The term “spondyloarthritis” is used to describe an overlapping group of diseases that are characterized by inflammation of the sacroiliac joints (sacroiliitis); axial spine (spondylitis); tendon, fascia, and ligament insertion sites (enthesitis); and, in some patients, an oligoarthritis, rash, or inflammatory eye disease (uveitis). This group of diseases has also been referred to as seronegative spondyloarthritis based on the absence of rheumatoid factor. These diseases include ankylosing spondylitis, psoriatic arthritis, the arthritis of inflammatory bowel disease, and reactive arthritis. Although these conditions share common features, each one has distinct clinical and epidemiologic characteristics (Table 17–1). However, in some patients, especially early in the disease presentation, the diagnosis is not clear; these patients are considered to have undifferentiated spondyloarthritis. The overall prevalence of these conditions has been estimated to be between 0.5% and 1.5%.

The entheses are an important site of inflammation and subsequent pathology in spondyloarthritis. These are locations where tendons, fascia, and ligaments insert into bone. Clinical manifestations include heel pain with involvement of the Achilles tendon, foot pain at the site of insertion of the plantar aponeurosis, or swelling of an entire digit (dactylitis or sausage digit) due to inflammation of the flexor and extensor tendons of the fingers or toes.

Histologically, the synovial inflammation in spondyloarthritis is characterized by chronic inflammatory infiltrates that are nonspecific and indistinguishable from that of rheumatoid arthritis. While erosive bone disease does occur, unlike the rheumatoid process, this inflammatory process is also accompanied by new bone formation across previous articulations. This ossification of the articular and ligamentous structures of the spine leads to syndesmophyte formation and may result in eventual fusion and characteristic radiographic findings.

The dominant clinical problems that bring the patient with spondyloarthritis to a clinician and require careful management over many years are axial pain, limitation of motion, and deformity of the spine. In all forms of spondyloarthritis, the same principles of diagnosis and management of the axial problem apply with attention directed to the cutaneous, gastrointestinal, ocular, and peripheral articular manifestations of the primary disorder.

Essentials of Diagnosis

• Inflammatory back pain in young adults.
  
• Radiographic demonstration of sacroiliitis.
  
• Reductions in spinal mobility, particularly lumbar flexion.
  
• Association with anterior uveitis.
  
• Increased relative risk conferred by inheritance of HLA-B27.
  
• Positive family history.

General Considerations

The pathogenesis of spinal inflammation is unknown; however, there is a strong hereditary component marked by the only known susceptibility gene, HLA-B27. This genetic marker is strongly associated with sacroiliitis and spondylitis regardless of clinical setting. More than 85% of patients with ankylosing spondylitis have HLA-B27. The prevalence of ankylosing spondylitis parallels the frequency of HLA-B27 in different populations in the United States and in other regions of the world. This gene occurs in 8–10% of white Americans, and the disease occurs in 0.1–0.2% of that population. Blacks have a much lower frequency of both disease and the HLA-B27 gene. On the other hand, there is a high frequency of spondylitis and of HLA-B27 in certain Native American and Eskimo groups. Ankylosing spondylitis is common in Europeans and most Asian groups but is found rarely in Japanese, again reflecting the relative frequency of the B27 marker. If normal persons with HLA-B27 are carefully assessed, clinical or radiographic evidence of disease can be found in only 2%.

The typical patient with ankylosing spondylitis is a young white man under the age of 40 years (Table 17–2). Occasionally, the diagnosis is made in older patients, but careful questioning often reveals that symptoms began years earlier. The impression that women are affected less often than men (ratio 1:3) may be caused by underrecognition of the disease in women. The initial symptoms of the disorder in women may include more peripheral joint or cervical spine involvement. Therefore, one should be mindful of these differences between men and women and must consider an emerging process in young women in whom arthritis presents.

Clinical Findings

Symptoms and Signs

Axial Spine

The usual presenting symptom of ankylosing spondylitis is inflammatory back pain. The pain and stiffness are in the low back or deep within the buttocks. This discomfort begins insidiously, and the patient would typically have noticed this for several months to several years before seeking medical attention. Unlike mechanical low back syndromes, the pain and stiffness of inflammatory disease are usually worsened by rest and improved by exercise. The patient may be unable to sleep through the night or sit for prolonged periods and must arise and stretch to obtain relief, with morning stiffness lasting greater than 30 minutes. As in discogenic disease, however, symptoms of shooting pains into the buttocks and down the posterior or lateral thighs may occur and mimic sciatica. These pains are usually transient, may alternate to the opposite side and are not associated with any demonstrable neurologic deficits. There are few measurable abnormalities in patients with early disease (Table 17–3). In fact, the patient with sacroiliitis may have an entirely normal physical examination despite significant symptoms of pain and stiffness in the low back region, contributing to delays in diagnosis. At most, there may be tenderness on direct palpation of these joints in the buttocks or on compression of the pelvis.

Abnormalities that eventually appear in the patient with progressive disease relate to loss of range of motion and deformity in mobile structures. The patient with lumbar involvement has often lost the normal lordosis, and there is flattening of that segment of the back. In addition, there is loss in range of motion when the patient attempts to bend forward. It should be recalled that hip motion accounts for 90 degrees of the flexion of the trunk on the lower extremities and that the lumbar spine provides the remaining stretch by reversing its lordosis and becoming kyphotic. An objective measurement of lumbar motion is the Schober test. With the patient standing erect, a horizontal line is drawn at the L5–S1 region at the level of the sacral dimples and another line 10 cm above that in the midline of the back. With forward flexion, the distance between these two ends of the 10-cm line should increase from 10 cm to 15 cm in the normal lumbar spine. A modified Schober test is negative if the distance between the 5 cm mark below the sacral dimples and the 10 cm above it increases to 20 cm on forward flexion. Lateral lumbar flexion is assessed by having the patient bend laterally without flexing forward or bending the knees, with measurements scored between the middle finger and the floor. A difference of >10 cm from start to end positions is normal. These tests are best applied and interpreted in the young patient because lumbar motion normally decreases with age.

Involvement of the thoracic spine is determined subjectively by the patient’s description of pain or stiffness in that region and by demonstrable tenderness along the vertebral column and paravertebral muscles. Compression of the rib cage laterally and over the sternum may also elicit discomfort. Objective determination of fusion of the costovertebral joints is obtained by measuring the chest expansion. A tape measure is placed around the patient’s chest wall at the nipple line or fourth intercostal space, and the change in circumference from full expiration to full inspiration is measured. Less than 2.5 cm is considered abnormal.

The range of motion of the cervical spine should be determined; extension, right and left rotation, lateral flexion, and forward flexion should be measured. Loss of extension is usually the earliest abnormality, and as the disease progresses, fixed deformity in the forward flexed position tends to develop. Developing cervical kyphosis is assessed by the occiput-to-wall measurement. The patient places both heels against the base of the wall and attempts to extend the neck fully to touch the wall with the back of the head. If this is accomplished readily, then extension measurement is normal.

Peripheral Arthritis