Diagnosis of Ankylosing Spondylitis

Introduction

Ankylosing Spondylitis (AS) is a chronic inflammatory condition primarily affecting the spine and sacroiliac joints. It causes pain, stiffness, and in advanced cases, can lead to fusion of the vertebrae.
Diagnosing Ankylosing Spondylitis can be challenging, especially in the early stages, because its symptoms often overlap with other types of back pain or arthritis. Therefore, a combination of medical history, physical examination, blood tests, imaging studies, and specific diagnostic criteria is used for an accurate diagnosis.

1. Medical History

The first and most important step in diagnosing Ankylosing Spondylitis is a detailed medical history.

Key Points Taken in Medical History:

a. Nature of Pain :- The doctor will ask about the type of back pain whether it improves with rest or movement. In AS, the pain usually improves with physical activity and worsens with rest.

b. Duration of Pain :- Chronic back pain lasting for more than three months is a significant red flag for AS.

c. Age of Onset :- Symptoms typically start between ages 17 to 45.

d. Family History :- A history of AS or related autoimmune diseases in close relatives increases suspicion.

e. Morning Stiffness :- Stiffness lasting more than 30 minutes after waking is common in AS patients.

f. Other Symptoms :- Eye inflammation (uveitis), heel pain, or chest pain may also be reported.

Why Medical History Matters:

• It helps differentiate Ankylosing Spondylitis from mechanical back pain caused by injuries or disc problems.

• Early identification through history can fast-track further diagnostic testing.

2. Physical Examination

After history-taking, a physical examination is crucial to identify the physical signs of inflammation and reduced spinal mobility.

Key Components of Physical Examination:

1. Spinal Flexibility Tests :- The doctor may ask the patient to bend forward, sideways, and backward to assess the range of motion.

2. Schober Test :- A specific test where the doctor measures how much the lower back can bend.

3. Chest Expansion Test :- Restricted chest expansion due to fusion of the rib joints is a classic feature.

4. Sacroiliac Joint Tenderness :- Pressing on the pelvis to check for tenderness at the base of the spine.

5. Posture Assessment :- In advanced cases, a stooped posture (kyphosis) may be seen.

6. Peripheral Joints Check :- Swelling or tenderness in knees, hips, shoulders, or ankles may also occur.

Why Physical Exam Is Important:

• It detects early physical signs that imaging tests may not yet show.

• It helps rule out other causes of back pain or joint disease.

3. Blood Tests

Although no blood test alone can definitively diagnose Ankylosing Spondylitis, certain tests provide supporting evidence.

Important Blood Tests:

a. HLA-B27 Testing :- About 90% of people with AS test positive for the HLA-B27 gene. However, some people without AS may also carry this gene.

b. Inflammatory Markers :- C-Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR) are usually elevated, indicating inflammation.

c. Complete Blood Count (CBC) :- It may show anemia of chronic disease.

d. Other Autoimmune Tests :- Tests like rheumatoid factor (RF) and antinuclear antibody (ANA) are negative in AS, helping to rule out other autoimmune diseases like rheumatoid arthritis.

Why Blood Tests Are Used :- They support the diagnosis when combined with clinical features and imaging findings. They can also help monitor disease activity over time.

4. Imaging Studies

Imaging is a crucial part of confirming the diagnosis and assessing the extent of Ankylosing Spondylitis.

Types of Imaging Used:

a. X-rays :- X-rays of the sacroiliac joints and spine can show characteristic changes. Early signs include erosion and widening of the sacroiliac joints. Later stages show fusion (ankylosis) and “bamboo spine” appearance.

b. MRI (Magnetic Resonance Imaging) :- MRI can detect early inflammatory changes before they are visible on X-rays. Useful in young patients with back pain but normal X-rays.

c. CT Scan (less common) :- Sometimes used to get detailed images of the sacroiliac joints.

Why Imaging Is Crucial :- X-rays and MRI help detect sacroiliitis, a hallmark of AS. MRI helps in early diagnosis when X-rays are still normal. Imaging helps monitor disease progression over time.

5. Use of Diagnostic Criteria

Doctors often use standardized diagnostic criteria to confirm Ankylosing Spondylitis. The most commonly used ones are:

Modified New York Criteria:

• Low back pain and stiffness for more than 3 months that improves with exercise but not rest.

• Limitation of lumbar spine motion in both the sagittal (forward-backward) and frontal (side-to-side) planes.

• Reduced chest expansion compared to normal values for age and sex.

• Radiographic evidence of sacroiliitis.

Diagnosis is confirmed if radiographic sacroiliitis is present along with at least one clinical criterion.

6. Differential Diagnosis

Since back pain is extremely common, doctors must rule out other conditions before confirming AS.

Conditions to Rule Out:

• Mechanical lower back pain (e.g., disc herniation)

• Rheumatoid arthritis

• Psoriatic arthritis

• Reactive arthritis

• Fibromyalgia

• Infectious sacroiliitis

• Degenerative spine diseases

This process is called differential diagnosis and prevents misdiagnosis and wrong treatments.

Conclusion

Because early diagnosis can slow disease progression, preserve spinal flexibility, and improve quality of life, it’s important to seek medical advice as soon as symptoms appear.

If you experience chronic back pain, morning stiffness, or have a family history of AS, do not ignore the symptoms. Early detection and treatment can make a major difference in your journey with Ankylosing Spondylitis.