Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA.
Equine Studies, Department of Science & Health, Asbury University, One Macklem Drive, Wilmore, KY 40390, USA.
Vet J. 2023 Oct-Dec;300-302:106035. doi: 10.1016/j.tvjl.2023.106035. Epub 2023 Oct 5.
Pituitary pars intermedia dysfunction (PPID) is an age-related neurodegenerative disorder, affecting >20 % of older horses. There is a need for improved endocrine tests for early disease detection, and the thyrotropin-releasing hormone (TRH) stimulation test has been recommended for diagnosis of early or mild cases. However, it is currently not recommended for year-round use due to marked seasonal variability. The aims of this cohort study were to evaluate effects of month and season on adrenocorticotropic hormone (ACTH) responses to TRH stimulation and to derive monthly cut-offs for PPID diagnosis. Sixty-three horses were assigned to control (n = 17), subclinical PPID (n = 21) and clinical PPID (n = 25) groups, based on a composite reference standard that combined clinical history and examination findings with endocrine test results. TRH stimulation tests were performed monthly for a 12-month period. Circannual changes were evaluated with one- and two-way repeated-measures analysis of variance and receiver operating characteristic curve analysis was used to derive cut-off values for basal and TRH-stimulated ACTH. TRH-stimulated ACTH concentrations were lowest in February-May and highest in August-October. Specificity of both basal and 30 min post-TRH ACTH was generally higher than sensitivity, and TRH stimulation had improved diagnostic accuracy compared to basal ACTH, although its sensitivity was not significantly greater year-round. TRH stimulation tests yielded considerably more positive results than basal ACTH in the subclinical group, but few additional positive results in clinical PPID cases. There were large differences between cut-offs that maximised sensitivity or specificity for TRH-stimulated ACTH, highlighting the importance of considering clinical presentation alongside test results in diagnostic decision-making.
垂体中间叶功能减退症（PPID）是一种与年龄相关的神经退行性疾病，影响超过 20%的老年马匹。需要改进内分泌测试以早期发现疾病，促甲状腺素释放激素（TRH）刺激试验已被推荐用于早期或轻度病例的诊断。然而，由于季节性变化明显，目前不建议全年使用。本队列研究的目的是评估月份和季节对 TRH 刺激后促肾上腺皮质激素（ACTH）反应的影响，并得出用于诊断 PPID 的每月截止值。根据综合参考标准，将 63 匹马分为对照组（n=17）、亚临床 PPID 组（n=21）和临床 PPID 组（n=25）。综合参考标准结合了临床病史和检查结果以及内分泌测试结果。在 12 个月的时间内每月进行 TRH 刺激试验。使用单因素和双因素重复测量方差分析评估年周期变化，使用接收者操作特征曲线分析得出基础和 TRH 刺激后 ACTH 的截止值。TRH 刺激后 ACTH 浓度在 2 月至 5 月最低，8 月至 10 月最高。基础和 30 分钟后 TRH ACTH 的特异性通常高于敏感性，TRH 刺激与基础 ACTH 相比，诊断准确性有所提高，尽管其敏感性在全年并未显著提高。TRH 刺激试验在亚临床组中产生了比基础 ACTH 更多的阳性结果，但在临床 PPID 病例中，阳性结果增加很少。为了最大化 TRH 刺激后 ACTH 的敏感性或特异性而得出的截止值存在很大差异，这突出了在诊断决策中，除了测试结果外，还应考虑临床表现的重要性。
