Spondyloarthritis refers to a group of inflammatory diseases characterized by spinal & joint oligoarthritis, enthesitis, and sometimes mucocutaneous, ocular and/or cardiac manifestations.
Ankylosing spondylitis is a prototype of spondyloarthritis, particularly of the axial form.
Diagnosis of ankylosing spondylitis is definite if any of the radiological criterion (grade≥2 bilateral sacroiliitis or grade ≥3 unilateral sacroiliitis) is associated with at least one of the clinical criterion (low back pain & stiffness for >3 months that improves with exercise but not relieved by rest, limitation of motion of the lumbar spine in the sagittal and frontal planes, limitation of chest expansion relative to normal values correlated for age and gender.