Ankylosing spondylitis: Clinical sciences

Ankylosing spondylitis, or AS for short, is a chronic inflammatory condition characterized by arthritis that primarily affects the spine. This chronic inflammation gradually erodes the lower spine, especially the sacroiliac joints, resulting in ankylosis or joint fusion, stiffness, and back pain. Ankylosing spondylitis is a type of spondyloarthropathy, which is a series of related conditions characterized by inflammation affecting the spine, entheses, and joints.

Now, if your patient presents with a chief concern suggesting ankylosing spondylitis, the first step is to perform a focused history and physical examination.

Your patients will usually be biological males less than 45 years old. They will typically report progressive low back pain and stiffness that has lasted three months or more. The pain and stiffness are worse in the morning and improve with activity, not rest. 

Next, family history might be positive for spondyloarthropathies, like ankylosing spondylitis, psoriatic arthritis, or reactive arthritis. 

The autoimmune process underlying ankylosing spondylitis can lead to several other extra-articular manifestations. These include anterior uveitis, which involves the inflammation of the front eye chamber with the iris and ciliary body. Other important manifestations include inflammatory bowel disease, pulmonary fibrosis, acute leukemia, cardiac conduction disturbances, and aortitis, which can potentially lead to aortic aneurysm and dissection. 

Additionally, the physical examination will reveal tenderness to palpation over the sacroiliac joints. Some individuals might also have a limited range of motion of the lumbar spine; as well as findings like tenderness consistent with enthesitis.

If your patient presents with these findings, you should suspect ankylosing spondylitis!

Next, order labs, including inflammatory markers, like ESR and CRP, as well as rheumatoid factor and antinuclear antibodies. Next, don’t forget to check whether or not your patient has positive Human Leukocyte Antigen or HLA-B27 antigen, which is highly associated with ankylosing spondylitis! Finally, as far as imaging goes, obtain an X-ray of the lumbar spine and bilateral sacroiliac joints, and consider an MRI. 

Now, here’s a clinical pearl! The laboratory workup for inflammatory arthritis can be quite extensive. You may need additional labs, such as c-ANCA and p-ANCA, anti-cyclic citrullinated peptide, and uric acid. Additionally, you might need to check Lyme disease serologies, complement levels, and joint fluid analysis. These tests can help you rule out other rheumatologic conditions because they’re typically normal in individuals with ankylosing spondylitis!

Individuals with ankylosing spondyloarthritis will have elevated inflammatory markers and rheumatoid factor and antinuclear antibodies will be negative! In most cases, HLA-B27 will be positive, but sometimes the test might come back negative.

Finally, imaging will reveal a bilateral, symmetrical erosive arthropathy characterized by joint erosions and sclerosis classically at the sacroiliac joints. In severe cases, there might be multiple syndesmophytes between vertebrae, often referred to as bamboo spine.

In cases where X-ray findings are normal or unclear, but the clinical suspicion for ankylosing spondylitis is still high, consider an MRI. 

MRI picks up signs of inflammatory change, which allows detection of classic findings such as sacroiliitis, or inflammation at the vertebral body corners also known as  ‘shiny corners’.