E20 - Pituitary Histomorphometry Correlation with Adrenocorticotrophin Response to Thyrotropin-releasing Hormone in Pituitary Pars Intermedia Dysfunction Diagnosis
Background: The thyrotrophin-releasing hormone (TRH) stimulation test is widely recommended by equine endocrinologists for the clinical diagnosis of pituitary pars intermedia dysfunction (PPID); however, the correlation between the response of adrenocorticotropic hormone (ACTH) in TRH stimulation test and pituitary histomorphometry is still unknow. Hypothesis/Objective – This study is to investigate the correlation between the pituitary histomorphometry and the ACTH concentrations after a TRH stimulation test. Animals: Fourteen horses ≥13 years of age, including 9 cases presenting typical PPID signs such as hypertrichosis, delayed shedding, and muscle atrophy, were euthanized in spring and summer for reasons unrelated to this study.
Methods: In all horses, 1 mg TRH was administered intravenously and ACTH concentrations determined 30 min later. After euthanasia, each pituitary gland was collected and hematoxylin-eosin stained slides were assessed by a board-certified pathologist blinded to the clinical information using a previously published grading system. Horses were divided into five groups by pituitary histology and one-way analyzes of variance (ANOVA) used to determine the associations between histological grade and post-TRH ACTH concentrations with of p < 0.05 considered significant.
Results: There was a significant histology group effect (P = 0.04) on post-TRH ACTH concentrations with higher histology grades having higher post-TRH ACTH concentrations. Conclusions and clinical importance: This study supports the use of the TRH stimulation test for the diagnosis of PPID as it correlates with pituitary histomorphometry. The recruitment of additional cases will allow the determination of more precise diagnostic cut-offs for the TRH stimulation test.
