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Background: Sclerosis in the sacroiliac joints (SIJ) on radiography and computed tomography (CT) is common but widely considered a non-specific finding of sacroiliitis due to an association with degeneration and osteitis condensans ilii, despite little formal study. Availability of low dose radiation CT may lead to more widespread use for diagnostic evaluation.
Objectives: We standardized the definition of sclerosis on CT and then aimed to determine whether this lesion could be reliably detected and its diagnostic utility.
Methods: 215 CT scans were obtained from patients with a history of low back pain. 107 patients had a clinical diagnosis of spondyloarthritis (SpA) and 108 patients were clinically proven not to have SpA. Groups were age and gender matched (140 males, 75 females, mean age was 45 years). Three musculoskeletal radiologists, blinded to patient demographics and diagnosis, scored the CTs after standardization of lesion definitions and calibration. Erosions, sclerosis, and ankylosis were graded by size and number of articular surfaces/ joints involved. Sclerosis was considered definite if located along the cartilaginous compartment, measured >5mm in all 3 planes, and present >5mm from the joint surface. Discrepant scores were arbitrated and inter-reader reliability calculated by intra-class correlation coefficient (ICC). Diagnostic utility of CT lesions was determined by calculating sensitivity and specificity for the clinical diagnosis and by logistic regression.
Results: ICC for sclerosis and erosion for each articular surface ranged from 0.65–0.76 and 0.71–0.78, respectively. ICC for ankylosis was 0.87–0.89. Sclerosis occurred in 87 (81%) cases with SpA and 25 (23%) controls. For a single articular surface the specificity for sacroiliitis ranged between 88–94%, for any two articular surfaces 95–100%, for all 4 articular surfaces 100%. Sensitivity ranged from 14% (4 articular surfaces) to 55% (either ilium). Erosion and ankylosis had a similar specificity range of 91–100% and 92–93%. The odds ratio was 4.9 for presence of definite sclerosis, and 12.6 for bilateral joint involvement. The odds ratio increased to 84.2 for bilateral erosion and 22.8 for bilateral ankylosis.
Table 1
Sclerosis of articular surface (s) involved Specificity (95% CI) Sensitivity (95% CI) Single articular surface Either ilium: 87% (82–91) – 91% (87–95) Either ilium: 46% (39–52) - 51% (44–58) Either sacrum: 93% (89–96) – 94% (90 – 97) Either sacrum: 19% (14–25) - 21% (16–26) Any 2 articular surfaces 96% (94–99) – 99% (98–100) 10% (6–14) - 41% (35–48) All 4 articular surfaces 99% (8–100) 14% (9 – 19) Erosion of articular surface (s) involved Specificity (95% CI) Sensitivity (95% CI) Single articular surface Either ilium: 90% (85–94) Either ilium: 77% (71–83) Either sacrum: 94% (91–98) Either sacrum: 65% (58–72) Any 2 articular surfaces 96% (93–99) – 100% (100–100) 24% (18–31) – 67% (60–74) All 4 articular surfaces 100% (100–100) 38.1% (31–45) Ankylosis of articular surface (s) involved Specificity (95% CI) Sensitivity (95% CI) Single joint 92% (88 – 95) 60% (53–66) Both joints 93% (89 – 96) 58% (51–64)
Conclusions: When sclerosis measures >5mm in three planes and is located >5mm from a joint perimeter, it has high specificity for sacroiliitis, regardless of how many articular surfaces are involved, with similar specificity to erosion and ankylosis.
Disclosure of Interest: None declared
DOI: 10.1136/annrheumdis-2017-eular.6292