Ankylosing Spondylitis Differential Diagnosis

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Ankylosing spondylitis primarily causes inflammation and pain and affects the joints located between the spinal vertebrae as well as the sacroiliac joints. It is classified as a chronic inflammatory disease. Making an ankylosing spondylitis differential diagnosis involves determining which different diseases and conditions could possibly be causing the patient’s symptoms and is often done through the process of elimination. The signs and symptoms of this condition are not exclusive, therefore, coming to a definitive diagnosis often involves performing a differential diagnosis. It is estimated that one to two percent of the population is affected by this form of arthritis.


Osteoarthritis occurs when the cartilage that is located between bones deteriorates in the joints, and is considered the most common joint disorder, according to MedlinePlus. Ankylosing spondylitis is also a form of arthritis, but is more accurately referred to as a spondyloarthritis. Many of the symptoms are the same, but osteoarthritis tends to affects limb joints, such as the knees, wrists, ankles, elbows, and the joints in the hands. Osteoarthritis also tends to have a later onset. Ankylosing spondylitis’ average onset is in the young adult years, whereas osteoarthritis typically sets in the later adult years. An HLA-B27 antigen test can usually help the doctor eliminate osteoarthritis from his differential diagnosis. Eliminating this will help the doctor eliminate a degenerative cause of the patient’s symptoms.

Inflammatory Conditions

This condition is characterized by inflammation so when making an ankylosing spondylitis differential diagnosis, it is important to rule out other inflammatory conditions. Common inflammatory conditions that doctors may consider include rheumatoid arthritis, psoriatic arthritis, and Reiter’s syndrome (also referred to as reactive arthritis). A rheumatoid factor test can be helpful in ruling out rheumatoid arthritis since about 75 percent of patients with this condition will test positive.

Psoriatic arthritis may also involve the spine making a differential diagnosis a little more difficult. However, if the characteristic psoriasis plaques are present, the doctor can normally rule out this condition.

Reiter’s syndrome, or reactive arthritis, is actually a group of inflammatory conditions involving the eyes, urethra, and joints. Patients may also have lesions on their mucus membranes and skin. Urinalysis and an HLA-B27 antigen test can be done to help rule out this condition along with a genital and urinary tract examination and symptom analysis. Skin and eye symptoms, when present, can also help to rule this condition out.


Ankylosing spondylitis may present with a fever, loss of appetite and weight loss, and other symptoms that could also indicate an infection, such as tuberculosis. Pulmonary tuberculosis is a bacterial infection that primarily affects the lungs. It shares similar symptoms such as fatigue, unintentional weight loss, and fever. Breathing symptoms may help to rule this condition out if they are present. Testing will most likely be done, however, to completely rule out this condition. Such testing may include a chest x-ray, tuberculin skin test, and bronchoscopy.


MDGuidelines. (2010). Ankylosing Spondylitis. Retrieved on October 14, 2010 from MDGuidelines: (2009). Ankylosing Spondylitis. Retrieved on October 14, 2010 from