Porth's Essentials of Pathophysiology, 4e

1126

Musculoskeletal Function

U N I T 1 2

Ankylosing Spondylitis Ankylosing spondylitis is a chronic, systemic inflamma- tory disease of the joints of the axial skeleton manifested by pain and progressive stiffening of the spine. 3,4,51 The disease usually begins in late adolescence or early adult- hood. The incidence is greater in men than in women, and symptoms are generally more prominent in men. Pathogenesis. Although the pathogenesis of ankylos- ing spondylitis has not been established, the presence of mononuclear cells in the acutely involved tissue suggests an immune response. Epidemiologic findings indicate that genetic and environmental factors play a role in the pathogenesis of the disease. The HLA-B27 allele remains one of the best-known examples of an association between a disease and a hereditary marker. Approximately 90% of those with ankylosing spondyli- tis possess the HLA-B27 allele, which also is present in approximately 5% to 15% of the normal population. 4 Several theories have been advanced to account for the association between HLA-B27 and ankylosing spondy- litis. One possibility is that it predisposes to ankylosing spondylitis by influencing the body’s endogenous flora. 52 Clinical Manifestations. The typical musculoskeletal lesion associated with ankylosing spondylitis is inflamma- tion, or enthesitis , at sites where tendons and ligaments attach to bones. Typically, the disease process begins with bilateral involvement of the sacroiliac joints and then moves to the smaller joints of the posterior elements of the spine (Fig. 44-8). The result is ultimate destruction of these joints with ankylosis or posterior fusion of the spine. The vertebrae take on a squared appearance and bone bridges fuse one vertebral body to the next across the intervertebral disks. 51 Progressive spinal changes usually begin with the sacroiliac area and then move up the spine to involve the costovertebral joints and cervi- cal spine. Occasionally, large synovial joints (i.e., hips, knees, and shoulders) may be involved. The disease spec- trum ranges from an asymptomatic sacroiliitis to a pro- gressive disease that can affect many body systems. The usual presenting symptom is back pain that may be persistent or intermittent. 3,4,51 The pain, which becomes worse when resting, particularly when lying in bed, may also involve the buttocks and hip areas, and can radiate to the thigh in a manner similar to that of sciatic pain. Mild physical activity or a hot shower helps reduce pain and stiffness. Sleep patterns frequently are interrupted because of thesemanifestations.Walking or exercisemay be needed to provide the comfort needed to return to sleep. The most common extraskeletal involvement is acute anterior uve- itis (iritis), which occurs in approximately 30% of persons sometime in the course of their disease. Systemic features of weight loss, fever, and fatigue may be apparent. Osteoporosis may occur, especially in the spine, which contributes to the risk of spinal fracture. Loss of motion in the spinal column is characteristic of the disease (see Fig. 44-8). Loss of lumbar lordosis occurs as the disease progresses, and this is followed by kyphosis of the­ thoracic spine and extension of the neck. A spine fused

Eyes: Uveitis

Kyphosis and extension of the neck

Enthesitis (inflammation and tendency for fibrosis and calcification at sites of muscle insertion) at shoulders, hips, knees, and heels

Enthesitis of costovertebral and costosternal junctions with flexion contraction of the diaphragm

Spinal column fused by ossification of disks, joints, and ligaments

FIGURE 44-8. Clinical manifestations of ankylosing spondylitis.

in the flexed position is the end result of severe ankylos- ing spondylitis. A kyphotic spine makes it difficult for the patient to look ahead and to maintain balance while walking. The image is one of a person bent over look- ing at the floor and unable to straighten up. X-ray films show a rigid, bamboolike spine. The heart and lungs are constricted in the chest cavity. Abnormal weight bearing can lead to degeneration and destruction of the hip joint, necessitating joint replacement procedures. Peripheral arthritis is more common in the hips and shoulders. Diagnosis andTreatment. The diagnosis of ankylosing spondylitis is based on history, physical examination, and x-ray examination. 51,53 The history and physical examination should include measures of physical func- tion, pain, spinal mobility, duration of morning stiff- ness, involvement of peripheral joints and entheses, and fatigue. Laboratory findings frequently include an