Evaluation of clinical, ultrasonographic, and clinicopathological findings in dogs with pituitary-dependent hypercortisolism and poor trilostane response.

Elevated baseline ALT, eACTH, pre-ACTH cortisol, and bilateral adrenomegaly predict poor trilostane response in PDH dogs.

This retrospective cohort study evaluated clinical, clinicopathological, ultrasonographic, and endocrine variables at diagnosis to identify predictors of poor trilostane response in 23 dogs with pituitary-dependent hypercortisolism (PDH). Dogs were classified as good responders (GRs, n=15) or nonresponders (NRs, n=8) based on clinical outcomes at 4–8 months post-treatment initiation. At diagnosis, NRs demonstrated significantly higher alanine aminotransferase (ALT), endogenous ACTH (eACTH), and pre-ACTH stimulation cortisol concentrations compared to GRs. Bilateral adrenomegaly on ultrasound was universally present in NRs (8/8) versus only 60% of GRs (9/15). During follow-up, NRs required significantly more rechecks and substantially higher trilostane doses (median 3.25 vs 1.22 mg/kg q12h). After false discovery rate correction, elevated ALT, elevated eACTH, presence of alopecia, and bilateral adrenomegaly remained statistically significant predictors of poor response. Notably, all GRs achieved complete clinical resolution within 4 months of treatment initiation, suggesting that failure to respond by this timepoint warrants early therapeutic reassessment—including consideration of alternative diagnoses or treatment modalities such as adrenalectomy or radiation therapy. Limitations include small sample size, retrospective design, and inherent selection bias. Nevertheless, these findings provide clinically actionable baseline variables that may help practitioners stratify PDH patients by likelihood of trilostane response and set realistic treatment expectations prior to initiating therapy.

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