[Diagnosis and early diagnosis of ankylosing spondylitis]

Ankylosing spondylitis (AS) is often diagnosed not before 5-10 years after onset of clinical symptoms. The main reason for this delay is the late appearance of unequivocal radiographic sacroiliitis which is a prerequisite for making the diagnosis. It is important to realize that both the early stage without radiographic sacroiliitis and the late stage with radiographic sacroiliitis are part of the same disease and, therefore, should be considered as a disease continuum. The term axial spondyloarthritis (SpA) appears appropriate to describe this disease continuum. Diagnosing axial SpA without radiographic sacroiliitis, however, is difficult and associated with diagnostic uncertainties since there are no diagnostic criteria available. Considering all SpA features which are relevant for the diagnosis of axial SpA (with and without radiographic sacroiliitis), we have recently proposed a diagnostic algorithm based on calculations using Bayes' theorem to be applied in individual patients. This diagnostic algorithm enables the physician to diagnose or to exclude axial SpA with a high degree of confidence. An early and reliable diagnosis is relevant to both the patient and the physician since an early diagnosis allows the best therapy to be introduced and consequently maintained.