When Behaviour Change Is a Medical Warning Sign

Sagi Denenberg, DVM, MRCVS, Veterinary Psychiatrist

A sudden or unexplained change in a dog’s or cat’s behaviour should never be dismissed as stubbornness, disobedience, spite, or simply “getting old.” Behaviour is one of the ways an animal’s brain and body communicate that something has changed. The first visible sign of illness may not be vomiting, lameness, weight loss, or another symptom that owners readily recognize as medical. It may be irritability, withdrawal, disrupted sleep, house soiling, aggression, restlessness, reduced tolerance of handling, or a loss of interest in familiar activities.

This does not mean that a medical disorder causes every behaviour problem. Behaviour develops through a combination of genetics, early experience, learning, environment, relationships, and current emotional state. However, a medical condition can cause a new behaviour problem, worsen an existing one, or reduce an animal’s ability to cope with situations that were previously manageable. A behavioural assessment that ignores physical health is therefore incomplete.

Pain is one of the most important and commonly missed medical contributors. Animals do not always limp, cry, or show an obvious injury. Chronic pain may instead appear as reluctance to be touched, difficulty settling, reduced play, avoidance of stairs, altered sleep, increased vigilance, irritability, or aggression when approached or moved. A dog with spinal pain may growl when someone reaches for the collar. A cat with osteoarthritis may stop using a high-sided litter box, avoid being picked up, or withdraw from family interactions. In 2020, Mills et al. described the close and sometimes complex relationship between pain and problem behaviour in cats and dogs. Pain can directly trigger defensive behaviour, increase anxiety, and make an animal more sensitive to ordinary environmental stressors. 

The relationship can also work in both directions. Anxiety and chronic arousal can increase muscle tension, disrupt sleep, and amplify the experience of pain. An animal may then enter a cycle in which pain increases fear and irritability, while stress further lowers the threshold for discomfort and reactivity. Treating only the visible behaviour may therefore produce limited improvement when the underlying pain remains unrecognized.

Neurological disease can also present primarily as behaviour change. Seizure disorders, intracranial disease, inflammation, trauma, and other neurological conditions may cause episodic fear, altered awareness, staring, repetitive movements, sudden aggression, confusion, vocalization, or changes in social behaviour. Some episodes are subtle and may be mistaken for attention-seeking or unusual habits. Video recordings and a detailed description of when the episodes occur, how long they last, and what happens before and after them can be extremely valuable to the veterinarian.

Age-related cognitive decline is another important consideration. Older cats and dogs may become disoriented, wake repeatedly at night, vocalize without an obvious trigger, forget previously learned routines, soil indoors, become unusually dependent, or appear less interested in social contact. In 2012, Landsberg et al. explained that cognitive dysfunction is a progressive disorder of brain ageing and that diagnosis requires the exclusion of other medical conditions that can produce similar signs. An older dog pacing at night may have cognitive dysfunction, but pain, urinary urgency, gastrointestinal discomfort, sensory decline, endocrine disease, or medication effects may produce a similar pattern.

Changes in hearing or vision can alter behaviour even when the animal otherwise appears healthy. A dog with declining hearing may startle when touched because approaching footsteps are no longer detected. A cat with impaired vision may avoid certain rooms, become less confident when jumping, or react defensively when approached quickly. Sensory loss can also increase dependence on familiar routines and make environmental changes more difficult. Punishing a startled or defensive response in this context does not address the cause and may increase fear.

Urinary and gastrointestinal disorders frequently affect behaviour. A cat urinating outside the litter box may have cystitis, kidney disease, diabetes, arthritis, constipation, or another condition that changes urgency, comfort, mobility, or litter-box access. A dog asking to go outside repeatedly, waking at night, or becoming restless may be experiencing urinary urgency or gastrointestinal discomfort rather than a training failure. House soiling should therefore be treated as a clinical sign until relevant medical causes have been considered.

Endocrine and systemic disease can also change activity, sleep, appetite, arousal, and emotional stability. Hyperthyroidism in cats may contribute to restlessness, increased vocalization, irritability, and disrupted sleep. Disorders that cause weakness, nausea, breathing difficulty, excessive thirst, or altered metabolism can change how an animal responds to handling, exercise, separation, other animals, and everyday demands. Medication adverse effects and interactions must also be considered, particularly when behaviour changes soon after a drug is started, stopped, or adjusted.

The timing of the change is clinically important. A behaviour that appears suddenly in a previously stable animal deserves particular attention. So does a marked escalation in an established problem, a new reaction to touch, a change associated with eating or elimination, or a behaviour that occurs at a predictable time of day. Owners should record what happened, where it occurred, who was present, what the animal was doing immediately beforehand, and how long recovery took. Changes in appetite, drinking, movement, sleep, grooming, elimination, and social interaction should be documented at the same time.

A normal physical examination does not always exclude a medical contribution. Some sources of pain are intermittent or difficult to detect during a brief clinic visit. Neurological episodes may not occur during the appointment. Cats may suppress signs of discomfort in an unfamiliar environment. Diagnostic testing, imaging, specialist assessment, or a carefully monitored treatment trial may be required. The appropriate investigation depends on the animal’s age, history, physical findings, and pattern of behaviour.

It is equally important not to assume that finding a medical condition fully explains the behaviour. A dog may have pain and also have learned that growling makes people move away. A cat may have experienced urinary pain and then continue avoiding the litter box after the inflammation improves because the box has become associated with discomfort. Medical treatment and behavioural management often need to proceed together.

The practical message is simple. When behaviour changes, ask what has changed in the animal, not only what the animal is doing wrong. Early veterinary assessment can identify treatable disease, prevent unnecessary punishment, and improve both welfare and safety. Behaviour is not separate from health. It is part of health.

If your dog or cat is showing a sudden, unexplained, or concerning change in behaviour, we are here to help.

References

Landsberg, G. M., Nichol, J., and Araujo, J. A. 2012. Cognitive dysfunction syndrome: A disease of canine and feline brain aging. Veterinary Clinics of North America: Small Animal Practice, 42, 749–768. https://doi.org/10.1016/j.cvsm.2012.04.003

Mills, D. S., Demontigny-Bédard, I., Gruen, M., Klinck, M. P., McPeake, K. J., Barcelos, A. M., Hewison, L., Van Haevermaet, H., Denenberg, S., Hauser, H., Koch, C., Ballantyne, K., Wilson, C., Mathkari, C. V., Pounder, J., Garcia, E., Darder, P., Fatjó, J., and Levine, E. 2020. Pain and problem behavior in cats and dogs. Animals, 10, 318. https://doi.org/10.3390/ani10020318