Variables analyzed in the derivation cohort for sacroiliitis (12 AS and 12 control patients). Patients with ankylosis were not analyzed for erosive, sclerotic, or degenerative changes.
| Variables | AS/control, n | Sn (95% CI) | Sp (95% CI) | LR+ (95% CI) | LR− (95% CI) |
|---|---|---|---|---|---|
| Ankylosis | 5/0 | 42 (15–72) | 100 (74–100) | ∞ | 0.6 (0.4–0.9) |
| Among patients without ankylosis, 7 AS and 12 control patients | |||||
| Sensitivity analysis | |||||
| Any iliac erosions | 7/5 | 100 (59–100) | 58 (28–85) | 2.4 (1.2–4.7) | 0 |
| Any sacral erosions | 7/1 | 100 (59–100) | 92 (62–100) | 12.0 (1.8–78) | 0 |
| ≥ 1 erosion transverse | 7/4 | 100 (59–100) | 67 (35–90) | 3.0 (1.4–6.7) | 0 |
| ≥ 1 erosion coronal | 7/6 | 100 (59–100) | 50 (21–79) | 2.0 (1.1–3.5) | 0 |
| ≥ 1 large erosion transverse | 5/1 | 71 (29–96) | 92 (62–100) | 8.6 (1.2–59) | 0.3 (0.1–1.0) |
| ≥ 1 large erosion coronal | 6/2 | 86 (42–100) | 83 (52–98) | 5.1 (1.4–19) | 0.2 (0.03–1.0) |
| Total erosion score | |||||
| ≥ 1 erosion | 7/6 | 100 (59–100) | 50 (21–79) | 2.0 (1.1–3.5) | 0 |
| ≥ 3 erosions | 7/0 | 100 (59–100) | 100 (74–100) | ∞ | 0 |
| ≥ 5 erosions | 6/0 | 86 (42–100) | 100 (74–100) | ∞ | 0.1 (0.02–0.9) |
| Sclerosis | |||||
| Iliac depth > 0.3 cm | 6/7 | 86 (42–100) | 42 (15–72) | 1.5 (0.8–2.6) | 0.3 (0.05–2.4) |
| Iliac depth > 0.5 cm | 2/4 | 29 (4–71) | 67 (35–90) | 0.9 (0.2–3.5) | 1.1 (0.6–2.0) |
| Sacral depth > 0.3 cm | 2/3 | 29 (4–71) | 75 (43–95) | 1.1 (0.3–5.3) | 1.0 (0.5–1.7) |
| Sacral depth > 0.5 cm | 1/1 | 14 (0.4–58) | 92 (62–100) | 1.7 (0.1–23) | 0.9 (0.7–1.3) |
AS: ankylosing spondylitis; Sn: sensitivity; Sp: specificity; LR: likelihood ratio.