Natural course of Axial Spondyloarthritis
Although the course is variable, the first 10 years predict the subsequent course of the disease. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) or Ankylosing Spondylitis Disease Activity Score (disease activity), Bath Ankylosing Spondylitis Metrology Index (spinal mobility score), and Bath Ankylosing Spondylitis Functional Index (functional index) are standardized instruments used by some clinicians to measure disease progression and response to therapy. Early factors that predict a poor prognosis include early hip joint involvement, ESR >30 mm/hour or persistently high CRP, poor response to NSAID therapy, and early development of syndesmophytes. Extraarticular manifestations such as uveitis, cardiovascular involvement, and pulmonary fibrosis portend a poor outcome. Patients with mild axSpA have a normal life expectancy and will maintain their ability to work. However, patients with poor prognostic signs have a three times increased risk of withdrawing from the workforce and one and a half times increased risk of dying. Causes of death include cardiovascular disease, infections, malignancy, and (rarely) spinal fractures.