Ankylosing Spondylitis

Ankylosing Spondylitis

Ankylosing spondylitis is an inflammatory disease of the spine, sacroiliac joints, and occasionally extra-articular structures, including the eye.

It also is known as Marie Strumpell disease. The cause of ankylosing spondylitis is unknown, but autoimmune-mediated mechanisms and environmental factors such as alterations in gut microbiota have been implicated. Approximately 90% of patients with ankylosing spondylitis have the histocompatibility antigen human leukocyte antigen (HLA) B-27 in contrast to 7% of the general population. The significance of this fact is unknown, but this antigen provides the basis for a test to aid in diagnosing the disease. Ankylosing spondylitis is a seronegative arthritis in that no rheumatoid factor antibodies are identifiable in serological testing. Ankylosing spondylitis occurs three times more frequently in men, and symptoms usually appear by the third decade of life. Onset of the disease after age 40 is rare.

Sacroiliitis is often one of the earliest manifestations of ankylosing spondylitis. This finding usually manifests as morning stiffness and a deep aching pain of insidious onset in the low back and over the sacroiliac joints. This stiffness improves with activity and reappears with periods of inactivity. The pain worsens as the disease progresses, and nocturnal exacerbations with significant sleep disturbance are common. Tenderness over the spine, sacroiliac joints, costosternal junction, and greater trochanters is common. Pain and stiffness of the peripheral joints, including the hips and shoulders, are present in 30% to 40% of patients with ankylosing spondylitis. The character of the pain of ankylosing spondylitis is dull and aching, and its intensity is mild to moderate. Occasionally, acute uveitis can occur, as can aortic valvular disease.

What are the Symptoms of Ankylosing Spondylitis

Clinically, a patient with ankylosing spondylitis reports back and sacroiliac pain and stiffness that are worse in the morning and after periods of prolonged activity. The patient may report a limitation of range of motion of the lateral spine and occasionally chest expansion. This limitation of range of motion is due to a combination of bony ankylosis and muscle spasm that the clinician may be able to identify on physical examination. Tenderness to palpation of the iliac crests, greater trochanter, and axial skeleton is a common finding in ankylosing spondylitis. As the disease progresses, the lumbar lordosis disappears, and atrophy of the gluteal muscles may occur. A thoracic kyphosis develops, and the neck is forward flexed. Hip ankylosis may occur with hip involvement, and the patient often compensates with flexion at the knee. Spinal fracture with resultant spinal cord injury may occur as a result of the rigid and inflexible nature of the spine. An abnormal chest expansion test may be present. Anterior uveitis manifests with photophobia, decreased visual acuity, and excessive lacrimation and represents an ophthalmological emergency.

How is Ankylosing Spondylitis diagnosed?

Plain radiographs of the sacroiliac joints usually allow the clinician to diagnose ankylosing spondylitis. Erosion of the sacroiliac joints produces a characteristic symmetrical “pseudowidening” that is diagnostic of the disease, as is squaring of the vertebral bodies, sclerosis of the anterior margins of the vertebral bodies (so-called shiny corners ), and the classic trolley track sign resulting from ankylosis of the facet joints. Magnetic resonance imaging (MRI) of the spine provides the best information regarding the contents of the lumbar spine and sacroiliac joints. MRI is highly accurate and helps identify abnormalities that may put the patient at risk for developing myelopathy. In patients who cannot undergo MRI, such as patients with pacemakers, computed tomography (CT) or myelography is a reasonable second choice. Radionucleotide bone scanning and plain radiography are indicated if fracture or bony abnormality, such as metastatic disease, is being considered in the differential diagnosis.

Although no test is diagnostic for ankylosing spondylitis, finding of the HLA B-27 antigen is highly suggestive of the disease in patients with the previously mentioned clinical findings. This antigen is present in 90% of patients with ankylosing spondylitis. Complete blood cell count may reveal normocytic normochromic anemia. The erythrocyte sedimentation rate is usually elevated, as is the serum immunoglobulin A level.

Differential Diagnosis

Ankylosing spondylitis is a radiographic diagnosis that is supported by a combination of clinical history, physical examination, and laboratory testing. Pain syndromes that may mimic ankylosing spondylitis include low back strain; lumbar bursitis; lumbar fibromyositis; inflammatory arthritis; Reiter syndrome; collagen-vascular diseases; and disorders of the lumbar spinal cord, roots, plexus, and nerves as well as the sacroiliac joints. The clinician should be aware that many other causes of sacroiliitis-related pain exist. Screening laboratory tests, consisting of complete blood cell count, erythrocyte sedimentation rate, antinuclear antibody testing, HLA B-27 antigen screening, and automated blood chemistry testing should be performed if the diagnosis of ankylosing spondylitis is in question to help rule out other causes of the patient’s pain.

Common Causes of Sacroiliitis Related Pain

Psoriatic arthritis
Reiter syndrome
Septic arthritis
Ulcerative colitis
Crohn disease
Synovitis-acne-pustulosis hyperostosis-osteomyelitis (SAPHO) syndrome
Seronegative arthropathies, including ankylosing spondylitis
Intestinal bypass–induced arthritis
Whipple disease


Ankylosing spondylitis is best treated with a multimodality approach. Physical therapy, including exercises to maintain function, heat modalities, and deep sedative massage, combined with nonsteroidal antiinflammatory drugs (NSAIDs) and skeletal muscle relaxants, represents a reasonable starting point. Sulfasalazine may be useful in managing the arthritis associated with the disease. Disease-modifying drugs including methotrexate and biologics including the tumor necrosis factor-α blockers etanercept, infliximab, golimumab, and adalimumab, the interleukin-17A inhibitor secukinumab, and the interleukin-6 inhibitor tocilizumab should be considered in patients who do not respond to NSAIDs. The addition of steroid epidural nerve blocks is a reasonable next step. Caudal or lumbar epidural blocks with a local anesthetic and steroid have been shown to be extremely effective in the treatment of pain secondary to ankylosing spondylitis. Underlying sleep disturbance and depression are best treated with a tricyclic antidepressant compound, such as nortriptyline, which can be started at a single bedtime dose of 25 mg. Acute uveitis should be managed with corticosteroids and mydriatic agents.


Failure to diagnose ankylosing spondylitis accurately may put the patient at risk for developing significant functional disability. Myelopathy, which may progress to paraplegia or quadriplegia, is a serious problem if diagnosis is delayed. Electromyography helps distinguish plexopathy from radiculopathy and helps identify coexistent entrapment neuropathy, such as tarsal tunnel syndrome, which confuse the diagnosis.

Clinical Pearls

The diagnosis of ankylosing spondylitis should be considered in any patient reporting back or sacroiliac pain and stiffness that are worse in the morning or after prolonged periods of inactivity.

Patients with symptoms of myelopathy should undergo MRI on an urgent basis.

Physical therapy combined with NSAIDs may help prevent recurrent episodes of pain and help preserve function.


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