The most common early symptoms of ankylosing spondylitis include:
Pain and stiffness. Constant pain and stiffness in the low back, buttocks, and hips that continue for more than three months. Spondylitis often starts around the sacroiliac joints, where the sacrum (the lowest major part of the spine) joins the ilium bone of the pelvis in the lower back region.
Bony fusion. Ankylosing spondylitis can cause an overgrowth of the bones, which may lead to abnormal joining of bones, called "bony fusion." Fusion affecting bones of the neck, back, or hips may impair a person's ability to perform routine activities. Fusion of the ribs to the spine or breastbone may limit a person's ability to expand his or her chest when taking a deep breath.
Pain in ligaments and tendons. Spondylitis also may affect some of the ligaments and tendons that attach to bones. Tendonitis (inflammation of the tendon) may cause pain and stiffness in the area behind or beneath the heel, such as the Achilles tendon at the back of the ankle.
There is no consensus on the diagnosis of AS, but the 1984 Modified New York classification criteria has been generally accepted for both research and clinical purposes. It requires at least 1 clinical manifestation and at least 1 radiographic parameter. Clinical manifestations include ≥ 3 months of inflammatory back pain that improves with exercise and exacerbated by rest, limitation of lumbar motion in both frontal and sagittal planes, and limitation of chest expansion compared to the normative population. Radiographic parameters include ≥ grade 2 sacroiliitis bilaterally or grade 3 or 4 sacroiliitis unilaterally.
Correct diagnosis requires a physician to assess the patient’s medical history and do a physical exam. The doctor also may order imaging tests or blood tests. You may need an X-ray of the sacroiliac joints, a pair of joints in the pelvis. X-ray changes of the sacroiliac joints, known as sacroiliitis, are a key sign of spondyloarthritis. If X-rays do not show enough changes, but the symptoms are highly suspicious, your doctor might order magnetic resonance imaging, or MRI, which shows these joints better and can pick up early involvement before an X-ray can.
Among the blood tests you may need is a test for the HLA-B27 gene. However, having this gene does not mean spondyloarthritis will always develop. Some people have the HLA-B27 gene but do not have arthritis and never develop arthritis. In the end, the diagnosis relies on the doctor’s judgment.