Ankylosing spondylitis vs Reactive, psoriatic, and enteropathic arthritis
How to tell Ankylosing spondylitis and Reactive, psoriatic, and enteropathic arthritis apart when a board question makes them look alike.
AS is axial sacroiliitis; reactive follows infection; psoriatic has psoriasis/nails/dactylitis; enteropathic follows IBD activity.
Side by side
Ankylosing spondylitis causes inflammatory back pain, morning stiffness, sacroiliitis, reduced spine mobility, uveitis, HLA-B27 association, and bamboo spine in advanced disease.
Reactive arthritis follows GI/GU infection; psoriatic arthritis has psoriasis, nail pitting, dactylitis, and DIP disease; enteropathic arthritis tracks inflammatory bowel disease.
Enthesitis and axial inflammation drive sacroiliac and spinal fusion patterns.
Seronegative spondyloarthritides share enthesitis but differ by trigger infection, skin/nail disease, or bowel inflammation.
Bilateral sacroiliitis, HLA-B27, limited chest expansion, and bamboo spine support ankylosing spondylitis.
Urethritis/conjunctivitis/arthritis supports reactive; nail pitting supports psoriatic; Crohn or UC flares support enteropathic arthritis.
The trap
All are seronegative and HLA-B27 linked, so axial pattern, trigger, skin, nails, and bowel disease separate them.
The repair move
For seronegative spondyloarthritis, anchor on axial spine, recent infection, psoriasis/nails, or bowel disease.
Try a free question
CoreA 28-year-old man has 1 year of low back pain and stiffness that is worse in the morning, lasts >60 minutes, and improves with exercise. He has had one episode of anterior uveitis. Exam shows reduced lumbar flexion (Schober test <5 cm) and reduced chest expansion. Pelvic x-ray shows bilateral symmetric sacroiliitis. HLA-B27 is positive. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Ankylosing spondylitis. Ankylosing spondylitis is axial inflammatory arthritis with inflammatory back pain (>30 min morning stiffness, improves with exercise), bilateral sacroiliitis, HLA-B27 positivity, and extra-articular features (uveitis, aortitis, restrictive lung disease).
Why the other choices are tempting
- B. Reactive arthritis is asymmetric peripheral arthritis after GI/GU infection with the conjunctivitis-urethritis-arthritis triad.
- C. Psoriatic arthritis has psoriasis, nail pitting, dactylitis, and DIP arthritis.
- D. Enteropathic arthritis is associated with active IBD flares (UC or Crohn).
- E. Mechanical low back pain is non-inflammatory, worse with activity and improves with rest, without sacroiliitis on imaging.
Flashcards
Tap a card to flip it.
What joint pattern supports ankylosing spondylitis?
Bilateral sacroiliitis and inflammatory back pain support ankylosing spondylitis.
What clue supports psoriatic arthritis?
Nail pitting, dactylitis, or DIP arthritis supports psoriatic arthritis.
Quick answers
What is the fastest way to tell Ankylosing spondylitis from Reactive, psoriatic, and enteropathic arthritis?
AS is axial sacroiliitis; reactive follows infection; psoriatic has psoriasis/nails/dactylitis; enteropathic follows IBD activity.
What is the key clue for Ankylosing spondylitis?
Ankylosing spondylitis causes inflammatory back pain, morning stiffness, sacroiliitis, reduced spine mobility, uveitis, HLA-B27 association, and bamboo spine in advanced disease.
What is the key clue for Reactive, psoriatic, and enteropathic arthritis?
Reactive arthritis follows GI/GU infection; psoriatic arthritis has psoriasis, nail pitting, dactylitis, and DIP disease; enteropathic arthritis tracks inflammatory bowel disease.
What is the common trap with Ankylosing spondylitis vs Reactive, psoriatic, and enteropathic arthritis?
All are seronegative and HLA-B27 linked, so axial pattern, trigger, skin, nails, and bowel disease separate them.