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Table 2 Features of AS/Spondylitis Sacroiliitis and Disease Mimics

From: Sacroiliitis mimics: a case report and review of the literature

  Spondylitis & AS Paget Disease of bone DISH Osteitis Condensans Ilii Sarcoidosis Brucella & other infections
Pelvic Radiographic findings -Symmetric, bilateral changes (AS)
-unilateral changes more common with other spondylitis
-primarily inferior (synovial) part of the joint
-erosions present
-ankylosis at end stage
-iliac wing, iliopectineal and ischiopubic lines: cortical thickening and sclerosis
-lytic & sclerotic lesions
-mostly asymmetric presentation
-primarily superior (ligamentous) joint area
-appearance of “ankylosis”
-triangle of sclerosis in the ilium adjacent to the inferior SI joint
-often bilateral
-no erosions
-normal joint space (no narrowing)
-mostly unilateral, but can be bilateral
-sclerosis and irregularities of sacroiliac joints margins
-may involve synovial or cartilaginous parts, dependent on if boney or joint granulomatous infiltration
-no Xray changes until about 15 days of infection
-extensive erosions
-subsequent boney repair (may involve more than the anterior-inferior part) which may progress to ankylosis
Extra-pelvic radiographic lesions -continuous spine involvement (no skip lesions)
-shiny corner on vertebra bodies involved; squaring of vertebral bodies
-skull and long bones are commonly involved -Skip lesions in the spine
-bulky osteophytic bridging and ossification
-“flowing” ALL ossification
-all spinal segments, but typically thoracic
-extra-spinal entheseal ossification, periarticular hyperostosis of the hands, knees, and elbows and quadriceps tendon
-none -Often hilar lymphadenopathy, infiltrates on CXR
-osseous findings such as reticular “lacy” pattern in phalanges
-Dependent on infectious localization
Genetic Association HLA-B27 HLA-DR2, SQSTM1 gene Possibly some SNPs in COL6A1 No HLA association BTNL2 gene HLA-B39 (Brucellosis)
Age at onset, Gender <40 years old, likely equal sexes >40 years old >50 years old Middle-age, predominantly multiparous females <40 years old Middle-age Any age (typically young adults and children)
  1. As depicted here, there are some features in the pelvic radiographic findings which help distinguish among sacroiliitis mimics. There is also heavy reliance on extra-pelvic radiographic lesions