To diagnose the cause of behavioral signs in a geriatric dog, a detailed history, physical examination, neurologic evaluation, and diagnostic tests are required to exclude potential medical causes of the presenting signs. Many owners do not report these signs, perhaps because the owners think they are insignificant or assume little can be done. Yet in one study, 30% of dogs 11–12 yr old and nearly 70% of dogs 15–16 yr old had signs consistent with cognitive dysfunction syndrome (CDS). A more recent Internet survey estimated CDS in 14.2% of dogs >10 yr old, with prevalence increasing with age, but >85% of these had not been diagnosed. It is therefore essential that owners be informed of the importance of reporting signs when they arise and for veterinarians to take a proactive approach in asking owners about behavior at each visit. Early detection provides the best opportunity to improve signs and slow the decline of cognitive function.
Aging dogs may exhibit a decline in cognitive function (memory, learning, perception, awareness) that manifests as one or more of a group of clinical signs. These are sometimes referred to by the acronym DISHA and include disorientation, interactions, sleep-wake cycles, housesoiling, and activity changes (which may be decreased or increased and repetitive). In addition, anxiety, agitation, and altered responses to stimuli are frequently reported. The first and most prominent sign of brain aging is a decline in learning or memory, which is generally impractical for pet owners to assess. However, neuropsychologic testing of older dogs has documented memory decline beginning at 6–8 yr of age and learning deficits by 9 yr of age. CDS in dogs is analogous to the early stages of Alzheimer disease in people, both in clinical signs and brain pathology. As with people, some dogs show minimal to no clinical impairment with age, whereas others develop varying degrees of deficits.
Treatment should first focus on environmental enrichment (both physical and mental stimulation), which has been shown to slow cognitive decline and improve the signs of CDS. Selegiline is a monoamine oxidase B inhibitor that may improve the signs of CDS by enhancing dopamine and other catecholamines in the cortex and hippocampus and by decreasing free radical load. Propentofylline, which is licensed in Europe and Australia for the treatment of dullness, lethargy, and depressed demeanor in old dogs, may increase blood flow and inhibit platelet aggregation and thrombus formation.
A number of natural products, including diets and supplements, have also been shown to have beneficial effects in improving the signs and potentially slowing cognitive decline. Two such diets are Canine b/d®, which is supplemented with fatty acids, antioxidants, and dl-alpha-lipoic acid and l-carnitine to enhance mitochondrial function, and a specialized Purina One® diet that uses botanic oils containing medium-chain triglycerides to provide ketone bodies as an alternative source of energy for aging neurons.
Other natural supplements that have demonstrated efficacy in improving cognitive function include Senilife®, which contains a combination of phosphatidylserine, Ginkgo biloba, resveratrol, and vitamins E and B6; Activait®, which contains phosphatidylserine in combination with α-lipoic acid, carnitine, fatty acids, glutathione, and other antioxidants; S-adenosyl methionine (Novifit®); and apoaequorin (Neutricks®), a calcium-buffering protein found in jellyfish.