Preliminary evaluation of beta-endorphin alone and in combination with adrenocorticotropic hormone for the diagnosis of pituitary pars intermedia dysfunction in equids.

BACKGROUND: Limited published data exist regarding the diagnostic utility of beta-endorphin (β-END) for pituitary pars intermedia dysfunction (PPID), either compared with or in combination with adrenocorticotropic hormone (ACTH). HYPOTHESIS/OBJECTIVES: To evaluate β-END as a potential diagnostic test for PPID in comparison with ACTH and to explore the diagnostic performance of combined tests. ANIMALS: Ninety-eight equids aged 19-32 years, owned by the foundation "Stiftung für das Pferd," were included. METHODS: A cross-sectional study was conducted in January 2025. Haircoat abnormalities were scored as absent, mild, or pronounced, and plasma β-END and ACTH concentrations were measured. Horses were classified based on haircoat abnormalities, with pronounced haircoat abnormalities defining the PPID group (n = 39) and absence of haircoat abnormalities defining the control group (n = 59). Receiver-operating characteristic (ROC) analyses were performed for individual and combined diagnostic tests. Previously established ACTH cut-offs were combined with study-derived maximum Youden-Index cut-offs. RESULTS: Beta-endorphin showed an area under the ROC curve (AUROC) of 0.88 for PPID diagnosis, with a sensitivity of 76.9% and specificity of 93.2%. Corresponding AUROCs, sensitivities, and specificities were 0.87, 71.8%, and 88.1% for ACTH measured by chemiluminescent assay (CLA), and 0.83, 79.5%, and 69.5% for ACTH measured by immunofluorescent assay (IFA). Combining β-END at 115 pg/mL with ACTH (CLA) at 24.3 pg/mL yielded 88% sensitivity and 89% specificity. CONCLUSIONS AND CLINICAL IMPORTANCE: These preliminary findings support further evaluation of β-END as an adjunct diagnostic test for PPID.