A 38-year-old man, with recurrent inflammatory back pain and alternating buttock pain for 2 years. No extra-articular manifestations nor family history suggestive of spondyloarthritis, moderately raised C-reactive protein (CRP) (37 mg/L, reference range <5 mg/L) and erythrocyte sedimentation rate (ESR) (33 mm/first hour). HLA B27 negative. Pelvic radiography shows minimal sclerosis and irregularities of the inferior part of the sacroiliac joints, especially on the right side (arrow), resulting in an 'equivocal finding', that is, insufficient confidence in a diagnosis of sacroiliitis.