Retrospective study on hypersensitivity-hyperactivity syndrome in dogs: long-term outcome of high dose fluoxetine treatment and proposal of a clinical score

Abstract

In the French veterinary psychiatry model, the canine version of attention deficit hyperactivity disorder is called hypersensitivity-hyperactivity syndrome (HSHA) and it includes two stages, depending on the symptom severity. Since methylphenidate is not authorized for veterinary use in France, HSHA dogs are commonly treated with 2 to 4 mg/kg fluoxetine associated with behavioural modifications. Thus, the aim of this study was to analyze the long-term outcome of this global approach. Twenty-four dogs diagnosed with HSHA were included. For each dog, 42 descriptive data were analyzed. Primary reasons for consulting were variable if the dogs had an additionnal behavioural diagnosis (i.e. 33% of the dogs): complaints were linked to the comorbid diagnosis (e.g. bite on strangers, people phobia), whereas they were linked to autocontrol deficiency for the dogs diagnosed with HSHA only (e.g. destructive, mouth, jumps on people).

HSHA affection deeply alters the dog-human bond, as severe cases often lead owners to think about euthanasia or rehoming (12% for stage 1, but 83% for stage 2).

Neither the possibility to have access to a garden nor the quantity of daily exercise were linked to HSHA stages (respectively, Fisher’s exact test, p=0.69, and Kruskal-Wallis, p=0.88).

Eighty-three percent of the dogs attended training classes before consulting, with no noticeable improvement (mean training improvement score 1.7/10). In addition, training seemed even less efficient on severe cases, i.e. stage 2 dogs (Kruskall-Wallis, p<0.03).

After two months of high dose fluoxetine (2 to 4 mg/kg), the average score of improvement given by owners was 7.2/10 compared to 0/10 at start. No long-term adverse effect was reported.

A HSHA clinical score (0 to 5 scale) was built to better categorize the dogs and to conduct the follow-up. The HSHA clinical score was correlated to fluoxetine dose (Pearson correlation, p<0.01) and duration (Pearson correlation, p<0.05). A successful weaning from treatment was possible for 54% of the dogs.

These results suggest that HSHA spectrum can range from mild clinical signs to widely pervasive and invalidating ones. Starting the treatment as early as possible seems determinant for the welfare of the dog and for the dog-owner relationship, but doesn’t allow a shorter treatment (Kruskall-Wallis, p=0.84) or more chances for a weaning (Fisher’s exact test, p=0.88). However, high dose fluoxetine associated with behavioural modifications appear to be useful and well tolerated to treat this complex syndrome.