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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

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., El hiperadrenocorticismo (HAC) es una de las endocrinopatías más frecuentes en caninos, producida por la síntesis excesiva de cortisol. El HAC atípico u oculto es un síndrome caracterizado por la presentación de alteraciones clínicas, bioquímicas e imagenológicas compatibles con hipercortisolismo, pero con resultados normales en las pruebas endocrinológicas utilizadas convencionalmente para diagnóstico de HAC. Sin embargo, estos pacientes presentan elevada concentración sérica de precursores u otras hormonas corticoadrenales. El presente estudio describe el caso de una canina hembra, Bichón Frisé de 8 años de edad, epiléptica y tratada con fenobarbital, presentando signos clínicos asociados a HAC, en la que el test de supresión con dexametasona a dosis bajas y de estimulación con ACTH arrojaron valores normales. La medición de esteroides adrenales, post estimulación con ACTH, mostró elevación anormal de estrógenos y progesterona, persistiendo esta última después de que la paciente fuera esterilizada. El tratamiento con trilostano permitió la disminución de los niveles de progesterona y la resolución parcial de los signos clínicos. Sin embargo, la recuperación clínica en su totalidad sólo se obtuvo después del diagnóstico y tratamiento del hipotiroidismo concomıtante. El desafío que representa el diagnóstico del HAC atípico resalta la importancia de realizar y disponer de paneles que incluyan medición de hormonas esteroideas adrenales diferentes al cortisol, además de considerar la ocurrencia de otras enfermedades endocrinas metabólicas concomitantes.