120: Ankylosing Spondylitis

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CHAPTER 120

Ankylosing Spondylitis

George W. Deimel, IV, MD; Steven E. Braverman, MD

Synonyms

Seronegative spondyloarthropathy

Seronegative arthritis

Seronegative spondylarthritides

ICD-9 Code

720.0  Ankylosing spondylitis

ICD-10 Codes

M45.0  Ankylosing spondylitis of multiple sites in spine

M45.1  Ankylosing spondylitis of occipito-atlanto-axial region

M45.2  Ankylosing spondylitis of cervical region

M45.3  Ankylosing spondylitis of cervicothoracic region

M45.4  Ankylosing spondylitis of thoracic region

M45.5  Ankylosing spondylitis of thoracolumbar region

M45.6  Ankylosing spondylitis of lumbar region

M45.7  Ankylosing spondylitis of lumbosacral region

M45.8  Ankylosing spondylitis of sacral and sacrococcygeal region

M45.9  Ankylosing spondylitis of unspecified sites in spine

Definition

Ankylosing spondylitis is a chronic, inflammatory, rheumatologic disorder that primarily affects the spinal column and sacroiliac joints. It is classified as a seronegative spondyloarthropathy. Enthesitis (inflammation of the soft tissues attaching tendons, ligaments, and joint capsules to bone), synovitis, and inflammation of the synovial capsule are characteristic of its involvement. The most common sites include sacroiliac, apophyseal, and discovertebral joints of the spine; costochondral and manubriosternal joints; paravertebral ligaments; and attachments of the Achilles tendon and plantar fascia. Peripheral joint involvement is less common but occurs in the more severe forms of the disease or with younger age at onset [1].

The onset of symptoms is usually in late adolescence or early adulthood, and there is a 3:1 male predilection. It is not associated with the presence of rheumatoid factor or antinuclear antibodies. Although there is a genetic association with the HLA-B27 histocompatibility antigen (approximately 90% of ankylosing spondylitis patients express the HLA-B27 genotype), this antigen has not proved to be an adequate screening marker as only 5% of individuals with the HLA-B27 genotype contract the disease. Thus, HLA-B27 is not necessary to confirm the diagnosis [2].

Symptoms

Inflammatory spondyloarthropathies should be considered in any young adult patient who complains of insidious onset, progressively worsening, dull, thoracolumbar or lumbosacral back pain. Other characteristics that should raise suspicion for inflammatory-mediated axial disease include back pain that improves with exercise, shows no improvement with rest, and is responsive to nonsteroidal anti-inflammatory medications and pain at night [3].

Ankylosing spondylitis can have a variable presentation, but sacroiliac pain is a common complaint along with progressive morning stiffness and prolonged stiffness after inactivity. Tendon and ligament attachment sites may become painful and swollen, and one third of patients may have hip or shoulder pain. Chest pain with deep breathing and eye pain with blurred vision, floaters, and photophobia are late symptoms of more severe disease [4]. Neurologic symptoms, such as paresthesias and motor weakness, are usually absent.

Physical Examination

The most typical findings on physical examination are signs of decreased spine mobility and pain at sites of ligament and tendon attachments. Tests of spinal mobility include the modified Schober test, finger to floor distance, cervical rotation, occiput to wall distance, and chest expansion. The modified Schober test is performed with the patient initially standing in erect position. The examiner identifies the posterosuperior iliac crest line (i.e., lumbosacral junction) and makes two midline marks, one 10 cm above the iliac crest line and one 5 cm below the iliac crest line. The patient is then instructed to perform forward trunk flexion while the examiner measures the distance between the two marks. Normal spinal mobility is indicated by an increase of more than 5 cm or a total distance of more than 20 cm; an increase of less than this would suggest limited lumbar spine mobility. The inability to touch the occiput to the wall while standing against it and the inability to expand the chest by more than 3 cm in full inhalation are late findings in the disease [5].

On palpation of the spine, the lower paraspinal muscles and sacroiliac joints may be tender. A Gaenslen test result may also be positive (Fig. 120.1). Palpation of extremities demonstrates pain at attachment sites of ligaments and tendon (enthesitis), particularly around the heel (e.g., calcaneal enthesitis) and knee (i.e., tibial tuberosity). Peripheral joint swelling and pain with decreased range of motion can be seen in 25% to 30% of patients. A discolored and edematous iris with circumferential corneal congestion occurs in iritis and anterior uveitis. The neurologic evaluation is typically normal with regard to motor, sensory, and reflex examination findings. Weakness may be noted, but it is usually associated with pain, loss of mobility, or disuse.

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FIGURE 120.1 Gaenslen test. A, With the patient in side-lying position, the clinician extends the test leg. B, With the patient supine, the test leg is extended over the edge of the table. Pain in the sacroiliac joints indicates a positive test result.

Functional Limitations

The functional limitations of the patient with ankylosing spondylitis are typically related to spine pain and immobility. The three best predictors of decreased spinal mobility are cervical rotation, modified Schober test, and finger to floor distance, although these measurements have not correlated with the patient’s assessment of disease activity [5,6]. Early in the disease process, decreased spine range of motion is secondary to back pain and muscle spasms. Most dysfunction is mild and self-limited, typically improving with treatment. In severe disease, positioning from hip flexion contractures, thoracic kyphosis, and loss of cervical rotation decrease patients’ ability to view activities in front of them and side to side. The most commonly reported activity limitations are interrupted sleeping, turning the head while driving, carrying groceries, and having energy for social activities [7]. Limitations in chest wall motion lead to a reliance on diaphragmatic breathing and a secondary drop in aerobic capacity. Pain, posture, and functional impairments can also significantly affect sexual relationships [8].

The Bath Ankylosing Spondylitis Functional Index and the Dougados Functional Index are functional assessment tools used by clinicians specializing in the care of patients with ankylosing spondylitis that provide a measure of daily function [911]. Past studies have shown that approximately 90% of patients with ankylosing spondylitis remain employed, although recent evidence suggests that up to one third of patients experience some form of employment disruption because of pain and physical limitations [4,6,12].

Diagnostic Studies

There is a well-documented lag time between initial onset of symptoms and diagnosis that ranges from 7 to 11 years [13]. Given the lack of specific signs and symptoms for early ankylosing spondylitis, a high level of suspicion is required in young patients presenting with back pain. Laboratory investigation should include inflammatory markers: erythrocyte sedimentation rate and C-reactive protein [11]. Although neither is required for diagnosis and approximately 40% of patients will have normal values, the elevation of acute phase reactants can indicate severity, responsiveness to treatment, peripheral joint involvement, or extra-articular disease. HLA-B27 is present in 90% of patients with ankylosing spondylitis. A negative test result suggests milder disease with a better prognosis. Rheumatoid factor and antinuclear antibodies are absent.

Radiography of the spine and pelvis is the standard imaging modality in diagnosis and assessment of disease, although computed tomography and magnetic resonance imaging are more sensitive for detection of bone changes, especially early in the disease course and particularly in the assessment of the sacroiliac joints [14

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