Abstract：
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.
摘要：
垂体间层功能障碍（PPID）是一种与年龄相关的神经退行性疾病，影响>20％的老马。有必要改进内分泌测试，以进行早期疾病检测，促甲状腺激素释放激素（TRH）刺激试验已被推荐用于早期或轻度病例的诊断。然而,由于明显的季节性变化，目前不建议全年使用。这项队列研究的目的是评估月份和季节对促肾上腺皮质激素（ACTH）对TRH刺激的反应的影响，并得出PPID诊断的每月截止值。63匹马被分配到对照（n=17），亚临床PPID（n=21）和临床PPID（n=25）组，基于将临床病史和检查结果与内分泌检查结果相结合的复合参考标准。TRH刺激试验每月进行12个月。通过单向和双向重复测量方差分析评估了每年的变化，并使用受试者工作特征曲线分析得出了基础和TRH刺激的ACTH的临界值。TRH刺激的ACTH浓度在2月至5月最低，在8月至10月最高。基础和30min后TRHACTH的特异性普遍高于敏感性，与基础ACTH相比，TRH刺激提高了诊断准确性，尽管其敏感性全年没有显著提高.在亚临床组中，TRH刺激试验比基础ACTH产生的阳性结果高得多。但在临床PPID病例中几乎没有其他阳性结果。对TRH刺激的ACTH的敏感性或特异性最大化的截止值之间存在很大差异，强调在诊断决策中考虑临床表现和检测结果的重要性。
