Medical problems causing behavioral signs

Medical problems can have a direct effect on behavior or may play a contributory role in how a pet might behave in certain situations or respond to specific stimuli. The effects of the interplay of health and behavior on the individual may be influenced by genetics, age, type of health problems, and environmental variables, including stimulus qualities, the environment, learning, whether the pet is leashed, tied, or cornered, whether the pet is in possession of a favored resource, or the presence of other family members or pets. Signalment is an important consideration since, for example, the onset of behavior problems in older pets may increase the suspicion of a medical cause (see Chapter 13). Since medications can also affect behavior, any drugs or natural products that are being administered should be evaluated to determine if they might in any way be affecting the pet’s behavior.

In general the DAMNIT-B acronym applies to the possible medical causes of behavioral signs as it does for most other medical disorders (Box 6.1). However, additional categories have been added for behavioral disorders that may have similarities to behavioral pathology and psychiatric disorders in humans based both on their similar signs and response to drug therapy. These might have a genetic cause but often are multifactorial in that neonatal effects, early experience (including maternal deprivation and environmental isolation), nutrition, health, socialization, learning, and consequences may all play a role.

Medical contributing factors – the threshold effect

Although health issues can directly affect behavior, such as when diabetes or cystitis incites housesoiling or pain leads to aggression, the threshold theory (as in dermatology when multiple subclinical pruritic stimuli combine to cause clinical pruritus) also likely applies to behavioral problems, since multiple stimuli can combine to push the pet beyond a threshold to where a behavior problem is exhibited. Medical conditions might also lower the pet’s threshold or level of tolerance. This is especially important in senior pets where concurrent organ decline, sensory decline, painful conditions, age-related nervous system pathology, or other health issues can all affect behavior (see Chapter 13). For example, a dog that has a healthy relationship with other dogs in the house may become more irritable with painful conditions, such as dental disease or otitis, and avoid interactions or perhaps communicate with the other pets using visual signals and body postures to stay away. However, should the pet develop sensory decline (auditory or visual), it may resort to aggression to keep the other dogs away if its opportunity to avoid and signal is lost. Similarly, other pets may be confused by alterations in communication by the pet that is sick, ill, or unable to respond to signals due to sensory loss or declining mobility. Hyperthyroid cats might be more irritable and hence more likely to spray if exposed to the sights, sounds, or odors of new cats on the property.

When medical problems are diagnosed and treated and the behavior problem is not fully resolved this may be an indication that there are multiple factors contributing to the problem. One possibility is that during the course of the medical problems new behaviors have been learned. For example, if the pet becomes aggressive when approached, due to pain or discomfort (e.g., from otitis or arthritis), the aggression may continue after the pain is treated if the pet has learned that aggression successfully leads to retreat of a threat or control of social situations. In addition, if the pet with a painful condition has learned that someone touching it results in pain, it may continue to be guarded about any hand movement toward it long after the pain has subsided in anticipation that touch might still trigger pain. Another example is the pet that begins to soil in new locations due to lower urinary tract disease or diabetes, and subsequently learns new surface and location preferences.

Primary behavior problems

Assuming all medical causes have been ruled out or resolved, the assumption would be that the problem is behavioral and that the cause is likely some combination of genetics (nature) and environment (nurture). However, the problem is complicated by the fact that medical problems cannot always be entirely ruled out by diagnostic tests alone and that stress can have an impact on both health and behavior (discussed below). A therapeutic response trial may therefore be a useful or necessary test to rule out pain, seizures, or pruritus or to determine whether normalizing endocrine levels lead to a resolution in clinical signs. Alternately, if a compulsive disorder is suspected (see Chapter 11), a significant therapeutic response to clomipramine or fluoxetine might be diagnostic. In all cases, the practitioner should work to identify any underlying stress and provide appropriate guidance, since even if stress does not play a role in the problem that is being evaluated, it is still in the pet’s and owner’s best interest with respect to health and welfare to address it.

Neurology and behavior

Behavior changes can be associated with forebrain lesions. A change in personality or mood, inability to recognize or respond appropriately to stimuli, and loss of previously learned behaviors might be indicative of forebrain involvement. Alterations in awareness, responsiveness to stimuli and consciousness might arise from any disease that involves the brainstem or forebrain. Altered responsiveness to stimuli can also arise from sensory or motor dysfunction. The limbic system is associated with emotion so diseases affecting it, including areas such as the hypothalamus, can also affect behavior.⁵

Diseases and degenerative processes of the special senses may initially present solely with behavioral signs. Sensory decline should be a consideration in pets with anxiety, increased vocalization, altered appetite, increased irritability, decreased or heightened responsiveness to stimuli, decreased responsiveness to learned commands, or changes in behavioral responses to people or other animals.

Diseases that affect the central nervous system and result in abnormal behavior may be intracranial in origin (e.g., congenital, neoplastic, degenerative, traumatic, circulatory) or may also be extracranial (e.g., infections (feline infectious peritonitis, rabies, toxoplasmosis), toxins, metabolic diseases, hepatic encephalopathy, endocrinopathies, compromised blood flow, cardiac disease, anemia, hypertension, medication, or illicit drugs). Cats with feline immunodeficiency virus may develop deficiencies in learning new tasks, loss of socialization, decreased grooming, housesoiling, aggressive behaviors, dementia, disorientation, polyphagia, stereotypies, decreased sleep, and overall more abnormal behaviors with more severe signs than in a control group of cats.^6,7 Rapid-eye-movement sleep movement disorders, which might include signs of panic, howling, barking, growling, chewing, aggression, or violent limb movements during sleep, have been diagnosed in dogs.^8,9 There is also an age-related decrease in cognitive function with a wide array of behavioral signs related to brain aging. This is discussed in detail in Chapter 13. While there may be identifiable medical signs associated with serious neurologic problems, including alterations in mental status (stupor, coma), cranial nerve and sensory deficits, seizures, tremors or motor deficits (gait abnormalities), or signs of weakness, altered appetite, drinking, and elimination or emesis, this is not always the case.

Generally, seizure episodes are recurrent, intermittent, repetitive, and abnormal, and have a normal interictal period. In humans, temporary lobe epilepsy or partial (focal) seizures of the temporal lobe can have behavioral signs, including mood alterations, and visual, auditory, gustatory, olfactory, and somatic hallucinations. These may be associated with ictal, postictal, or perhaps even interictal stages. There may also be comorbidity of behavioral signs with epilepsy or with the drugs used for treatment.^10–12 Simple partial seizures do not have altered consciousness while partial complex seizures may have altered levels of consciousness and may have a behavioral component such as hallucination or aggression (“rage”).

Primary behavior disorders and behavior pathology such as compulsive disorders may also be present, which can be difficult to differentiate from seizure disorders. Differentiating a medical from a behavioral cause can be particularly challenging when pets present with air snapping, tail chasing, pouncing, fixed staring, star gazing, head shaking, spinning, checking, or tremors. Another group of signs include the head tremors of boxers, bulldogs and Doberman pinschers, and more generalized idiopathic tremors such as those seen in “white shaker dogs” and in great Danes.¹³ The interrelationship between behavior and health is further demonstrated in the Scottish terrier with Scotty cramp, a nonpainful disease that causes muscle tonicity with increasing activity, which generally resolves after rest. The cause may be a deficiency in serotonin in the spinal cord. In fact, in a recent case study, treatment with fluoxetine was effective at reducing signs at a dose of approximately 1 mg/kg bid.¹⁴

A therapeutic response trial with phenobarbital, potassium bromide, levetiracetam, gabapentin, carbamazepine, or perhaps clonazepam (cats) may rule out a possible seizure focus as a cause. However, since many of these drugs might also reduce anxiety or neuropathic pain, an improvement in clinical signs may prove to be an effective component of treatment, but it does not necessarily confirm a seizure as a diagnosis.

Endocrine effects on behavior

Endocrine diseases, including hyperthyroidism, hyperadrenocorticism, and hypothyroidism can also contribute to anxiety. Hypothyroidism may increase serotonin turnover so that behavior changes may be due to alterations in serotonergic activity.^15,16 Since cortisol inhibits thyroid-stimulating hormone release, stress can also diminish thyroid levels. In humans, abnormalities in the metabolism of thyroid hormones appear to be important in mood disorders, and triiodothyronine has been used to augment the effects of antidepressant therapy.¹⁷ However, unless low thyroid levels can be documented, thyroid hormone replacement therapy is unlikely to be indicated and might lead to elevated thyroid levels.¹⁸ In fact, supplementation with thyroid can exacerbate irritability and arousal in cases where thyroid supplementation is not indicated or where excessive doses are used. In one study, dogs with behavioral problems were found to have higher levels of total thyroxine than control dogs.¹⁹

Gastrointestinal and ingestive disorders and behavior

Commonly reported behavior signs that might have a medical cause include polyphagia, hyperphagia, polydypsia, coprophagia, grass and plant eating, increased begging, garbage (trash) raiding, and stealing. Both medical problems and medications could cause or contribute to the problem. Medications that might increase ingestion (drinking or appetite) include corticosteroids, diuretics, and benzodiazepines, while appetite might be suppressed by some medications such as fluoxetine, cyclosporine, ketoconazole, or any medication that might cause gastrointestinal upset. Renal and hepatic diseases, diabetes insipidus, diabetes mellitus, and hyperadrenocorticism may be associated with increased eating or drinking. Similarly, pets on calorie restriction for weight loss may have a dramatic increase in appetite. Pets with polyphagia may beg, steal, raid garbage, or even develop coprophagia or picas.

For pets presented with coprophagia and grass eating, gastrointestinal, nutritional, and metabolic disorders should first be ruled out; however, both of these behaviors could be normal for the individual. Although it has been suggested that pets may eat grass or plants due to gastrointestinal upset, in one survey of 1571 owners of dogs that ate plants or grass, less than 10% of owners reported their pet to appear ill before eating plants.²⁰ Although most pets with coprophagia have no underlyng health concerns, pets that eat stools (especially their own) should first be evaluated for possible medical issues by determining if there is abnormal stool consistency, volume, or frequency; signs of polyuria, polydypsia; and a normal body condition score. Pets with exocrine pancreatic insufficiency or other causes of malassimilation may have steatorrhea, and stools that are soft and voluminous with incomplete food digestion. The pet is often underweight, with a ravenous appetite.

Most coprophagia is likely a result of normal behavior evolved to maintain environmental cleanliness. Dogs that are hungry or greedy eaters are most commonly affected.^21,22 Food additives are unlikely to be effective. For more details see Chapter 10.

Unusual oral behaviors, including licking, sucking, pica, and smacking lips, or gulping, can be compulsive behavioral disorders but medical differentials would include partial (focal) seizures and gastrointestinal disorders. In a recent study of dogs with excessive licking of surfaces, gastrointestinal disorders, including eosinophilic and lymphoplasmacytic infiltration, delayed gastric emptying, irritable bowel syndrome, giardiasis, pancreatitis, and gastric foreign bodies were identified, and clinical signs in 9/17 dogs were completely resolved after medical treatment.²¹

The presence of gastrointestinal signs, including anorexia, hyporexia, colitis, emesis, dyschezia, increased volume of stool, stool color changes, or diarrhea, might support a medical cause of the signs. Gastrointestinal diagnostics and a therapeutic trial with a hydrolyzed protein diet, a low-fat reduced-residue diet, a novel protein diet or proton pump inhibitors or gastrointestinal protectants might be required to rule out potential medical causes. Picas may also be a compulsive disorder that might have a genetic basis in some individuals. For diagnosis and treatment of picas, see Chapters 10 and 11.

Medical causes of housesoiling

Housesoiling can often be precipitated by medical problems. In a retrospective study of cats with problem elimination behavior, 60% of the cats had a history of feline urologic syndrome/feline lower urinary tract disease.²³ Inappropriate elimination can be due to any medical problem that causes an increased volume of urine or stool, increased discomfort during elimination, decreased control, or diseases that affect cortical homeostasis. On the other hand, urinary tract disease is unlikely to be a factor in urine marking in cats.²⁴ However, systemic illnesses leading to behavioral signs could contribute to marking in dogs or cats by altering hormonal states or increasing anxiety. Assessment of every elimination disorder should therefore begin with a physical examination, complete blood count, biochemical profile, and urinalysis, as well as any other imaging or endoscopic procedure that might be indicated. In marking cats, evidence of masculinization such as penile barbs or odorous urine which might be indicative of a hormonal disorder might indicate that further hormonal assessment is warranted. In one study, a number of castrated dogs and cats were diagnosed with extratesticular tumors; some of those animals presented with intact male sexual characteristics.²⁵ Therefore when marking or other sexual behaviors arise in dogs or cats, examination for a scrotal mass and testosterone levels in response to gonadotropin-releasing hormone response test should be a consideration. See undesirable sexual behaviors in Chapter 14 for details.

Medical causes of self-trauma

Self-traumatic disorders, including biting, chewing, scratching, licking, or excessive barbering, can lead to skin lesions and alopecia. Medical differentials include diseases that lead to pain or pruritus (e.g., hypersensitivity reactions, neuropathies, symmetrical lupoid onychodystrophy), infections (e.g., bacterial, fungal, parasitic), infestations, endocrinopathies, tumors, immune-mediated diseases, neoplasia, or skin disorders associated with systemic diseases (e.g., hepatocutaneous syndrome). When there are no primary lesions, and the problem is nonseasonal, behavioral presentations (tail mutilation, nail biting, psychogenic alopecia, acral lick dermatitis, face and neck scratching, regional or generalized pruritus, and flank sucking), it can be difficult to differentiate displacement behaviors and compulsive disorders from medical causes. In a study of 21 cases referred for psychogenic alopecia, 76.2% had a medical etiology.²⁶ A combination of adverse food reaction and atopy (6 cases) was the most common diagnosis. Some cats with histologically normal skin still had a medical cause.²⁶ For acral lick dermatitis, adverse food reactions, deep pyoderma (which is often multidrug-resistant), and a variety of medical causes, including tumors, trauma, and protozoal and fungal infections may all be factors.^27,28 For claw (nail) biting in dogs, immune, inflammatory, or infectious causes including Malassezia must first be ruled out.

Feline hyperesthesia is a presenting complaint that may arise from any number of medical or behavioral causes, including dermatologic diseases, spinal disease, feline leukemia virus-induced myelopathy, complex partial seizures, pain and neuropathic pain, compulsive disorders, and any condition leading to behavioral arousal. Clinical signs may also include dilated pupils, twitching skin, biting at the tail, rippling along the back, excessive grooming, biting, and licking, and behaviors associated with high arousal, including anxiety, aggression, restlessness, running, defecation while running, and vocalizing. In fact, studies show that in some cases pain pathways may be overly sensitive to relatively innocuous touch sensations.²⁹ Feline oral facial pain syndrome may present with repetitive chewing and licking behaviors as well as pawing and self-mutilation. For further details on differentiating dermatologic from behavioral disorders, see Chapter 11.

Drugs and behavioral effects

Since drugs are utilized for improving health or behavior, often a resolution in behavioral signs or positive effects will be achieved. However, therapeutic effects, side-effects, and adverse effects of medications can also contribute to changes in behavior that may or may not be the intended, desired, or expected effect. Antihistamines such as diphenhydramine might sedate or could have a paradoxical effect of increasing restlessness or agitation; similarly, cyproheptadine generally increases appetite and might sedate but can also occasionally lead to a paradoxical increase in agitation. Drugs that have an anxiolytic effect such as benzodiazepines or buspirone may disinhibit some behaviors, leading to an increase in aggression in cases where fear might have been inhibiting the aggressive response. In addition, benzodiazepines might sedate, increase appetite, or cause paradoxical agitation and restlessness. Mirtazapine, a tetracyclic antidepressant, is most commonly used in pets as an appetite stimulant and antiemetic which might also calm or sedate; however it may lead to increased agitation and vocalization, especially in cats. While tricyclic antidepressants and selective serotonin reuptake inhibitors are less likely to lead to disinhibition, they can have variable effects on behavior, including anorexia, the potential for urine retention, or sedation in the more anticholinergic or antihistaminic antidepressants, or a more activating effect with fluoxetine. Corticosteroids might be expected to cause behavior changes, including polydypsia and polyphagia. These could contribute to begging, food stealing, pica, soiling, night waking, and panting. In one preliminary study of dogs treated with corticosteroids, owners reported increased nervousness and restlessness (6), irritable aggression (4), increased startle responses, food guarding or avoidance (3 each), and decreased activity or barking (2 each) in 11 of 31 dogs.³⁰ Excess thyroid supplementation might contribute to increased anxiety, restlessness, reactivity, weight loss, and possible aggression.

Pain management and assessment

One might wonder why the topic of pain management would appear in a text on veterinary behavior. First and foremost, the issue of humane care and the alleviation of pain and suffering should be a critical issue in any discussion of pet care. Specifically, however, pain assessment, response to pain medications, and the overall well-being of the pet depend heavily on the measurement and assessment of the pet’s behavior.³¹ In addition, a wide range of behavior problems, ranging from avoidance, decreased activity, and inappetance to irritability, restlessness, and aggression could be due to underlying pain. In fact, any change from normal behavior and the development of new and abnormal behaviors can also be due to underlying pain or disease.

For veterinary practitioners, there are three areas of pain management on which to focus: (1) assessment in the hospital; (2) owner monitoring and assessment after hospitalization or surgery; and (3) owner measures to identify the onset and progress of pain, especially chronic disease states such as degenerative joint disease. In addition, separate measures are often required for dogs and cats, thus requiring up to six different measures or scales. While pain assessment should combine physical examination, diagnostic tests, and behavioral signs, there may be little to no correlation between objective and subjective measures.^32,33 Therefore behavioral measures are often the primary determinant.

Behavioral pain assessment: diagnosis and monitoring

The fact that behavior is a critical component of pain assessment and monitoring should not be surprising since pain is defined as “an aversive sensory and emotional experience which elicits protective motor actions and results in learned avoidance and modification of behavior traits including social behavior” (iasp-pain.org). However, since animals have adaptive mechanisms which may mask signs of pain, an absence of painful behaviors does not necessarily mean an absence of pain. Therefore, to address pain in pets adequately, veterinarians and owners should begin with the assumption that procedures and medical conditions that are painful in humans would cause similar pain in pets.

While physical examination and physiologic measures may be useful to identify certain types of pain, behavioral measures, including the absence of normal behaviors or the expression of abnormal behaviors, may be of greater importance in diagnosing and monitoring some forms of pain³⁴ (Table 6.2). Numerous studies have found that subjective behavioral measures are an accurate means of measuring pain and assessing efficacy of therapeutics.^33,35,36 However, since changes in behavior may be subtle and easily missed, veterinarians must take a proactive approach in: (1) educating staff on procedures and methods for pain monitoring; (2) informing pet owners about monitoring and management of pain after hospital discharge; and (3) advising pet owners about the potential significance of any change in behavior or emergence of abnormal behaviors.

Table 6.2 Signs of pain in dogs and cats

Depending on the cause of pain, individual and breed differences, and whether the pain is acute or chronic, clinical presentation will vary. Pain may arise from cardiopulmonary, oncologic, dermatologic (otic), dental, gastrointestinal (inflammatory bowel disease, hepatitis, pancreatitis), musculoskeletal, ocular, urogenital, neurologic, iatrogenic (e.g., surgical procedures), and traumatic causes. Each of these may be associated with clinical signs that are specific to the area of the body or organ system involved. For example, dental pain may affect eating and can usually be found on physical examination; pain associated with anal pruritus or anal sacculitis may be accompanied by licking or “scooting” the rear along the ground; pain associated with otitis, traumatic injury, glaucoma, or even spinal disease might be identified by physical examination and medical diagnostics; while inflammatory bowel disease and bladder disease might be associated with a change in elimination behaviors and is identifiable on physical examination and stool or urine analysis. Conversely, some painful conditions such as degenerative joint disease in cats may have solely behavioral signs with poor correlation to findings on radiographs or clinical examination.^37,38

While a number of assessment tools have been proposed for evaluation of acute and chronic pain in dogs and cats, many of the current methods are still in need of further refinement and validation.³⁹ However, this does not mean that the practice should wait to implement pain scoring until fully validated and standardized protocols are published. Instead the practice should select pain assessment measures for in-hospital use, patient discharge, and ongoing evaluation based on the latest available data and what might be most practical for staff and clients. Modifications can then be made as needed based on the latest available data. In a recent survey over 80% of veterinary nursing staff felt that pain-scoring tools would be useful but only 8.1% of practices utilize a scoring system.⁴⁰