Ankylosing spondylitis vs Mechanical back pain
How to tell Ankylosing spondylitis and Mechanical back pain apart when a board question makes them look alike.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
Improvement with exercise and worsening with rest separates inflammatory axial disease from mechanical pain.
Side by side
Inflammatory back pain in a patient younger than 45 years, morning stiffness over 30 minutes, and improvement with activity suggests ankylosing spondylitis.
Pain provoked by lifting or prolonged standing that worsens with activity and improves with rest supports mechanical back pain.
Axial spondyloarthritis causes sacroiliac inflammation and progressive spinal enthesitis.
Muscle, ligament, or disc strain creates nociceptive pain without persistent inflammatory sacroiliac disease.
Inflammatory markers may be elevated, HLA-B27 can be present, and pelvic imaging shows bilateral sacroiliitis with erosions or marrow edema on MRI when radiographs are normal early.
Mechanical pain has normal ESR and CRP, no sacroiliitis on imaging, and neurologic exam is usually normal unless focal nerve root compression exists.
The trap
A frequent miss is ordering lumbar MRI for disc disease first in a young patient with classic inflammatory pattern. The resolving clue is sacroiliac involvement, so SI joint imaging is the key test.
The repair move
Next best step: obtain sacroiliac imaging, usually plain radiographs first and MRI if radiographs are nondiagnostic, then start full-dose NSAID therapy such as naproxen 500 mg twice daily plus exercise-based physical therapy. Escalate to TNF-alpha or IL-17 inhibitor if symptoms remain active after NSAID trial.
Try a free question
CoreA 29-year-old man has chronic low back pain for 7 months, morning stiffness for 1 hour, and improvement with exercise. ESR is elevated. What is the most likely diagnosis?
Show answer and explanation
Answer: A. Ankylosing spondylitis. Inflammatory back pain pattern with prolonged stiffness and activity improvement is classic for ankylosing spondylitis.
Why the other choices are tempting
- B. Mechanical pain typically worsens with activity and improves with rest.
- C. Cauda equina syndrome would include severe neurologic deficits such as urinary retention or saddle anesthesia.
- D. Compression fracture usually has acute focal pain after trauma or osteoporosis risk.
- E. Metastatic disease generally presents with progressive constant pain and red-flag systemic findings.
Flashcards
Tap a card to flip it.
What pain behavior pattern favors ankylosing spondylitis over mechanical back strain?
Inflammatory pain improves with movement and worsens with rest, often with prolonged morning stiffness.
Which anatomic site should be imaged first when axial spondyloarthritis is suspected?
The sacroiliac joints, not only the lumbar spine.
Quick answers
What is the fastest way to tell Ankylosing spondylitis from Mechanical back pain?
Improvement with exercise and worsening with rest separates inflammatory axial disease from mechanical pain.
What is the key clue for Ankylosing spondylitis?
Inflammatory back pain in a patient younger than 45 years, morning stiffness over 30 minutes, and improvement with activity suggests ankylosing spondylitis.
What is the key clue for Mechanical back pain?
Pain provoked by lifting or prolonged standing that worsens with activity and improves with rest supports mechanical back pain.
What is the common trap with Ankylosing spondylitis vs Mechanical back pain?
A frequent miss is ordering lumbar MRI for disc disease first in a young patient with classic inflammatory pattern. The resolving clue is sacroiliac involvement, so SI joint imaging is the key test.