Background: Successful treatment of cats with hypersomatotropism by transsphenoidal hypophysectomy is described in small numbers of cats. Objectives: To describe the endocrine profile, survival, and remission rates of hypersomatotropism and diabetes mellitus in a cohort of cats with hypersomatotropism that underwent hypophysectomy between 2008 and 2020. Animals: Twenty-five client-owned cats with spontaneous hypersomatotropism. Methods: Retrospective study. Diagnosis of hypersomatotropism was based on clinical signs, plasma insulin-like growth factor-1 (IGF-1) concentration, and imaging of the pituitary gland. Growth hormone (GH) and IGF-1 concentrations were measured repeatedly after surgery. Survival times were calculated based on follow-up information from owners and referring veterinarians. Results: Median postoperative hospital stay was 7 days (range, 3-18 days). One cat died within 4 weeks of surgery. Median plasma GH concentration decreased significantly from 51.0 ng/mL (range, 5.0-101.0 ng/mL) before surgery to 3.8 ng/mL (range, 0.6-13.0 ng/mL) at 5 hours after surgery. Remission of hypersomatotropism, defined as normalization of plasma IGF-1 concentration, occurred in 23/24 cats (median, 34 ng/mL; range, 14-240 ng/mL) and 22/24 cats entered diabetic remission. Median survival time was 1347 days (95% confidence interval, 900-1794 days; range, 11-3180 days) and the overall 1-, 2-, and 3-year all-cause survival rates were 76%, 76%, and 52%, respectively. Conclusions and Clinical Importance: This study shows the beneficial outcome of hypophysectomy in cats with hypersomatotropism, marked by low death rate and a high percentage of diabetic remission and definitive cure.

Background: The adrenocorticotropic hormone (ACTH) stimulation test is used to evaluate trilostane treatment in dogs with hypercortisolism. Hypothesis: The urinary corticoid : creatinine ratio (UCCR) is a good alternative to the ACTH stimulation test to determine optimal trilostane dose. Animals: Eighteen dogs with pituitary-dependent hypercortisolism. Methods: In this prospective study, the dose of trilostane was judged to be optimal on the basis of resolution of clinical signs of hypercortisolism and results of an ACTH stimulation test. The owners collected urine for determination of UCCR at 2-week intervals for at least 8 weeks after achieving the optimal trilostane dose. Results: The UCCRs were significantly higher before treatment (11.5–202.0 × 10−6; median, 42.0 × 10−6) than at rechecks 2 months after optimal dosing, but they did not decrease below the upper limit of the reference range in the majority of dogs. The UCCRs of 11 dogs that initially were dosed insufficiently (range, 7.5–79.0 × 10−6; median, 31.0 × 10−6) did not differ significantly from UCCRs when the dosage was optimal (8.2–72.0 × 10−6; median, 33.0 × 10−6). Post-ACTH cortisol concentrations did not correlate significantly with UCCRs at rechecks during trilostane treatment. Long-term follow-up indicated that the decrease in UCCR below the upper limit of the reference was associated with hypocortisolism. Conclusion and Clinical Importance: The UCCR cannot be used as an alternative to the ACTH stimulation test to determine the optimal dose of trilostane, but might be helpful in detecting dogs at risk for developing hypocortisolism during trilostane treatment.