Merck Manual

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Medical Causes of Behavioral Signs

Medical Causes of Behavioral Signs

Medical Condition

Behavioral Signs

Illness or disease

Altered personality, lethargy, depression, withdrawal, anorexia, reduction in grooming, altered social relationships, altered response to stimuli


Central (affecting forebrain, limbic/temporal, and hypothalamic), rapid-eye movement sleep disorders

Altered awareness and response to stimuli, loss of learned behaviors, housesoiling, disorientation, confusion, altered activity levels, temporal disorientation, vocalization, change in temperament (fear, anxiety, aggression), altered appetite, altered sleep cycles, interrupted sleep (aggression/waking/activity)

Peripheral (neuropathy)

Self-mutilation, irritability, aggression, circling, hyperesthesia

Focal seizures/temporal lobe seizures

Repetitive behaviors, self-trauma, chomping, staring, altered temperament (eg, intermittent states of fear or aggression), tremors, shaking, interrupted sleep

Sensory dysfunction

Altered response to stimuli, confusion, disorientation, altered sleep cycles, irritability, aggression, vocalization, housesoiling

Metabolic / Endocrine

Feline hyperthyroidism

Irritability, aggression, urine marking, increased activity, night waking

Canine hypothyroidism

Lethargy, decreased response to stimuli, irritability, aggression


Panting, night waking, housesoiling, irritability, polyphagia, anxiety


Housesoiling, night waking

Functional ovarian and testicular tumors

Androgen-induced behaviors: males—aggression, roaming, marking, sexual attraction, mounting; females—nesting or possessive aggression of objects

Hepatic or renal encephalopathy

Signs associated with affected organ, anxiety, irritability, aggression, altered sleep, housesoiling, mental dullness, decreased activity, restlessness, increased sleep, confusion

Anemia or electrolyte imbalances



Altered response to stimuli, decreased activity, restlessness/inability to settle, vocalization, housesoiling, aggression, irritability, self-trauma, waking at night


Licking, polyphagia, pica, coprophagia, housesoiling (fecal), wind sucking, tongue rolling, unsettled sleep, restlessness


Housesoiling (urine), polydipsia, waking at night


Psychogenic alopecia (cats), acral lick dermatitis (dogs), nail biting, hyperesthesia, other self-trauma