This document discusses sacroiliitis, which is inflammation of the sacroiliac joints located at the lower back. It lists common causes of sacroiliitis including diseases like ankylosing spondylitis, inflammatory bowel disease, and reactive arthritis. Sacroiliitis is usually bilateral and symmetrical for conditions like ankylosing spondylitis, but can be bilateral but asymmetrical for things like gout or psoriatic arthritis. Unilateral sacroiliitis may be caused by infection, tumors, or trauma. The document also describes the New York grading criteria for classifying sacroiliitis severity on x-rays from Grade 0 (normal) to Grade IV (complete fusion of the joint).

1. Sacroiliitis
Mohamed Ahmed Hefny, MD.

3. Usually bilateral and symmetrical
1. Enteropathic arthritis
• Crohn disease
• Ulcerative colitis
2. Ankylosing spondylitis
3. Rheumatoid Arthritis
4. Hyperparathyroidism: not a true sacroiliitis but can mimic
appearances
5. Osteitis condensans ilii
6. Multicentric reticulohistiocytosis
7. Whipple disease

4. Usually bilateral but asymmetrical
1. Gout
2. Psoriatic arthritis
3. Reactive arthritis (Reiter syndrome)
4. Osteoarthritis
5. Relapsing polychondritis
6. Behcet disease
7. Sacroiliitis circumscripta

5. Usually unilateral
1. Neoplastic destructive process
2. Infective
• pyogenic septic arthritis
• tuberculous sacroiliitis
• brucellosis
3. Paraplegia
4. SAPHO syndrome

6. Causes of sacroiliitis - symmetric vs asymmetric (mnemonic)
PAIR
Mnemonic
P: psoriatic arthritis
A: ankylosing spondylitis
I: inflammatory bowel disease related
R: reactive (e.g. Reiter syndrome)
P & R (letters are far apart) are the asymmetric causes and the inside
letters A & I (letters are close together) are the symmetric causes.

7. Sacroiliitis grading (New York criteria)
Sacroiliitis grading can be achieved using plain radiographs according to
the New York criteria.
1. Grade 0: normal
2. Grade I: some blurring of the joint margins - suspicious
3. Grade II: minimal sclerosis with some erosion
4. Grade III
• definite sclerosis on both sides of joint
• severe erosions with widening of joint space with or without
ankylosis
5. Grade IV: complete ankylosis

8. Grade 0: normal
Grade I: some blurring of the joint
margins - suspicious

9. Grade III
• definite sclerosis on both sides of joint
• severe erosions with widening of joint space with or without

10. Grade IV: complete ankylosis

11. Grade 1 (a) sacroiliitis was defined as focal erosions seen on
only one of either semicoronal or axial images.
Grade 2 (b) sacroiliitis was defined as erosions seen on 25 %
of consecutive semicoronal or axial images.
Grade 3 (c, d) sacroiliitis included bony erosions on C25 % of
consecutive semicoronal or axial images, or joint space
alteration, or partial ankylosis