Ankylosing spondylitis (AS) is a chronic inflammatory disease that mainly affects the sacroiliac joints, spinal prominences, paraspinal soft tissues and peripheral joints, and may be accompanied by extra-articular manifestations, and in severe cases, spinal deformity and ankylosis may occur.
The prevalence of AS is reported differently in different countries, and the preliminary survey of the prevalence in China is about 0.3%. The ratio of men to women is about 2 to 3:1, and the onset of the disease is slow and mild in women. The cause of AS is not known. The cause of AS is unknown, but it has been shown that the onset of AS is closely related to human cellular antigen (HLA)~B27, and there is a clear tendency of family aggregation.
1. Clinical manifestations
The onset of the disease is insidious. Patients gradually develop pain and/or morning stiffness in the low back or sacroiliac region, wake up with pain in the middle of the night, have difficulty turning over, and morning stiffness in the low back is obvious when getting up in the morning or after sitting for a long time, but is relieved after activity. Coughing, sneezing, and sudden twisting of the lumbar pain can be aggravated. In the early stage of the disease, the hip pain is mostly intermittent or alternating on one side, and after a few months, the pain is mostly bilateral and continuous.
Hip and peripheral joint lesions occur in 24% to 75% of AS patients at the beginning or during the course of the disease, with the knee, ankle and shoulder joints predominating, and the elbow and small joints of the hand and foot occasionally being involved. Arthritis or arthralgia in the hip and knee, as well as in other joints, occurs early in the course of the disease. The hip joint is involved in 38% to 66% of cases, showing local pain, restricted movement, flexion contracture and joint ankylosis, most of which are bilateral, and 94% of the hip symptoms start within the first 5 years after the onset of the disease.
2.Diagnostic points
The most common and characteristic early complaints of AS are morning stiffness and pain in the lower back. 2009 International AS Assessment Task Force (ASAS) Inflammatory Back Pain Experts recommended the following criteria for the diagnosis of inflammatory back pain.
At least 4 of the following 5 are met.
① Age of onset < 40 years.
② insidious onset.
(iii) symptoms improve with activity.
④ aggravation at rest.
⑤ nocturnal pain (improves after waking up).
The diagnosis of AS inflammatory back pain was made when 4 of the above 5 indicators were met. Its sensitivity is 79.6% and specificity is 72.4%.
3.Physical examination
Sacroiliac joint and paravertebral muscle pressure pain is a positive sign in the early stage of the disease. The following methods can be used to check the progress of sacroiliac joint pain or spinal lesions.
① Occipital wall test: In a healthy person in a standing position with both heels pressed against the root of the wall, the posterior occiput should be close to the wall without gaps. While the gap increases to more than a few centimeters in those with cervical stiffness and/or thoracic segmental deformity of the posterior convexity, resulting in the occiput not being able to fit against the wall.
(ii) Thoracic expansion: the normal value of the difference between the range of thoracic expansion during deep inspiration and deep expiration is not less than 2.5 cm when measured at the level of the 4th rib space, while the thoracic expansion is reduced in those with extensive rib and vertebral involvement.
③Schober test: mark the vertical distance of 10cm above the midpoint of the posterior superior iliac spine line, then ask the patient to bend over (keep both knees in upright position) to measure the maximum forward flexion of the spine, the normal movement increases the distance above 5cm, and the spinal involvement increases the distance <4cm.
④Pelvic compression: the patient lies on his side and compression of the pelvis from the other side can cause pain in the sacroiliac joint.
⑤Patrick’s test (lower extremity “4” test): the patient lies supine with one knee flexed and the heel placed on the contralateral straight knee. The examiner presses the flexed knee with one hand (when the hip is in flexion, abduction and external rotation) and presses the contralateral pelvis with the other hand, and the pain of the contralateral sacroiliac joint can be induced.
4.Imaging examination
The earliest change of AS occurs in the sacroiliac joint. x-ray film shows blurring of the subchondral bone margin of the sacroiliac joint, bone erosion, blurring of the joint space, increase of bone density and joint fusion. The degree of lesions in sacroiliac arthritis is usually classified into 5 grades according to x-ray.
Grade 0: normal.
Grade I: suspicious.
grade II: with mild sacroiliac arthritis.
Grade llI: with moderate sacroiliac arthritis.
Grade IV: joint fusion ankylosis. Radiographs of the spine show vertebral osteoporosis and square changes, small joint obscuration, calcification of the paravertebral ligaments, and bone bridge formation.
Extensive and severe ossifying bridges in the late stage are called “bamboo-like spine”. Bone erosion at the pubic symphysis, sciatic tuberosity and tendon attachment points (e.g. heel bone), with reactive sclerosis and villous changes in adjacent bone, and new bone formation may occur.
5.Laboratory examination
Patients with active disease may have increased erythrocyte sedimentation rate (ESR), elevated C-reactive protein (CRP), mild anemia and mildly elevated immunoglobulins. Although the HLA-B27 positivity rate in AS patients is about 90%, there is no diagnostic specificity because healthy people are also positive. HLA-B27 negative patients cannot be excluded from AS as long as their clinical manifestations and imaging examinations meet the diagnostic criteria.