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by David Borenstein M.D. updated 2/2021

A normal immune system fights off infections and kills abnormal cells that 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.

Symptoms & Signs of Ankylosing Spondylitis

Approximately 2% of individuals in the United States will have 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

  • Fatigue
  • Disordered sleep
  • Mild weight loss
  • Fever

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.

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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.

Diagnosis of Ankylosing Spondylitis

Clearing the Confusion involving Axial Spondyloarthritis, Ankylosing Spondylitis, and Nonradiographic Spondyloarthritis

Inflammatory spinal disease is a complicated issue for doctors and patients alike. A number of names are associated with a spectrum of clinical complaints including chronic low back, physical limitations including limited spine motion, laboratory findings associated with a genetic predisposition, and radiographic findings affecting some or all of the specific parts of the spine. Some of the names associated with inflammatory spinal disorders include axial spondyloarthritis, ankylosing spondylitis, and nonradiographic spondyloarthritis. Defining these groups can help lift some of the confusion that surrounds these illnesses.

Axial spondyloarthritis (axSpA) is the general designation used for disabling forms of inflammatory arthritis of the spine. axSpA includes disorders associated with chronic low back pain usually found in individuals younger than 45 years in age. Some of these patients in this group may also have articular damage in joints outside of the spine. axSpA may also have non-joint findings including eye inflammation (uveitis), skin rash (psoriasis), reaction to an infection (reactive arthritis) and gastrointestinal disorders (inflammatory bowel disease). Patients with axSpA which affect the spine primarily belong to two subtypes. These two subtypes are ankylosing spondylitis(AS) and nonradiographic spondyloarthritis (nr-axSpA).

Ankylosing spondylitis (AS) is an inflammatory spinal disease which is associated with varying degrees of spinal fusion. The diagnosis of AS is based upon 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 increased pain at night. A finding for classic AS is the finding of specific findings on plain x-rays showing definite signs of sacroiliac joint damage. Laboratory findings of histocompatibility-B27 positivity, and blood test findings for inflammation (elevated C reactive protein or erythrocyte sedimentation rate) are compatible but no specific for a diagnosis of AS.

Nonradiographic spondyloarthritis (nr-axSpA) Not all patients who have axSpA have plain x-ray changes in the sacroiliac joints. These patients have clinical symptoms of inflammatory back pain and are HLA-B27 positive, but do not have definitive plain x-ray alterations in the sacroiliac joints. Magnetic resonance imaging of the sacroiliac joints is needed to identify the presence of inflammation in the form of bone marrow edema. These individuals do not meet criteria for AS but do have an inflammatory arthritis of the spine. These patients have non-radiographic spondyloarthritis. Questions remain regarding whether nr-SpA is AS in its earliest form but is a disease independent of AS. This question will be answered over time since these designations have only been defined since the advent of MRI. Longitudinal studies will need to be completed to know the answer to this question.


  1. Rudwaleit M et al: The challenge of diagnosis and classification in early ankylosing spondylitis: do we need new criteria? Arthritis Rheum. 2005:52(4) 1000 -1008
  2. Wang R et al. Progression of nonradiographic axial spondyloarthritis to ankylosing spondylitis:A population-based cohort study. Arthritis Rheumatol 2016;68:1415-1421