Sensitivity, specificity, and likelihood ratio (LR) of scintigraphy imaging for the diagnosis of axial spondyloarthritis (SpA). Scintigraphy examinations of the sacroiliac joints were performed in 207 patients. Of them, 97 patients were classified with axial SpA, 13 patients with suspicion for axial SpA, and 97 as controls.
| Diagnosis | Unilateral or Bilateral Sacroiliitis, or Both | Sensitivity, % | Specificity, % | LR |
|---|---|---|---|---|
| Group A (total group): axial SpA (AS plus Nonradiographic axial SpA, n = 97)* | Any | 64.9 | 50.5 | 1.3 |
| Bilateral | 40.2 | 57.7 | 1.0 | |
| Unilateral | 24.7 | 92.8 | 3.4 | |
| Group A1: AS (n = 56) | Any | 67.9 | 50.5 | 1.4 |
| Bilateral | 42.9 | 57.7 | 1.0 | |
| Unilateral | 25.0 | 92.8 | 3.5 | |
| Group A1a: AS subgroup, grade 2/3 sacroiliitis (n = 43)** | Any | 74.4 | 50.5 | 1.5 |
| Bilateral | 46.5 | 57.7 | 1.1 | |
| Unilateral | 27.9 | 92.8 | 3.9 | |
| Group A1b: AS subgroup, grade 4 sacroiliitis (n = 8)** | Any | 12.5 | 50.5 | 0.3 |
| Bilateral | 12.5 | 57.7 | 0.3 | |
| Unilateral | 0 | 92.8 | 0 | |
| Group A2: Nonradiographic axial SpA (n = 41) | Any | 61.0 | 50.5 | 1.2 |
| Bilateral | 36.6 | 57.7 | 0.9 | |
| Unilateral | 24.4 | 92.8 | 3.4 | |
| Group B: Axial SpA (AS plus nonradiographic axial SpA, n = 47), only quantitative sacroiliitis*** | Any | 74.5 | 27.1 | 1.0 |
| Bilateral | 46.8 | 41.7 | 0.8 | |
| Unilateral | 27.7 | 85.4 | 1.9 |
↵* Group A consists of all patients with axial SpA (pooled data) including 56 patients with AS (Group A1) and 41 patients with nonradiographic axial SpA (Group A2).
↵** Group A1 consists of all patients with AS according to the modified New York criteria, including patients with sacroiliitis grade 2/3 on conventional radiography (Group A1a) and patients with total ankylosis on conventional radiography (Group A1b). In 5 patients with AS, the exact grading of sacroiliitis was missing.
↵*** Subgroup of patients with axial SpA, in whom absolute values of the sacroiliac joint sacrum index were given (26 patients with AS, 21 patients with nonradiographic axial SpA, and 48 controls).