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
General Symptoms of AS
- 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.
Ankylosing spondylitis 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.