Occult ACTH-dependent hyperadrenocorticism (HAC) in dogs is infrequent and may lead to a difficult diagnosis, since clinicians are faced with clinical signs of HAC, but no alterations on cortisol are observed to confirm the diagnosis.

We report a 12-year-old Shih Tzu spayed female dog who presented with polyuria, polydipsia, dyspnea, obesity, muscular weakness, exercise intolerance, and slightly pendulous abdomen. Laboratory findings included thrombocytosis, elevated serum concentrations of ALP and ALT associated with a low specific urinary gravity, but a normal serum cortisol concentration on low dose of dexamethasone suppression test (LDDST) and ACTH stimulation tests.

B-mode ultrasound abdominal examination was performed, revealing adrenal glands with normal form and size. In order to further evaluate adrenal tissue, ARFI elastography was held. The left adrenal gland (LA) presented a hypoechoic portion on caudal pole (Pcd) in relation to the cranial pole (Pcr).

The mean shear velocity value for LAPcd was 3.13 m/s, whilst LAPcr was 1.82 m/s, right adrenal gland (RA) Pcr was 1.99 m/s, and RAPcd was 1.5 m/s. This finding on LAPcd by ARFI has prompted the clinician to measure 17-OH-progesterone (17-OHP) and other sex hormones after ACTHST. Post-ACTH serum 17-OHP [4.06 ng/mL (0.40–1.62 ng/mL)] and androstenedione concentrations [6.01 ng/mL; (0.27–3.97 ng/mL)] were moderately elevated, while basal and post-ACTH serum concentration of aldosterone, cortisol, estradiol, progesterone, and testosterone were within reference ranges. These results show that ARFI elastography may provide important information in study of adrenals and may help in the diagnosis of occult hyperadrenocorticism (acknowledgement to FAPESP for financial support).