Dominance aggression is one of the most frequent types of aggression in dogs. Diagnostic criteria for dominance aggression include the target of the attacks, the context in which aggression occurs and the dogs posture during the episodes. Dominant dogs behave aggressively towards family members, in competitive contexts and showing a dominant or offensive posture. However, dominance related aggression occurs together with other problems that make its diagnosis and treatment more difficult. These conditions are hypothyroidism, fear, impulsivity and the so-called rage syndrome.
Hypothyroidism is one of the organic conditions currently referred as a cause of aggressive behavior in dogs. Dogs affected by hypothyroidism related aggression can show other typical signs of thyroid deficiency, like lethargy, obesity, skin problems, etc. However, in some cases the only symptom is aggression itself. Therefore, the fact that the dog shows no other signs of hypothyroidism doesn't preclude a diagnosis of hypothyroidism related aggression.
Aggression related to thyroid deficiency can be manifested in different ways. In some cases, the dog shows an aggressive behavior not related to any definable contexts and that could even be directed towards inanimate objects. However, in others, aggression is pretty similar to the one observed in dominance aggression and hypothyroidism could be considered not as much as the primary cause but an aggravating factor. In such cases, the clinical history could be virtually indistinguishable from one of dominance aggression. Considering this fact, it seems reasonable to include a thyroid test as a part of the routine diagnostic protocol for dominance aggression in dogs.
The exact mechanism that links aggression and hypothyroidism is not completely understood. It has been suggested that hypothyroidism could lowers the threshold of aggression by decreasing the serotonin turnover in the central nervous system, as serotonin is one of the main neurotransmitters involved in the control of aggression.
A measure of T4 in conjunction with TSH levels is the test preferred by most endocrinologists.
A low level of T4 together with an increased TSH value leads to a diagnosis of hypothyroidism. Reference values for both parameters depend on each laboratory. If laboratory results are not conclusive, a treatment trial with l-thyroxine should be done.
Prognosis for hypothyroidism related aggression is generally good and a marked response to treatment is often observed. If hypothyroidism is concomitant to a problem of dominance aggression, treatment should also include the behavior modification techniques to correct this form of canine aggression. Anyhow, treatment of thyroid deficiency is based in the administration of l-thyroxine, with a recommended dose of 20 µg/Kg PO q12. The effects on behavior can be observed after a few weeks of drug treatment. The administration of l-thyroxine should be not discontinued.
When applied to canine aggression, the term impulsivity means a reduction or a complete lack of warning signals previous to an attack. Impulsive dominant dogs do not show typical warning signals, like growls or bared teeth. Thus, aggression becomes sudden and unpredictable. Impulsivity makes the dog more dangerous and complicates diagnosis, especially because it is difficult for the owners to link the occurrence of aggression episodes to specific situations. Also, impulsivity is one of the criteria to decide if pharmacological treatment should be used. Most behaviorists recommend the use of selective serotonin reuptake inhibitors (SSRI) to treat these dogs.
Although the underlying mechanism for impulsivity has not been completely elucidated, some studies correlate impulsivity with low levels of 5-HT. Some impulsive behaviors in human medicine have also been linked to low levels of this neurotransmitter. On the other hand, impulsivity could also be the result of an instrumental conditioning where the dog learns that warning signals are not useful then skip them.
A lot of dogs showing aggression in competitive situations do not display the typical offensive posture of dominance aggression. Instead, an ambivalent posture typical of fear aggression is showed during aggression episodes. There seem to be different reasons for that. First, hierarchic conflicts between dogs are quickly resolved and the resulting hierarchy tends to be very stable. However, in the domestic environment a quite different situation could be found. Owners sometimes behave toward the dog as dominant individuals whereas in other situations they adopt a submissive posture. This lack of consistency leads to a poor defined relationship between the dog and its owners. As a result, the dog shows at the same time signs of dominant and submissive behavior. Second, it has been suggested that some of these aggression problems are not related to dominance but to conflict or fear aggression. Aggressive behavior is explained as a defense behavior in front of and unpleasant situation. Anyhow, it is possible that even in this situation the dog shows some degree of dominant behavior. Consistently, these two theories are not mutually exclusive. In our opinion, this kind of aggression should be treated as a form of dominance related aggression where amitriptyline should be added as a first line drug.
Some clinical ethology textbooks describe the so-called rage syndrome that could be understood as a form of dominance related aggression. It seems to be a breed predisposition for this problem in the Welsh Springer Spaniel and the English Cocker Spaniel, especially in its golden coat. The problem can be manifested at a very early age. Aggression occurs in situations consistent with a diagnosis of dominance aggression and is very impulsive in nature. Frequently, the dog shows other typical signs of dominance aggression. Owners often describe a glazed look in the dog during the attacks. Sometimes the dog shows a fear posture during of shortly after the aggression episodes. Explanations for this kind of aggression differ from one author to the other. Some specialists consider the rage syndrome as a severe form of dominance aggression that can be manifested in response to very low intensity stimuli. Others suggest the syndrome is a form of psychomotor epilepsy. Finally, some authors refer to this problem as distimia which should be considered a problem with a complex etiology that should be distinguished from dominance aggression. Whatever the explanation, the clinical criteria adopted by our referral service is to understand the rage syndrome as a severe form of dominance aggression, whose treatment protocol include the use of fluoxetine. The rage syndrome has a very poor prognosis.
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