Is axial spondyloarthritis (axSpA) one disease or does it comprise multiple types? If the latter, how do we define those types-through clinical or imaging features, HLA-B27 status, or by other immunologic features? Data comparing disease outcomes for individuals with nonradiographic vs radiographic axSpA, or for male vs female patients, demonstrate distinctions. So then, how should we define endotypes? Endotypes are known as the subtype of a health condition defined by a functional or pathophysiologic function. Here, we review the endotypes used for defining rheumatoid arthritis, asthma, and psoriatic arthritis. Taking the lessons learned from these diseases, we discuss how they can be applied to defining endotypes in axSpA. A key unmet need for axSpA is access to affected tissues for interrogation of their pathologic mechanisms, from which tissue-specific endotypes can be defined. These tissue-based features should be combined with clinical data and imaging to inform classification criteria in the future.

中文翻译：

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中轴型脊柱关节炎是否存在疾病内型，我们如何定义它们？


中轴型脊柱关节炎 （axSpA） 是一种疾病还是包含多种类型？如果是后者，我们如何通过临床或影像学特征、HLA-B27 状态或其他免疫学特征来定义这些类型？比较非影像学 axSpA 个体与影像学 axSpA 个体或男性与女性患者的疾病结局的数据表明存在差异。那么，我们应该如何定义内型呢？内型被称为由功能或病理生理功能定义的健康状况的亚型。在这里，我们回顾了用于定义类风湿性关节炎、哮喘和银屑病关节炎的内型。从这些疾病中吸取教训，我们讨论了如何将它们应用于定义 axSpA 中的内型。axSpA 的一个关键未满足需求是获得受影响的组织以询问其病理机制，从中可以定义组织特异性内型。这些基于组织的特征应与临床数据和影像学检查相结合，以便为将来的分类标准提供信息。