Ankylosing Spondylitis (AS)
by Dr. David Borenstein M.D. updated 11.2018
Spondyloarthritis is an immune-mediated chronic inflammation of the structures of the spine. A normal immune system fights off infections and kills abnormal cells that can grow into can grow into cancers. In people with spondyloarthritis, immune cells localized in different areas of the spine become activated and start damaging your own tissues. These inflamed tissues produce chemical signals released into the blood stream that recruit additional immune cells. The end result is chronic inflammation that can destroy tissues. In the setting of spondyloarthritis, the end result of this inflammatory process is the calcification of spinal structures. The spine can become fused.
Most commonly, four illnesses can cause spondyloarthritis. Ankylosing spondylitis, psoriatic spondylitis, reactive arthritis, and arthritis associated with inflammatory bowel disease can cause characteristic changes in the spine. Each illness has its own distinctive characteristics in regard to initiating the illness and it primary manifestations. Therapies for these illnesses are similar but not identical because of the associated underlying illness causing the spinal disease.
What are the Symptoms of Ankylosing Spondylitis?
About 2% of the population of the United States has AS. Similar numbers of individuals are affected in countries around the world. AS tends to run in families. Genetic predisposition is related to the presence of a specific genetic marker, Histocompatibility Leucocyte Antigen (HLA) – B27. Approximately 90% of AS individuals are HLA-B27 positive. This genetic marker is not sufficient to have the disease. Approximately 8% of the population of the USA is B27 positive but do not have disease. Some additional factor is needed to have the illness above and beyond the genetic marker. The frequency of men to women is 3 to 1, but may be an overestimation. AS may be milder in women and is under diagnosed.
Symptoms related to inflammation of the musculoskeletal system include
- Prolonged morning stiffness of the spine lasting hours
- Spine stiffness associated with sitting for variable lengths of time
- Back pain improvement with exercise
- Eye inflammation – iritis
- Radiating leg pain – pseudosciatica
- Disordered sleep
- Mild weight loss
The usual AS patient has moderate degree of intermittent aching pain localized to the low back to start. The muscles on the side of the spine can contribute to pain because of spasms. With progression of AS, the chest and neck develop pain associated with decreasing motion. The low back becomes more difficult to move. Breathing may be affected when moving ribs becomes painful. In a majority of patients, the initial symptoms are low back pain and stiffness. Pain in hips or shoulders is the initial complaint in a minority. Woman may present with neck stiffness prior to low back complaints.
An enthesis is the anatomic structure that attaches tendons and ligaments to bones. Enthesitis is inflammation of this structure and is a characteristic finding in spondyloarthritis. A common location for this inflammation is the Achilles tendon and plantar fascia on the bottom of the foot.
AS is more than a skeletal disease. Current therapy has limited the appearance of these extra-articular manifestations of disease, but is present in individuals who have extensive disease. Iritis is a form of eye inflammation where looking into a light is painful. Iritis occurs in about 25% of AS patients. Individuals with uncontrolled disease for 30 years or longer may have inflammation of the heart particularly involving the aortic valve. Aortic valve disease can cause heart failure and abnormal heart beats. Involvement of the thoracic spine can affect lung function because of decreased movement of the chest wall. Scarring of the upper most portion of the lung occurs.
How is Ankylosing Spondylitis Diagnosed?
The diagnosis of AS is based upon a spectrum of characteristic findings noted in the history physical examination, and radiographic findings. Inflammatory back pain is characterized by the presence of back pain for longer than 3 months in association with an age of onset before 40 years, no improvement with rest, improvement with exercise, insidious onset, and pain increased at night. Plain xray films of the lower spine will show definite signs of arthritis in the sacroiliac joints. Laboratory findings of HLA-B27 positivity, and blood test signs of inflammation (elevated C reactive protein or erythrocyte sedimentation rate) are compatible but not specific for AS.
Inflammation of AS starts before Xray findings is identified. This is thought of as a pre-radiographic form of AS. In these individuals with early AS, MR scan of the spine can identify inflammation in areas of the spine compatible with the diagnosis.