The clinical presentation is consistent with ankylosing spondylitis (AS). The best initial diagnostic test is a radiograph of the sacroiliac joint.
AS is a seronegative spondyloarthropathy that commonly causes chronic inflammatory disease in the spine and sacroiliac joints. Typically, this spondyloarthropathy affects young adults who are male. AS involves the spine and sacroiliac joints, hips, shoulders, entheses, peripheral joints, as well as having extra-articular manifestations (i.e., uveitis, inflammatory bowel disease, aortic insufficiency). Radiographic findings include symmetric sacroilitis, ankyloses, and sacroiliac joint fusion. There is a strong correlation between HLA B-27 and AS, and HLA-testing is warranted in an individual with imaging suggestive of AS. Nonsteroidal anti-inflammatory drugs (NSAIDs) can provide substantial relief to inflammatory back pain. NSAIDs are considered first-line in the pharmacologic treatment of AS. If patients are unresponsive to NSAIDs, sulfasalazine can then be used.
In order to answer this question, you must first recognize that this young male is presenting with signs and symptoms consistent with AS, such as experiencing low back pain that improves with activity, as well as decreased expansion of the chest. Lower back stiffness can be assessed with decreased flexion on Schober's testing. The next diagnostic step is to obtain a radiograph of the sacroiliac joint. Radiography of the sacroiliac joint is the best initial test, and that MRI of that same area is the most accurate test.
Illustration A depicts the "bamboo spine" that can be seen in AS. This is the result of complete vertebral body fusion via syndesmophytes and ossification of related areas. Note that the sacroilitis on radiography is seen early in the disease process. This sacroilitis is considered a hallmark of AS. Radiography can confirm the diagnosis if the certain sacroilitis criteria are met.
Answer 1: Human leukocyte antigen (HLA) B-27 testing is not the best initial test. If the patient has a negative radiograph, and has some findings suggestive of a spondyloarthropathy, HLA-B27 testing should be pursued.
Answer 2: Erythrocyte sedimentation rate (ESR) is a nonspecific assessment of inflammation.
Answer 3: MRI of the sacroiliac joint is incorrect but may be pursued if radiography is inconclusive.
Answer 5: Slit-lamp examination is incorrect. Though it is true that extra-articular manifestations of AS include uveitis, it is important to diagnose the underlying disease process.
Ankylosing spondylitis, reactive arthritis, psoriatic arthritis, undifferentiated spondyloarthropathy, and inflammatory bowel disease-associated spondyloarthropathy are examples of diseases that fall under the umbrella term “spondyloarthropathies.” These diseases are associated with the HLA-B27 gene, as well as enthesitis. (1)
Kataria RK, Brent LH. Spondyloarthropathies. Am Fam Physician. 2004 Jun 15;69(12):2853-60. Review.
PMID:15222650 (Link to Abstract)