Ankylosing Spondilitis

A 22-year-old man is evaluated in the office for a 12-month history of gradually worsening low back stiffness that is present for 2 hours after awakening in the morning. He has significant fatigue but no fever, chills, night sweats, or weight loss. He does not have pains in the peripheral joints but does have bilateral buttock pains throughout the day on sitting. One year ago, he also had a 2-week episode of uveitis of the right eye, which responded to corticosteroid eye drops.

On physical examination, vital signs are normal. He appears healthy but walks with a mild forward bending of his spine. Deep pressure and palpation of the lumbar spine in the midline and both sacroiliac joints elicits tenderness. Chest expansion in the fourth intercostal space is 2 cm (normal ≥5 cm), and he can only reach the midcalf region when attempting to touch his fingers to the floor.

On laboratory studies, hemoglobin is 12.5 g/dL, erythrocyte sedimentation rate is 85 mm/h, and C-reactive protein is 5 mg/dL. Anteroposterior radiograph of the pelvis and sacroiliac joints is shown




Which of the following is the most likely diagnosis?
A Ankylosing spondylitis
B Metastatic cancer
C Osteoarthritis
D Sacral fracture

ANSWER

This patient most likely has ankylosing spondylitis, a systemic inflammatory disorder that most commonly occurs in men and primarily involves the spine and sacroiliac joints. Ankylosing spondylitis should be considered in the following : patients <40 years of age, patients with insidious onset of chronic low-back pain and stiffness of >3 months' duration; and those with low-back pain and stiffness that worsen at night or after prolonged rest or physical inactivity and are alleviated with physical activity or a hot shower. Within 6 to 12 months after disease onset, sacroiliac joint damage occurs and is manifested by narrowing and erosions, as seen on this patient's radiograph. The earliest finding is fuzziness and irregularity of the sacroiliac articular surface. Ankylosing spondylitis is later associated with subchondral sclerosis. These findings are first detected and are more marked on the iliac side of the joint. The erosion of the joint surface can cause erosions in and irregularity (serration) of the subchondral bone. The concomitant pseudo-widening of the joint space later leads to gradual joint space narrowing. The inflammatory process results in healing and bone formation that ultimately bring about fusion of the sacroiliac joints. Inflammatory changes also begin in the T12–L1 region of the spine and eventually lead to ossification of the outer fibers of the annulus fibrosis and the development of syndesmophytes. In the most severe cases of ankylosing spondylitis, “bamboo spine” develops, which is associated with soft tissue and bony changes that reflect this condition's inflammatory and calcifying nature.

Sacral fracture usually occurs in patients with osteoporosis and is triggered by seemingly minor episodes of trauma. Osteoarthritis of the spine or sacroiliac joints is common in older patients and is manifested by spur formation originating in the corners of the vertebrae and disk-space narrowing. In addition, pain in osteoarthritis, as well as mechanical back pain, is alleviated by a night of rest and worsens as the day progresses; conversely, low back pain in ankylosing spondylitis occurs because of inflammation and is therefore worse in the morning and is alleviated as the day progresses. Cancer of the spine or pelvis most often occurs in older patients because of metastatic disease and would be unusual in an otherwise healthy 22-year-old man. Furthermore, metastatic disease is associated with severe pain during the day and night. Imaging studies in this setting typically reveal lytic or blastic lesions.


Key Point
Consider ankylosing spondylitis in patients <40 years with insidious onset of chronic low-back pain and stiffness of >3 months' duration and low-back pain and stiffness that worsen at night or after prolonged rest or physical inactivity.