealed that 28% of dogs aged 11-12 years and 68% of dogs aged 15-16 years showed one or more signs of cognitive impairment.
Cats – A similar study suggested that 28% of pet cats aged 11 to 14 years developed at least one sign consistent with cognitive dysfunction, and this increased to over 50 per cent for cats of 15 years of age or older.
 
Human correlations - Alzheimer’s disease
This disorder affects approximately 10% of people over 65 and 50% of people over 85. Degenerative changes may be found in multiple brain areas of affected patients. The primary disease process includes:
  • Amyloid plaques are an accumulation of β-amyloid (Aβ) as a result of the defective precursor proteins (APP).
  • Neurofibrillary tangles form from abnormal APP as well as from abnormal tau protein accumulation. Tau proteins are a normal part of cell transport mechanisms. In Alzheimer’s disease the abnormal tau proteins can lead to death of brain cells and a “tangle” of protein filaments.
Disease process in dogs and cats
Diffuse amyloid plaques are found in the front part of the brain of affected dogs around the age of 9 years. This is associated with memory and learning problems. The ability to voluntarily control elimination may also be affected, leading to housesoiling problems. With time the plaques progress to other brain structures which may lead to problems with spatial disorientation, wandering, and decreased vision and hearing capabilities.
Decreased neurotransmitter availability, perhaps due to increased enzymatic breakdown and increased free-radical may lead to decreased brain signally and cell damage. Neurofibrillary tangles have not been identified in the brains of CDS dogs and cats as they have been in humans.
 
Diagnosis
Your veterinarian will make a diagnosis of CDS in your pet based on the presence of 1 or more of the following "DISHA" signs which cannot be explained by a medical disease:
  • "D"isorientation – changes in spatial awareness, loss of ability to navigate around familiar obstacles, wandering behavior.
  • "I"nteraction changes – decreased interest in social interactions, petting, greetings, depended or “clingy” behaviors.
  • "S"leep/Wake cycle changes – restlessness or frequent waking during the night, increased sleep during daytime hours.
  • "H"ousesoiling – no longer lets owner know when it needs to go outside, indoor elimination, incontinence
  • "A"ctivity level changes – decreased exploration and response to things, people, sounds around the house, decreased grooming, decreased appetite; increased anxiety, including restlessness, agitation, and/or separation distress.
Diagnosis of exclusion
Medical causes for the above behavioral changes must be ruled out in order to make a definitive diagnosis of cognitive dysfunction syndrome.  Medical problems may include, but are not limited to: Cushing’s disease, parathyroid disorders, thyroid disorders, diabetes mellitus, chronic kidney disease, cancer, cardiovascular disease, incontinence, liver disease, musculoskeletal disease, dental disease, prostatic disease, and sensory loss.
Behavioral problems that look like CDS may include generalized anxiety, separation anxiety, fear-related aggression, pain-related aggression, noise or storm phobias, lack of housetraining, attention-seeking behaviors, and compulsive disorders. Often there will be concurrent behavioral and medical illness as medical and cognitive disorders may exacerbate existing, previously undiagnosed, behavior problems.
 
BEHAVIORAL SIGNS
SCORE
Score:  0=none,  1=mild,  2=moderate,  3= severe
 
DISHAA  
DISORIENTATION
Gets stuck, difficulty getting around objects, goes to hinge side of door  
Stares blankly at walls, floor, or into space  
Does not recognize familiar people/familiar pets  
Gets lost in home or yard  
Less reactive to visual (sights) or auditory (sounds) stimuli  
SOCIAL INTERACTIONS
More irritable/fearful/aggressive with visitors, family or other animals  
Decreased interest in approaching, greeting or affection/petting  
SLEEP/WAKE CYCLES
Pacing/restless/sleeps less/waking at night  
Vocalization at night  
HOUSESOILING, LEARNING AND MEMORY
Less able to learn new tasks or respond to previously learned commands/name/work  
Indoor soiling of urine 5 or stool 5/ decreased signaling to go out  
Difficulty getting dog's attention/increased distraction/decreased focus  
ACTIVITY
Decreased in exploration or play with toys, family members, other pets  
Increased activity including aimless or wandering  
Repetitive behaviors, e.g., circling 5 chewing 5 licking 5 star gazing 5  
ANXIETY
Increased anxiety when separated from owners  
More reactive/fearful to visual (sights) or auditory (sounds) stimuli  
Increased fear of places/ locations (e.g., new environments/going outdoors)  
TOTAL  
4-15 consistent with mild CDS; 16-33 consistent with moderate CDS; >33 consistent with severe CDS
Assessment created by Dr. Gary Landsberg, DV, DACVB, DECAWBM
 
 
Treatment
There is no cure for cognitive dysfunction and the disease is progressive; however, therapies in the form of environmental enrichment, dietary change, supplements, and psychoactive drugs have been shown to delay progression and improve the associated behavioral signs. Any therapy found to be effective should be continued for life as long as there are no problems (liver or kidney disease, drug interactions, dietary intolerance, etc.)
  • Environmental Enrichment in the form of exercise, new and interactive toys, and learning new tasks – “teach an old dog new tricks” – has been shown to improve learning and memory.
  • Diet change –Vitamins E and C, the antioxidants beta carotene, selenium, alpha-lipoic acid, flavonoids and carotenoids from fruits and vegetables, L-carnitine to enhance mitochondrial function, and omega-3 fatty acids to promote cell membrane health. In clinical trials this diet alone significantly improved learning in dogs with CDS. When combined with environmental enrichment these results were even greater.
  • Dietary Supplements are now available for both dogs and cats: SenilifeTM, ProneurozoneTM, Denosyl®/Denamarin® (SAMe) are a few examples of those available for dogs and cats in the US. Your veterinarian will be able to recommend the appropriate supplement if one is right for your pet.
  • Psychoactive drugs: Anipryl® (selegiline) is the only drug approved for use in dogs with CDS.

Prognosis

  • 48% of dogs 11-14 years old showing signs of impairment in one behavioral category develop impairment in two or more categories within 6-18 months without treatment.
  • Clinical trials have shown improvement in existing behavioral signs of CDS and delay of onset of additional signs in several of the treatment modalities discussed here.
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