What are the diagnostic criteria for ankylosing spondylitis?

Generally, the diagnosis of ankylosing spondylitis should be made by integrating clinical symptoms, imaging examinations, HLA-B27 genetic testing, inflammatory marker tests, and differential diagnostic results to avoid misdiagnosis or missed diagnosis caused by relying on a single criterion. Detailed analysis is as follows:

1. Clinical symptoms: Inflammatory back pain is the core diagnostic criterion. If a patient experiences lower back or sacroiliac joint pain that does not improve with rest but eases after activity, accompanied by morning stiffness lasting more than 30 minutes and symptoms persisting for at least three months, this condition should be highly suspected.

2. Imaging examinations: Sacroiliac joint lesions are a key characteristic, with different imaging modalities suitable for various clinical scenarios. X-rays can provide an initial assessment of bone sclerosis and joint space abnormalities but have low sensitivity in early stages. CT scans clearly reveal subtle bone erosion and blurred joint surfaces, making them suitable for suspected early-stage cases.

3. HLA-B27 genetic testing: This gene is strongly associated with the disease, with approximately 90% of patients testing positive, compared to only 5%-10% positivity in the general population. It is important to note that a positive result alone does not confirm diagnosis, and a negative result cannot completely rule it out. This test primarily serves as an auxiliary tool; a positive result increases diagnostic likelihood when symptoms or imaging findings are atypical.

4. Inflammatory marker testing: Inflammation activity can be assessed via erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels. Patients during active disease phases often show elevated markers, which supports diagnosis and guides treatment adjustments. However, some patients in stable or early stages may have normal levels, so normal values alone cannot exclude the condition; diagnosis must be made in combination with other criteria.

5. Differential diagnosis: Conditions such as rheumatoid arthritis, psoriatic arthritis, reactive arthritis, and tuberculosis of the sacroiliac joint must be excluded. By comparing symptoms, imaging findings, and specific indicators, these diseases can be accurately differentiated to ensure diagnostic accuracy.

In clinical practice, physicians apply the above criteria flexibly. For example, a young patient presenting with typical inflammatory back pain, a positive HLA-B27 test, and MRI evidence of sacroiliac joint inflammation may receive a diagnosis even if inflammatory markers are normal. Once diagnosed, timely and standardized treatment is necessary. Regular follow-up testing allows for effective disease monitoring and treatment adjustments.