Canine atypical hyperadrenocorticism associated with hypothyroidism

Hyperadrenocorticism (HAC) is one of the most common endocrinopathies in dogs, caused by excessive synthesis of cortisol. Atypical or occult HAC is a syndrome characterized by the presentation of clinical, biochemical, and imaging alterations compatible with hypercortisolism, but normal results in endocrine tests that are conventionally used for HAC diagnosis. However, these patients present high serum concentrations of precursors or other corticoadrenal hormones. The present study describes the case of an 8 years old female canine, Bichón Frisé, epileptic and treated with phenobarbital, presenting clinical signs associated with HAC, in which the low-dose dexamethasone suppression test and stimulation with ACTH resulted within normal values. The measurement of adrenal steroids, after ACTH stimulation, showed abnormal elevation of estrogen and progesterone, the latter persisting after the patient was spayed. Treatment with trilostane allowed the reduction of progesterone levels and the partial resolution of clinical signs. However, full clinical recovery was only achieved after the diagnosis and treatment of concomitant hypothyroidism. The challenge that represent the diagnosis of atypical HAC highlights the importance of performing and having availability of panels that include measurement of adrenal steroid hormones other than cortisol, as well as considering the occurrence of other concomitant endocrine metabolic diseases