New Paradigms in the Diagnosis and Classification of the Spondylarthritis Nuevos paradigmas en el diagnóstico y la clasificación de las espondiloartritis

Important advances in the understanding of spondyloarthritis (SAs) have been made in the area of classification criteria1 and have significantly improved the approach to these diseases and the better identification of patients in early stages of the disease.2 Conceptually the term spondyloarthritis (SA) continues to represent a heterogeneous group of interrelated diseases3 called ‘spondyloarthritis’ (SA), although often used in the plural form, “spondyloarthritidies (SA)”, accentuating the sense of group, rather than a disease with different clinical presentations.4 In the medical sciences in general and in rheumatology in particular, systems of diagnostic criteria or classification are used interchangeably for research and for clinical practice. However, the differences between them are substantial and must be known before application. The diagnostic criteria should be applied to individual patients and should be especially sensitive (high sensitivity) to allow identification of patients with the disease even during the early stages. This depends on the prevalence of the disease. In contrast, the purpose of the classification criteria is to differentiate patients with a specific disease from patients with other illness or individuals from the general population, and are used in epidemiological research to create homogeneous groups of patients. These criteria should have high specificity and be applied to patients’ already diagnosed. Their qualities are not dependent on the prevalence and should not be applied “automatically” for diagnosis, especially in populations where the prevalence is low,5 as in general practices, where the prevalence of these is low and high for low back pain of mechanical origin. In the field of SA, two systems of criteria were developed almost simultaneously, the Amor6 and the European Group for the Study of spondylarthopathies criteria (EGSS),7 which have been very useful thanks to their good quality in terms of sensitivity (90.8% Amor and83.5%EGSS) and specificity (96.2%Amor and95.2%EGSS).However, the introduction of diagnostic imaging, especially MRI, which can detect early sacroiliitis, the efficacy of biological drugs in early stages of the disease8 and the need to recognize patients at increasingly early stages evidenced the shortcomings of these criteria for