A 25 year old female is referred for evaluation of back pain.  She has had chronic back pain since high school and thought it was related to injuries since she was active in numerous sports,.  During college, she was less physically active in sports, but the back pain persisted.  She describes her back stiffness as most severe in the morning upon awakening and after prolonged inactivity, such as sitting in the classroom for an hour.  The symptoms last at least for 60 minutes and improve if she stretches, moves, or participates in physical exercise.  Her pain is mostly in the lower thoracic region and she describes muscle spasms.  She will awaken at night after 3-4 hours of sleep with back pain and will have to walk around.  Occasionally, she will have alternating buttock pain as well.  Naproxen OTC reduces her stiffness but she is afraid to take them regularly due to concern for toxicity.

• Past Medical History: None
• Family and Social History: Unmarried elementary school teacher.  No family history of back pain; brother with psoriasis
• Medications:  None
• Review of Systems:  One episode of iritis in college that resolved with topical steroid eye drops
• General Physical Exam: Vital signs stable.  HEENT normal; skin without lesions; pulmonary, cardiac, GI and neurologic exams are all normal
• Musculoskeletal Exam:  Cervical spine with normal range of motion.  No evidence of peripheral arthritis or enthesitis; no point tenderness in thoracic or lumbar regions. There is loss of lumbar lordosis and the Schober's exam is 10 to 13 cm on full flexion (normal is >15 cm on full flexion)

What are the typical features of inflammatory back pain?

The characteristics features of inflammatory back pain include: 

1. Onset of back pain before age 40
2. Insidious in onset
3. Pain that improves with exercise but no improvement with rest
4. Nocturnal pain, especially the second half of the night

What are other commonly associated features in this diagnosis that should be sought?

Aside from inflammatory back pain, other manifestations include: enthesitis, particularly in the Achilles tendon, plantar fascia, anterior chest wall or iliac crest; shoulder or hip joint involvement; uveitis; aortitis; IgA nephropathy; rarely neurologic involvement; and apical pulmonary fibrosis.  

What is the best approach to classify and confirm the diagnosis?

Aside from the history and physical exam, laboratory data has limited utility. Although elevations in inflammatory markers such as erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) are often present, these are nonspecific.  Radiographic imaging in early disease can be normal but obtaining sacroiliac (SI) joint, thoracic and lumbar spine films can sometimes reveal characteristic changes (enthesitis at the vertebral body, syndesmophytes, sacroiliac erosions or sclerosis) if symptoms have been of longer duration. MRI with STIR images of the axial spine and SI joints are more sensitive for early inflammatory changes and bone marrow edema.  HLA B27 testing is helpful in supporting the diagnosis in a patient with classic inflammatory back symptoms or other associated features (arthritis, dactylitis, heel enthesitis, uveitis, psoriasis, inflammatory bowel disease, elevated inflammatory markers, response to NSAIDs, or family history of spondyloarthropathy (SpA)  if radiographic changes are not yet present.

Spondyloarthropathy encompasses a group of diseases:  ankylosing spondylitis, non-radiographic axial SpA, undifferentiated SpA, reactive arthritis, SpA associated with psoriasis, inflammatory bowel disease, and juvenile onset SpA.

Another classification proposed by the Assessment of Spondyloarthritis International Society (ASAS) separates this group of diseases into two main clinical classifications: predominantly axial spondyloarthritis or predominantly peripheral spondyloarthritis.

Thus, in this case, the patient would have axial spondyloarthritis or ankylosing spondylitis if there were radiographic changes, or non-radiographic axial SpA if her films Xrays were normal.