Thyroid Dysfunction as a Cause of Aggression in Dogs and Cats

In human medicine, behavioral and psychological changes associated with thyroid dysfunction were noted in the nineteenth century. The behavioral abnormalities seen in the hyperthyroid cat have been well described in the literature, and mimic closely the restlessness, insomnia and irritability or aggression described in humans with thyrotoxicosis. Approximately 80% of hyperthyroid cats are hyperactive, while 10-25% are reported to be aggressive. Cats, as well as people, may experience the rarer manifestation of apathetic thyrotoxicosis, characterized by lethargy and depression. This is seen in approximately 10% of feline cases. Hyperthyroid cats are rarely presented to the veterinarian for behavioral signs, Perhaps because aggression is primarily wen when the cat is restrained, we as a profession are more likely to experience this aspect of the disease than the cats' owners, Treating the underlying thyroid problem generally resolves the behavioral problems however, and because onset is often insidious, it is only after the endocrine imbalance has been addressed that the owners appreciate the deterioration in their animal's behavior