Overview
Ankylosing spondylitis (AS) is a chronic progressive disease that mainly affects the sacroiliac joints, spinal prominences, paraspinal soft tissues and peripheral joints, and may be accompanied by extra-articular manifestations. In severe cases, spinal deformity and joint ankylosis may occur. The prevalence rate in China is 0.26%, and the ratio of men to women is 5:1, except that the onset of disease is slower and less severe in women. The age of onset is usually from 13 to 31 years old, and it is rare after 30 years old and before 8 years old.
Clinical manifestations
The onset of the disease is insidious. Patients gradually develop pain and/or stiffness in the low back or sacroiliac region, waking up in the middle of the night with pain, difficulty turning over, and stiffness in the low back is obvious when rising in the morning or after sitting for a long time, but relieved after activity. Some patients feel dull pain in the buttocks or severe pain in the sacroiliac region, which occasionally radiates to the periphery. The pain can be aggravated by coughing, sneezing, or sudden twisting of the back. In the early stage of the disease, the pain is mostly intermittent on one side, and after a few months, the pain is mostly persistent bilaterally. As the disease progresses from the lumbar spine to the thoracic and cervical spine, pain, restricted movement or spinal deformity occurs in the corresponding area. The systemic manifestations of the disease are mild, with a few severe cases having fever, fatigue, emaciation, anemia, or other organ involvement. Plantar fasciitis, Achilles tendinitis, and other areas of tendon terminal disease are common in this disease. 1/4 of patients develop uveitis during the course of the disease, alternating unilaterally or bilaterally, which usually resolves spontaneously and can cause visual impairment with repeated attacks. Neurological symptoms arise from compressive spinal neuritis or sciatica, vertebral fractures or incomplete dislocations, and cauda equina syndrome, the latter of which can cause impotence, nocturnal urinary incontinence, bladder and rectal dullness, and loss of ankle reflexes. Very few patients develop fibrosis of the upper lobe of the lung. It is sometimes accompanied by cavity formation and is considered tuberculosis, and may be exacerbated by concurrent mycobacterial infections. Aortic atresia and conduction disorders are seen in 3.5-10% of patients. AS can be complicated by IgA nephropathy and amyloidosis.
Physical examination
Sacroiliac joint and paravertebral muscle pain is a positive sign in the early stage of the disease. As the disease progresses, the anterior lumbar convexity flattens, the movement of the spine is limited in all directions, the extension of the thorax is reduced, and the cervical vertebrae protrude posteriorly. The following methods can be used to examine the progression of sacroiliac joint compression pain or spinal lesions.
(1) Occipital wall test: In a normal 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 a gap. In the case of cervical stiffness and/or posterior convexity of the thoracic vertebral segment, the gap increases to more than a few centimeters, resulting in the occipital area not being able to fit the wall.
(2) 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 those with extensive rib and vertebral involvement have reduced thoracic expansion.
(3) Schober test: mark the midpoint of the posterior superior iliac spine at a vertical distance of 10 cm above and 5 cm below, and then ask the patient to bend over (keeping both knees in an upright position) to measure the maximum forward flexion of the spine.
(4) Pelvic compression: the patient lies on his side and pressing the pelvis from the other side can cause sacroiliac joint pain.
(5) Patrick’s test (lower extremity 4-way test): The patient lies supine with one knee flexed and the heel placed on the opposite knee that is straight. The examiner presses the flexed knee with one hand (the hip is in flexion, abduction and external rotation) and presses the contralateral pelvis with the other hand, and the pain in the contralateral sacroiliac joint can be elicited. Those with knee or hip lesions cannot complete the 4-character test either.
Imaging]
The earliest changes in AS occur in the sacroiliac joint. X-rays of this area show blurring of the subchondral bone margin, bone erosion, blurring of the joint space, increased bone density and joint fusion. The degree of lesion of sacroiliac arthritis on X-ray is usually classified into 5 grades: grade 0 is normal, grade I is suspicious, grade II has mild sacroiliac arthritis, grade III has moderate sacroiliac arthritis, and grade IV has joint fusion ankylosis. Computed tomography (CT) should be used in clinically suspicious cases where the X-ray has not yet shown clear or grade II or higher bilateral sacroiliac arthritic changes. This technique also has the advantage of having fewer false positives. However, because the upper part of the sacroiliac joint anatomy is ligamentous, the irregularity and widening of the joint space on imaging caused by its attachment makes the judgment difficult. In addition, subchondral aging of the iliac portion of the sacroiliac joint similar to joint space narrowing and erosion is a natural phenomenon and should not be considered abnormal. Magnetic resonance imaging (MRI) is better than CT for understanding cartilage lesions, but it is prone to false positive results in determining sacroiliac arthritis, and because it is expensive, it should not be done as a routine test at present.
Radiographs of the spine show vertebral osteoporosis and square changes, blurring of the vertebral tuberosities, calcification of the paravertebral ligaments, and bone bridge formation. Extensive and severe ossifying bridges in advanced stages 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 bones, and new bone formation may occur.
Laboratory tests
In active patients, increased blood sedimentation, increased C~reactive protein and mild anemia are seen. Rheumatoid factor is negative and immunoglobulins are mildly elevated. Although the HLA-B27 positivity rate in AS patients is about 90%, it is not diagnostic specific because normal people also have HLA-B27 positivity. HLA-B27 negative patients cannot be excluded from AS as long as their clinical manifestations and imaging examinations meet the diagnostic criteria.
[Diagnostic criteria].
①The duration of lower back pain lasts for at least 3 months, and the pain improves with activity but is not relieved by rest;
②Lumbar spine movement is limited in anterior-posterior and lateral flexion direction;
③Thoracic extension range is less than the normal value for the same age and sex;
④Bilateral sacroiliac arthritis grade II~IV, or unilateral sacroiliac arthritis grade III~IV. The diagnosis of AS can be confirmed if the patient has ④ and any one of ①~③ respectively.
Treatment options]
There is no cure for AS. However, if patients are diagnosed and treated in a timely manner, they can achieve symptom control and improve their prognosis. A combination of non-pharmacological, pharmacological and surgical treatment should be used to relieve pain and stiffness, control or reduce inflammation, maintain good posture, prevent deformation of the spine or joints, and correct deformed joints if necessary, in order to improve and enhance the patient’s quality of life.
Prognosis]
It should be emphasized that the severity of the disease varies greatly in clinical manifestations, with some patients experiencing repeated and continuous progression of the disease, while others remain relatively quiescent for a long time and can work and live normally. However, the prognosis is poor in patients with younger age of onset, earlier involvement of the hip joint, recurrent episodes of iridocyclitis and secondary amyloidosis, delayed diagnosis, untimely and unreasonable treatment, and non-adherence to long-term functional exercise. In conclusion, this is a chronic progressive disease and should be followed up for a long time under the guidance of a specialist.