Frequency of low-dose dexamethasone suppression test (LDDST) response patterns and their correlation with clinicopathologic signs in dogs suspected of having Cushing's syndrome: A retrospective study

A retrospective cross-sectional study was conducted to assess the frequency of low-dose dexamethasone suppression test (LDDST) patterns in canine patients that had clinicopathologic signs consistent with Cushing's syndrome (CS). Medical records for patients of interest (N = 128) were reviewed between January 2014 and December 2020 to analyse and classify LDDST results based upon the following patterns: lack of suppression, partial suppression, complete suppression, escape, or inverse. Complete suppression, lack of suppression, partial suppression, escape, and inverse patterns were identified in 39.1%, 31.2%, 14.1%, 10.1% and 5.5% of cases respectively. LDDST results were also evaluated with respect to clinical signs, serum alkaline phosphatase (ALP) activity, urine specific gravity (USG) and adrenal ultrasonographic findings. There was no association between LDDST patterns and clinical signs (p = 0.11), increased ALP (p = 0.32), USG (p = 0.33) or adrenal ultrasonographic findings (p = 0.19). In all dogs that demonstrated complete suppression or an inverse pattern, CS was excluded by the attending clinician. The diagnosis of CS was also excluded without further exploration in 23.1%, 7.5% and 5.6% of dogs that demonstrated an escape pattern, lack of suppression and partial suppression pattern, respectively. These results suggest that the clinical significance of LDDST patterns, particularly escape and inverse patterns, are misunderstood by some clinicians, leading them to prematurely exclude the diagnosis of CS.