BEHAVIOR PROBLEMS IN THE GERIATRIC DOG AND CAT

Gary Landsberg, BSc, DVM, Diplomate ACVB
Doncaster Animal Clinic, Thornhill, Ontario

For details on Geriatric Behavior Problems and their treatment in dogs and cats see

When a practitioner is presented with a geriatric pet with a behavior problem, the first diagnostic challenge is to identify any and all underlying medical conditions that could be contributing to the behavioral changes. A good knowledge of geriatric medicine and the potential behavioral changes associated with aging and disease is therefore essential. Although the undesirable behavior could have an entirely medical or behavioral cause, it is the combined effects of the environment, learning, and health that determines the pet’s behavior.

The threshold theory, as it applies to dermatology, is that each animal will tolerate a certain level of pruritic stimuli without itching. However, when the stimulus exceeds the threshold, or when multiple stimuli (e.g. allergens) act in combination to cause the threshold to be surpassed, pruritus may be exhibited. Behavior problems may also be exhibited when a number of stimuli are present that "push" the pet beyond a certain threshold, or when medical conditions lower the threshold. This is especially important in the aging pet, where organ decline, sensory decline, degenerative conditions, age related CNS pathology, and an increasing number of medical problems, all impact on a pet’s behavior. For example, the pet that is fearful of children, may begin to become more reactive, irritable, and aggressive, as it becomes more uncomfortable (e.g. dental disease) or as it becomes less mobile (e.g. due to degenerative arthritis

CAUSES OF BEHAVIOR PROBLEMS IN THE AGING PET

With behavior problems of any age, but especially in cases with an older age of onset, medical problems must first be ruled out. In addition to medical problems, learning, environmental changes and genetics can all play a role in the onset and development of behaivor problems.

The aging process is associated with progressive and irreversible changes in the body systems. Although these changes are usually considered individually, the elderly pet is seldom afflicted with a single disease, but rather varying degrees of organ dysfunction. Any condition that is associated with pain or discomfort, can lead to increased irritability, an increased anxiety or fear of being handled or approached, and ultimately an increase in aggressive displays. Mobility may also be affected. The pet may therefore appear to be less responsive to commands or may become increasingly aggressive, choosing to threaten and bite, rather than retreat. A decrease in mobility could also affect elimination by reducing the pet’s desire or ability to utilize its elimination area. Sensory dysfunction can also lead to behavior changes. Organ decline and dysfunction, an increase in tumors, degenerative conditions, immune diseases, neurological deterioration, cognitive decline (see below) and endocrinopathies are more common in the aging pet, and can have profound effects on behavior. For example, disease or dysfunction of the urinary system can cause or contribute to incontinence or inappropriate urination because of increased volume or frequency, discomfort during urination or decreased control. Similarly diseases of the gastrointestinal tract causing colitis, diarrhea, constipation, discomfort during elimination, increased volume or frequency, or decreased control can lead to inappropriate defecation. Endocrine disorders resulting in overproduction or depletion of hormones can cause a variety of behavior changes ranging from lethargy and depression to irritability and agggression. And of course any disease process that directly effects the central nervous system can cause behavioral changes.

 

Aging, the Brain, and cognitive dysfunction

In dogs, cognitive dysfunction is defined as the occurrence of one or more geriatric onset behavior problems, which are not sufficiently accounted for by medical conditions. Some of these age related behavioral complaints include decreased interest in food, decreased ability to recognize places, people or other animals, generalized apathy, confusion or disorientation, disruption of the sleep-wake cycle, wandering, repetitive and compulsive disorders, persistent vocalization especially at nighttime, as well as an increase in housesoiling. A study of dog owners with dogs aged 11 years and older found that over 60% of owners reported one or more behavioral changes consistent with cognitive dysfucntion. (Ruehl W, Hart B.). In contrast, practitioner surveys revealed that only 7% of pet owners spontaneously, (without prompting) mention such problems to their veterinarian.(Ruehl W, Hart B). With respect to cats, preliminary results suggest that many of the behavioral changes typical of cognitive dysfunction in dogs also occur in eldery cats, but that the age of onset may be higher in cats. Unfortunately, most owners fail to discuss these geriatric onset behavior changes with their veterinarian, perhaps incorrectly assuming that they are an unfortunate but untreatable aspect of aging. It is essential therefore, that veterinarians address behavior issues and concerns with every client, regardless of the pet’s age.

The aging process is associated with progressive and irreversible changes in the body systems. The aging pet may be more sensitive to change as the capacity to adapt diminishes. In addition, as organ function declines and catabolic capacity decreases, the choice of drugs and their dosages may need to be adjusted. Since the physiological effects of aging on the brain can be subtle and slowly progressive, it may be difficult to differentiate physiological from pathological changes and normal from senility.

It is generally believed that, as in people, the cognitive ability of the dog and cat tends to decline with age.(Cummings et al, Milgram et al) Alzheimer type pathology including diffuse beta amyloid plaques within the brain and vessel associated amyloid, have been identified in geriatric humans, dogs, and cats.5 Plaques in the brain of dogs and cats are always of the diffuse type while plaques in humans often progress to the neuritic or mature type. Although atherosclerosis, cerebral ischemia and hemorrhage are rare in dogs and cats, the brain of the elderly pet may become chronically hypoxic due to decreased cardiac output, anemia, conditions that lead to hypertension (diabetes, hyperthyroidism, renal disease, cardiac or respiratory insufficiency) and arteriosclerosis of the non-lipid variety (due to arterial fibrosis, endothelial proliferation, mineralization, and amyloid deposition). With age there is cerebral atophy, ventricular dilation, lifopusicin accumulation, a decrease in the number of neurons, and an increase in glial cells.(Cauzinilee)

There are also a number of neurochemical changes associated with aging in a number of species, including a fall in serotonin levels, an increase in MAOB leading to a decline in dopamine, a decrease in cholinergic activity, and an adrenergic increase, (leading to a further decrease in cerebral perfusion).(Cauzinille) There is also an increased production and decreased clearance of free radicals.

A diagnosis of cognitive dysfunction generally requires the presence of one or more of the following behavioral changes in the absence of any physical causes: decreased reaction to stimuli, confusion, disorientation, decreased interaction with the owners, increased irritability, slowness in obeying commands, alterations in sleep-wake cycle, decreased responsiveness to sensory input, increased vocalization and problems performing previously learned behaviors such as housetraining.(Milgram et al, Ruehl, Hart)

Depletion of brain dopamine, at the level of the cerebral cortex, may be responsible for a number of the behavior changes associated with aging. The drug, L-deprenyl has several beneficial effects (see below) including selective inhibition of monamine oxidase type B (MAOB) thus helping to normalize dopamine levels which may become depleted in some cases of age related cognitive dysfunction. Since a fall in serotonin level may lead to sleeping problems, neuromuscular disorders, and decreased vigilance, serotonin reuptake inhibitors such as fluoxetine and paroxetine may be useful. Nicergoline an alpha adrenergic antagonist may also help to improve some of the behavioral signs of aging, primarily by increasing cerebral vascular blood flow.

 

Diagnosing behavior problems in the aging pet

For each behavior problem, a history, physical examination, and diagnostic tests (cbc, urinalysis and biochemical profile with T4 to start) will be needed to determine whether there are contributing medical problems. If there is no underlying medical cause, the behavioral history, with particular emphasis on the onset of the problem, is the key to making an accurate diagnosis. In some cases, such as the cat that is overgrooming, a purely behavioral cause cannot be established until all possible medical conditions have been ruled out either by diagnostic testing, or by drug or food trials.

 

L-Deprenyl

The drug L-deprenyl (Aniprylâ , Deprenyl Animal Health, Inc, Overland Park, KS) is licensed in Canada and the United States for the treatment of canine pituitary dependent hyperadrenocorticism as well as, in Canada, for canine cognitive dysfuntion. To date, there have been no published studies on the efficacy of L-deprenyl in geriatric cats, although there have been numerous anecdotal success stories. A small study found no toxicity in cats at up to 10 mg/kg (20 times the typical clincal dose), with the only side effects being occasional vomition and salivation (at the highest dose).(Ruehl, Griffin et al)

There are several ways L-deprenyl may help cognitive dysfunction in dogs and cats both symptomatically, and perhaps by slowing neurodegenerative disease progression. First, it enhances brain dopamine concentrations and metabolism through irreversible inhibition of MAOB. Since MAOB is responsible for the breakdown of dopamine, MAOB inhibitors help to maintain normal brain dopamine levels. Dopamine depletion at the level of the cerebral cortex may contribute to cognitive dysfunction. Second, L-deprenyl decreases free radical load by decreasing their production and increasing their removal. L-deprenyl also exerts neuroprotective effects, for which two mechanisms have been proposed. L-deprenyl may also decrease apoptosis (programmed cell death) of injured neurons and / or it may promote resynthesis of nerve growth factors. In humans L-deprenyl has been suggested to have some beneficial effects in Alzheimers disease.(Katzung) L-deprenyl should not be used concurrently with antidepressants, narcotics, or other MAO inhibitors, including amitraz. L-derpenyl is dosed at .5 mg/kg per day each morning and if there is not significant improvment within a month, the dose can be raised to 1 mg/kg per day. For pituitary dependent hyperadrenocorticism the dose is 1 mg/kg per day which can be raised up to 2 mg/kg per day if there is not significant improvment within 1 to 2 months.

 

REFERENCES

Cauzinille L. Ageing of the nervous system in Veterinary Medicine. In: Use of alpha-blocking agent Fitergol in the treatment of behavioural disorders in old dogs. Rhone-Merieux Publication, p.3-8

Cummings BJ, Satou T, Head E, et al. Diffuse Plaques contain c-terminal AB42 and not AB40: Evidence from Cats and Dogs, Neurobiology of Aging, 17, 4653-659,1996

Katzung BG. Basic and Clinical Pharmacology, 6th edition. Appleton & Lange, East Norwalk, Connecticut, 1995

Milgram NW, Ivy GO, Head E, et al: The effect of l-deprenyl on behavior, cognitive function and biogenic amines in the dog. Neurochemical Research 18:1211, 1993

Ruehl WW, Hart BL: Canine cognitive dysfunction. In Dodman NH, Shuster L, eds.: Psychopharmacology of Animal Behavior Disorders. Blackwell Science Inc., Boston (in press)

Ruehl WW, Griffin D, Bouchard G, Kitchen D. Effects of L-Deprenyl in Cats in a One Month Dose Escalation Study. Veterinary Pathology, 33, 5, 621, 1996

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