Curriculum · Musculoskeletal / Orthopedic / Rheumatology
Ankylosing spondylitis
What it is
Ankylosing spondylitis is one subset of the broader category of axial spondyloarthritis. It is an autoimmune process associated with the HLA-B27 gene that attacks the vertebral joints; collagen is destroyed and replaced with fibrin, ossification sets in, and the spine takes the bamboo shape. It belongs to the seronegative spondyloarthropathy group alongside psoriatic arthritis, enteropathic arthritis and reactive arthritis.
Causes and risk
It is associated with HLA-B27, and the two pages do not put the same frequency on it: one has it found in 74%-89% of patients with the disease, the other has more than 90% of patients positive for HLA-B27 and calls it a predisposing factor for the disease. Men are affected more than women and the peak age is 15-40 years. The typical picture drawn for the group is a young male with stiffness in the low back, thigh, hip or buttocks. The aetiology is put as primary, or associated with psoriasis or IBD. The sex ratio is given as 5 males to 4 females, the male disease usually the severe one, and it presents in the 20s with a strong association with HLA-B27. Ankylosing spondylitis is also named among the extraintestinal manifestations of ulcerative colitis, beside sacroiliitis, osteoarthritis, primary sclerosing cholangitis, erythema nodosum, pyoderma gangrenosum and uveitis.