Causes of pain in patients with axial spondyloarthritis.

Back pain, most frequently of the inflammatory type, is the leading symptom in patients with axial spondyloarthritis (axSpA). Back pain in these patients is usually either due to axial inflammation or structural changes based on new bone formation. However, there are other possible causes of pain in these patients. There is, for example, a strongly increased risk of vertebral fractures, and, especially in patients with longstanding disease, degenerative spinal changes may play an additional role as a cause of pain. Rarely, but rather specifically, patients with ankylosing spondylitis may develop subarachnoidal cysts that often cause neurologic symptoms, in extreme cases a cauda equina syndrome. It is therefore mandatory to always carefully evaluate the origin of back pain in these patients and to consider all possible differential diagnoses. The correct diagnosis is of major importance because treatments may differ considerably. In the monitoring of patients with axSpA it is especially important to consider that pain may have a different origin and it is crucial to notice changes in the nature of the reported back pain. Accordingly, the recently updated Assessment of Spondyloarthritis international Society (ASAS)/European League Against Rheumatism (EULAR) and the treat-to-target recommendations both define improvement of symptoms, a reduction of pain and abrogation of inflammation as important targets in axSpA that can be achieved by pharmacological and nonpharmacological treatments, in rare cases including surgical methods.