Help! My dog licks everything

2008-04-01
Valarie V. Tynes, DVM, DACVB

A dog's constant, repetitive licking of objects or surfaces is a problem whose frequency is difficult to determine. This licking may occur often, but because it seems harmless and may only be somewhat annoying, many owners accept this unusual behavior or simply ignore it. However, some owners will inquire about it during a routine checkup and ask for advice.

A dog's constant, repetitive licking of objects or surfaces is a problem whose frequency is difficult to determine. This licking may occur often, but because it seems harmless and may only be somewhat annoying, many owners accept this unusual behavior or simply ignore it. However, some owners will inquire about it during a routine checkup and ask for advice.

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Such owners often describe a dog that licks floors, carpets, walls, furniture, its own lips, and even the owner's legs, hands, or arms constantly. When not a result of an underlying medical problem, the behavior is unlikely to cause harm. However, if hair and fibers are ingested, constant licking can potentially result in life-threatening intestinal blockage that requires surgical intervention.

This article will help you identify the reason a dog licks surfaces excessively and treat this condition. I only focus on the licking of surfaces in the environment and do not cover excessive self-licking, such as that resulting in acral lick dermatitis.

DEFINING THE PROBLEM

The first and most important step when presented with a dog that licks excessively is to define the behavior as accurately as possible. Excessive licking must be differentiated from pica. An observant owner can usually describe exactly what behavior the dog is performing. Some dogs may exhibit the behavior in the veterinary clinic, but their tendency to do so or not is unlikely to be diagnostic. If there is any doubt about what behavior the dog is performing, videotaping the dog in its home can be useful. Instruct clients to collect 10 to 15 minutes of their dogs performing the behavior, both with and without the owners interrupting the behavior.

Although some dogs may only lick objects excessively, others may exhibit pica and excessive licking as part of the same set of behaviors. The potential medical causes and treatment of pica have been well-covered elsewhere, so they are not included here.1

HISTORY

Once you have determined that the problem is limited to excessive licking, collect a thorough history, including the age of onset, the length and frequency of licking episodes, any changes in the frequency or intensity of the behavior, and any stimuli that appear to lead to the behavior (see "Ask owners to keep a record of behavior problems"). If no external stimuli appear to provoke the behavior and it is a relatively new behavior, then a medical cause may be likely.

Ask owners to keep a record of behavior problems

Ask clients if the behavior can be interrupted, and if so, how do they interrupt it (yelling, physically stopping the behavior, chasing the animal away). A behavior that is difficult to interrupt may be more likely to be caused by a medical condition that causes distress than is a behavior that is easily interrupted. However, a true compulsive disorder that has been present for months or years may also be difficult to interrupt. Once interrupted, how long before the dog begins licking again? A dog that immediately returns to licking after a brief interruption may be in physiologic distress or demonstrating a compulsive disorder.

Collect information pertaining to the dog's general behavior and temperament to help determine if the dog has a history of anxiety or other repetitive behaviors and under what circumstances they have occurred. If possible, the owner should also try to determine if any related animals exhibit similar repetitive behaviors. Stereotypies and many medical conditions may have a genetic basis (e.g. seizures), so identifying related animals with similar behaviors may help narrow the differential diagnoses list.

Ask owners how their dogs spend a typical day, including how much and what type of interactions the pets have with individuals and other pets living in the household. A lack of exercise or unpredictable or frightening interactions with people or animals are situations that could lead to anxiety, conflict, or frustration, resulting in a behavior problem. In addition, note any changes in the environment or owners' schedules since such changes can also contribute to behavior problems.

Finally, nausea is a common cause of excessive licking of surfaces, so a detailed history should include questions about the dog's diet (type, amount, and frequency fed), treats, and table scraps and any medications or supplements the dog is receiving. Do not assume that since you have not prescribed any medications lately, the dog is not receiving anything that would make it nauseated. It is increasingly common for owners to give their pets supplements, table scraps, raw meat, or bones and not think it is important enough to mention to you.

If medications have been prescribed recently, be aware of which ones are likely to cause nausea, especially when given on an empty stomach. Many oral medications, such as nonsteroidal anti-inflammatory drugs, metronidazole, and griseofulvin, can lead to nausea. In addition, many oral antibiotics, such as cephalosporins, penicillins, tetracycline, and erythromycin, can cause gastrointestinal upset, especially if given on an empty stomach. Always ask clients whether they are giving these medications with food.

NARROWING THE LIST OF DIFFERENTIAL DIAGNOSES

Differential diagnoses for excessive surface and object licking include2

  • Diseases that cause nausea or gastrointestinal discomfort (e.g. liver disease, exocrine pancreatic insufficiency, inflammatory bowel disease, intestinal lymphosarcoma)

  • Dental or oropharyngeal pain or discomfort

  • Adrenal disorders (hypoadrenocorticism or hyperadrenocorticism may cause excessive licking because of nausea, electrolyte disturbances, or polyphagia)

  • Appetitive behavior (possibly as a result of mild polyphagia)

  • Primary central nervous system disturbances (e.g. hydrocephalus, brain neoplasia, partial motor seizures)

  • Attention-seeking behavior

  • Anxiety

  • Conflict- or frustration-induced displacement behavior

  • Compulsive disorders

  • Canine cognitive dysfunction.

Initial examination and diagnostic tests

Perform a physical examination, including a neurologic examination, in all dogs presented for excessive licking. In addition, perform a complete blood count, serum chemistry profile, fecal examination, and urinalysis.

Additional diagnostic tests

If the results of the initial examinations and tests are normal but you still suspect liver disease, measure fasting and two-hour postprandial total serum bile acid concentrations to detect occult liver disease.3

If the results of the initial tests are all normal but clinical signs suggestive of Cushing's syndrome are present, consider measuring a urine cortisol-creatinine ratio.4

In addition, measure fasting serum concentrations of trypsin-like immunoreactivity, cobalamin, and folate to rule out exocrine pancreatic and small intestinal disorders.5 If the results of these tests are normal, consider a hypoallergenic diet trial to rule out dietary intolerance or hypersensitivity.5

If the history, clinical signs, and signalment are still strongly suggestive of a medical cause for the excessive-licking behavior, ultrasonography and possibly gastrointestinal contrast studies may be indicated to rule out conditions such as neoplasia.

Primary neurologic problems such as hydrocephalus or brain tumors should be ruled in or out based on an animal's age and breed, the presence or absence of other neurologic problems, and, in the case of a brain tumor, the progressive nature of the condition. A diagnosis of neurologic problems will be more likely if the licking behavior is virtually impossible to interrupt and if, while licking, the dog acts as if it is unaware of its surroundings. With partial seizures, the owners, with thorough questioning, may also describe preictal and postictal periods associated with the surface licking behavior.6

Narrowing testing because of financial constraints

Many clients have financial constraints that limit the diagnostic tests that can be done on the first visit. However, a patient's signalment, history, and other factors can guide you in determining whether a medical or behavioral cause is more likely.

Age. If the dog is middle-aged or older, evaluate medical causes most closely. If the licking behavior appears suddenly in a geriatric dog, question the client closely about other clinical signs suggestive of cognitive dysfunction. In my opinion, it is unlikely for a middle-aged or older dog with a placid temperament and no history of anxiety-related behaviors to suddenly develop a stereotypy or compulsive disorder. Most repetitive behaviors in people develop at or before adolescence.7 Barbering in mice and feather plucking in psittacines (behaviors that are being considered as possible models for some human repetitive disorders) develop before or around the time of sexual maturity.8,9 Although it is possible that an adult animal might experience an event leading to an anxiety- or conflict-related disorder (e.g. displacement or redirected behavior), in older animals, consider a medical cause more likely than a compulsive disorder.

Breed and temperament. Many breeds may have a genetic predisposition for certain compulsive disorders (Table 1).10 Although excessive licking of surfaces is not a compulsive disorder that has been observed more in a particular breed, a dog that is susceptible to one type of oral compulsive behavior may be at risk for other anxiety-related behaviors. In addition, in my opinion, some dogs are born with a shy or fearful temperament that can predispose them to anxiety-related behaviors when faced with frustrating or conflicting experiences. So when presented with a dog that has a history of other anxiety-related behaviors, a behavioral cause for the licking could reasonably be moved higher on the differential diagnosis list.

Table 1: Breed Predilections for Compulsive Behaviors*

Persistence of the problem. If the behavior has been present for an extended period (months to years), then a medical cause is unlikely. If a medical cause were contributing to a licking behavior that has been present for several months, clinical signs suggestive of an ongoing or progressive disease process should have already developed or worsened.

Presumptive GI upset. If you suspect nausea but cannot identify its cause and are limited in the diagnostic tests the owners will allow, consider presumptive treatment for gastrointestinal upset. If a course of famotidine (0.5 to 1 mg/kg orally once or twice a day) alone or in combination with metronidazole (10 to 15 mg/kg orally b.i.d.)11 for seven to 10 days stops the licking behavior, then more extensive diagnostic tests could be readily justified to look for the cause of the gastrointestinal upset.

Canine cognitive dysfunction

Dogs with cognitive dysfunction may display a variety of repetitive behaviors. But if the excessive licking behavior is a result of cognitive dysfunction, then treatment will be different than it is in dogs without cognitive impairment.

If the patient is more than 11 years old, studies have shown that there is a good chance it is showing at least one sign of cognitive decline.12,13 Common signs of cognitive decline include confusion, changes in relationships with people and other pets in the household, changes in activity level, disrupted sleep-wake cycles, and decreased ability to learn or remember commands (e.g. a previously well-housetrained dog may begin eliminating in the house).13 Cognitive dysfunction is a diagnosis of exclusion, so if a patient is showing signs of cognitive impairment along with repetitive behaviors, then possible medical causes must be ruled out before you treat the behavior problems.

Treating cognitive dysfunction may help reduce the signs of repetitive behaviors. Treatment, which may include behavior and environmental modification and drug therapy, is described elsewhere.13

Appetitive behaviors

The excessive licking of surfaces can be purely an appetitive behavior in a dog that is not so severely polyphagic as to exhibit pica. For example, in a household with small children, many dogs learn to lick the floors around the areas where children eat to consume food particles left behind. A dog that is on a severely restricted diet may also learn to lick the floor where food may have fallen. Once dogs have learned that they may be able to acquire food in these areas, the behavior may appear obsessive when it is simply a learned appetitive behavior.

Treating this condition simply requires identifying and thoroughly cleaning all areas where food has been dropped and limiting the dog's access to these areas. Using child gates to keep dogs away from the areas where children eat is a good idea.

Attention-seeking behavior

Many dogs that begin licking surfaces for any reason learn that performing the behavior results in a response from the owner. Even if that response is punishment, it may be rewarding to a dog that desires attention. Once dogs learn that a certain behavior results in attention, they are likely to repeat the behavior.

Finding out whether the behavior occurs when no people are present is the best way to determine if attention seeking is an important factor contributing to the licking behavior. The ideal way to do this is by videotaping the dog when it is alone. A video camera can be aimed at the general area where the dog spends much of its time and left recording when the owner leaves. Dogs whose behavior demonstrates an observer effect (they demonstrate the behavior less or not at all when no people are around) are unlikely to be experiencing a true compulsive disorder.

Treatment for attention-seeking behaviors requires that the owner completely ignores the dog whenever it begins performing the behavior. Tell the owner not to speak to the dog or even make eye contact and to leave the room if possible. If an owner can do this consistently, the behavior will eventually stop; however, initially, there may be a dramatic increase in the behavior (called an extinction burst) as the dog attempts to get the attention it is used to.14 If owners want the behavior to eventually stop, they must ignore this behavior completely, no matter how annoying it may be.

DIAGNOSING ABNORMAL REPETITIVE BEHAVIOR

Once medical problems have been ruled out, the licking can be called an abnormal repetitive behavior. In the literature, behaviors such as these have been referred to as stereotypies, obsessive-compulsive disorders, and compulsive disorders. To clarify the terminology used here, a set of definitions for these and related terms are presented in Table 2. In clinical practice, it is probably easiest to think of the term stereotypy as a description of a behavior and compulsive disorder as a diagnostic term.

Table 2: Useful Definitions for Understanding Abnormal Repetitive Behaviors

Compulsive disorders in dogs are thought to initially be brought on by situations of anxiety, conflict, or frustration and then, over time, to be shown outside of the original context.2,15 No one has yet determined exactly how long it takes for a repetitive behavior to develop into a compulsive behavior, but it is probably not a brief period.

No set diagnostic criteria for compulsive disorders are available.15 The diagnosis is based on the history and presenting signs and is reached after medical conditions and other behavior disorders, such as displacement or redirected behaviors, have been ruled out or treated. In my experience, displacement behaviors and redirected behaviors occur much more frequently in companion dogs than compulsive disorders do. However, ultimately, recognizing that a dog is experiencing anxiety, conflict, or frustration in its environment is much more important than determining whether the behavior is a true compulsive disorder. Attempting to determine the source of the anxiety, conflict, or frustration is critical to developing an appropriate treatment plan as outlined below.

The behavior of a dog experiencing anxiety or conflict may include licking its nose and lips repeatedly, yawning, shaking its head, or pacing, in addition to the more obvious signs such as cowering with its head and tail tucked and attempting to hide. Anxiety may also be accompanied by increased heart and respiratory rates, salivation, and dilated pupils, although these signs may be difficult to differentiate from those shown by many animals anxious about being in the veterinary clinic.

Situations that may lead to anxiety, conflict, or frustration include insufficient stimulation, alterations in routine, inconsistency of owner interactions such as improper use of punishment, the addition or departure of family members including other pets, and intense or recurrent fear-provoking events.2 In addition, since temperament plays an important role in the development of anxiety-related behavior problems, veterinarians should learn to recognize the signs that a dog has a fearful or anxious temperament.

Keep in mind that multiple causal factors play a role in the development of many behavior problems, and anxiety-related and compulsive disorders are no different. Often, the situation or medical condition that elicits a problem is not be the same one that maintains it,2 making the collection of the behavior and medical history critical to an accurate diagnosis. For example, medical conditions that cause pain or discomfort may lead to anxiety, and the anxiety may lead to displacement behaviors that with time can become compulsive behaviors. Because of this, correcting a medical condition may not always result in an immediate change in a behavior; behavior modification and environmental management (see below) may still be needed to change the behavior.

TREATING ABNORMAL REPETITIVE BEHAVIOR

Once it has been determined that the licking is a primary behavior problem stemming from anxiety, conflict, or frustration, treatment should consist of a combination of behavior modification, environmental management, and pharmacologic intervention.10 Using only one of these three components decreases the likelihood of achieving long-term success. The goal of these treatments is to decrease the anxiety and conflict that might have led to the compulsive disorder.2,8

As part of treatment, remind the owner to ignore the dog every time it begins to perform the behavior. Even if it is not the primary cause, an owner inadvertently rewarding the dog for licking can contribute to the persistence of the behavior.

Environmental management

The primary aim of therapy is to provide the dog with an environment that is as free of anxiety and conflict as possible, is appropriately stimulating (allows for normal species-typical behaviors), and in which owner interactions are predictable and consistent.2,8 Whenever possible, the source of conflict should be identified and removed from the animal's environment. When the source of anxiety or conflict cannot be removed (e.g. a new baby or pet), then desensitization to the anxiety-inducing stimuli should be attempted. Desensitization procedures have been well-described elsewhere.16

If the dog is not being provided with adequate exercise, encourage the owner to find ways to increase the dog's exercise that fit with their lifestyles. Although this may simply mean longer walks, aerobic exercise, such as chasing a ball or participating in flyball or agility training, is ideal. Many owners need to be taught that leaving a dog in the yard all day does not guarantee that it is getting adequate exercise. Most dogs, especially those living in single-pet households, do not exercise themselves. They sleep most of the day and wait for their owners to come home and then attempt to initiate interactions with them.

Enriching the dog's environment with a variety of interactive objects,2 such as toys that move or make noise when the dog interacts with them or toys that dispense food (e.g. Kong or Busy Buddy [Premier], Buster Cube [Kruuse A/S]), gives the dog an opportunity to get some exercise while home alone. It also allows the dog to exhibit normal species-typical behaviors, such as chewing and exploring. Each dog's preferences may need to be explored to determine what type of objects will most appeal to it. The toys should be rotated regularly so that they continue to be new and interesting to the dog.

Behavior modification

All punishment should be stopped immediately. Since most pet owners do not use punishment appropriately (within 1 to 2 seconds every time the inappropriate behavior occurs, at the proper intensity), punishment can be an important source of conflict and anxiety for pets.2,8

Command-response-reward exercises. For the first two to four weeks of treatment, owner interactions should be limited to providing food, exercise, and other necessities as well as daily training sessions.15 These training sessions should be highly structured interactions in which the animal is asked to respond to a command that it already knows well, and when it responds, it is rewarded. Dogs should not be punished for failing to respond; they just do not get the reward. These sessions provide the owner with an appropriate way to interact with the dog. The predictability and consistency of these command-response-reward exercises can dramatically decrease a dog's anxiety.

Response substitution. If the owner learns to recognize the circumstances in which the dog is likely to perform the licking behavior, he or she can try a technique called counter-conditioning or response substitution.10 As the latter term suggests, the purpose of this training is to teach the dog to provide an alternative response instead of performing the unacceptable behavior. There are several ways owners can accomplish this, but it will take time, patience, and consistency to be successful.

Owners of smaller dogs can attach a long leash from their dogs to themselves as they move about the home. Ideally, the dogs should also be wearing head collars during this time. When an owner sees that the dog shows signs that it will begin licking, he or she should immediately but calmly distract the dog by pulling it to him or her or by giving the dog a command, such as come or sit. It is important that the owners only use a command that the dog knows well and is likely to respond to at that moment. For this reason, it may be necessary for the owner to practice the command-response-reward exercises as described above for a few weeks before beginning the counter-conditioning exercises.

Owners who feel uncomfortable tethering their dogs to themselves will need to try other methods of distracting their dogs when it appears they may start licking surfaces. Squeaky toys, whistles, shaker cans (a can filled with beans or coins), or other noise-making devices can be effective.2 Other alternatives are squirt water bottles, cans of compressed air, ultrasonic devices, or citronella sprays. It is important to make owners aware that the purpose of these devices is to interrupt a dog's behavior so an alternate behavior can be rewarded. Their purpose is not to decrease the likelihood of the recurrence of the behavior (as appropriately applied punishment would do), so it is critical that the distracting device does not cause any fear or anxiety. If the chosen device appears to increase a dog's anxiety or cause a fearful response, it should be stopped immediately, and a less-startling device should be tried. It should absolutely not be paired with the owner yelling or telling the dog, "No." Once the dog is successfully distracted and looking to the owner for a command, the owner should calmly give the dog a command and reward it for responding appropriately.

Initially, a dog should be rewarded every time it responds to a command, preferably with a valued item or food treat. After the dog responds to a command, the owner should attempt to engage the dog in other rewarding activities such as play.

Pharmacologic intervention

Pharmacologic treatment can be a useful adjunct to behavior modification and environmental management when treating any anxiety-related disorder. Drugs acting on the serotonergic system have been found effective in treating anxiety and both human obsessive-compulsive disorders7 and canine compulsive disorders.10

Clomipramine. Clomipramine, a tricyclic antidepressant with selective serotonergic properties, has anxiolytic as well as anticompulsive effects, so it is a possible drug choice for treating a dog that repetitively licks surfaces. Sedation and anorexia are the most commonly noted side effects,17 but nausea, regurgitation, or increased water consumption may also occur.18

The recommended dosage of clomipramine in dogs is 1 to 3 mg/kg given orally twice daily.18 Do not give clomipramine in conjunction with monoamine oxidase inhibitors, such as selegiline, which are commonly used to treat canine cognitive dysfunction. In addition, administering clomipramine for more than 112 days at 3 mg/kg every 12 hours has been shown to significantly decrease total thyroxine, free thyroxine, and 3,3',5'–tri-iodothyronine concentrations.18 Signs of clinical hypothyroidism were not reported at this dose. But being aware of these medication-related effects should help you avoid unnecessary treatment for hypothyroidism.18

Fluoxetine. Fluoxetine, a selective serotonin reuptake inhibitor, may also be useful in treating repetitive surface licking behavior. It has fewer effects on other neurotransmitters than do other antidepressants, such as the tricyclic antidepressants, so it may have fewer side effects.19 Similar to clomipramine, fluoxetine has been shown to be effective in treating canine compulsive disorders20 as well as other anxiety-related disorders in dogs and cats.19 In one study in dogs receiving fluoxetine, the adverse events were limited to lethargy and decreased appetite, and no side effects were severe enough to warrant discontinuing the medication.20

The recommended dosage for fluoxetine in dogs is 1 to 2 mg/kg administered orally once daily.19 Fluoxetine may affect blood glucose concentrations, so diabetic patients should be monitored carefully while receiving this medication.19 As with clomipramine, never give fluoxetine with monoamine oxidase inhibitors, and use caution when giving fluoxetine or clomipramine to patients with existing renal or liver failure.18,19

Duration of drug therapy. More information about the safe and appropriate use of the psychotropic drugs can be found in the text Veterinary Psychopharmacology. Remind clients that while some anxiety-related disorders might respond to pharmacologic intervention within a few days or weeks, compulsive disorders might respond much more slowly. An owner should be prepared to treat for a minimum of four to six weeks before deciding if improvement is noticeable.10 If the medication appears to be helping, continue treatment for at least one or two months after the cessation of the clinical signs and then gradually taper the dosage and stop the drug if signs do not reappear during dosage reduction.2 Some patients with compulsive disorders will always require medication to maintain remission, especially if the causal factors cannot be identified and changed.

CONCLUSION

A dog's excessive licking of surfaces is most likely a result of a medical condition leading to nausea or gastrointestinal distress. It may occasionally be a result of anxiety or conflict leading to displacement behaviors and eventually an actual compulsive disorder. An accurate diagnosis will require excellent history-taking skills and patience on the part of the clinician and dog owner. If the cause is determined to be primarily behavioral, treatment includes attention to the dog's environment and behavior modification in addition to pharmacologic therapy. Pharmacologic therapy is not as likely to be effective without behavior and environmental modification, and remission is likely when the drug is discontinued if causative factors have not been identified and changed.

Valarie V. Tynes, DVM, DACVB

P.O. Box 1040

Fort Worth, TX 76101

REFERENCES

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