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Chapter 100: Ankylosing Spondylitis

Heidi S. Chumley

PATIENT STORY

A 43-year-old man falls and presents with acute back and diffuse abdominal pain. He has had back pain on and off for at over 5 years. Also, his wife notes that he has become "stooped" forward in the last few years. The radiographs show flowing ligamentous ossification and syndesmophyte formation about the cervical, thoracic, and lumbar spine consistent with ankylosing spondylitis (bamboo spine) (Figure 100-1). The KUB (kidneys, ureters, bladder) view film also shows fusion of the sacroiliac joints consistent with ankylosing spondylitis (Figure 100-2). No fracture, dislocation, or abdominal pathology is identified. The patient's symptoms are treated and nonsteroidal anti-inflammatory drugs (NSAIDs) are started. On follow-up a blood test reveals that he is human leukocyte antigen (HLA)-B27–positive.

FIGURE 100-1

A. Fusion of the vertebral bodies and posterior elements gives the spine the classic "bamboo" appearance seen in ankylosing spondylitis. B. Note the marked kyphosis and the syndesmophytes that are the thin vertical connections between the anterior aspects of the vertebral bodies. They are located in the outer layers of the annulus fibrosis. (Reproduced with permission from Richard P. Usatine, MD.)

Two x-ray images of the spine: one shows fused vertebrae with no joint spaces; other shows excessively bent spine.
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FIGURE 100-2

Kidney, ureter, bladder (KUB) view showing bamboo spine and fusion of both sacroiliac joints. (Reproduced with permission from Richard P. Usatine, MD.)

An x-ray image of KUB view shows bamboo spine with fused vertebrae, and fusion in both sacroiliac joints.
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TERMINOLOGY

Axial spondyloarthritis is an umbrella term, which includes ankylosing spondylitis (AS) with radiographic findings suggestive of structural damage and patients with axial spine inflammation who do not have radiographic findings (non-radiographic axial spondyloarthritis).

INTRODUCTION

Ankylosing spondylitis is an inflammatory disease of the axial spine associated with the HLA-B27 genotype and radiographic findings. Symptoms of low back and/or hip pain begin in late adolescence or early adulthood. Diagnosis is based on clinical features and radiographic findings.

EPIDEMIOLOGY

  • Prevalence varies by geographic region and is highest in North America and Europe (31.9 and 23.8 per 10,000) and lowest in Latin America and Africa (10.2 and 7.4 per 10,000).1

  • 16% of primary care patients ages 18–45 with chronic low back pain for more than 3 months have ankylosing spondylitis (AS).2

  • AS is more common in males than in females (approximate ratio: 2:1).3

  • Ninety percent of patients are HLA-B27–positive.4 However, many people with HLA-B27 do not develop the disease.

ETIOLOGY AND PATHOPHYSIOLOGY

  • Inflammatory arthritis with a poorly understood pathology.

  • Environment triggers and genetic factors result in inflammation.

  • Chronic inflammation causes extensive new bone formation.

RISK FACTORS

  • Male gender.

  • HLA-B27–positive genotype.

DIAGNOSIS

  • Mean delay of 8 years until diagnosis.5

  • Consider referring/testing patients ...

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