Background Although there are no consensus on how to define spinal involvement in axial psoriatic artritis (axPsA), our data suggest that the presence of spinal symptoms (defined as a combination of inflammatory back pain plus back stiffness) can be sufficient. However x-ray evaluation of sacroiliac joints may be normal at the first stage of the disease.
Objectives To evaluate the negative predictive value of sacroiliac x-rays versus MRI to rule out the diagnosis of sacroiliitis in peripheral PsA.
Methods Cross sectional descriptive and observational study of PsA patients classified according to CASPAR criteria. All patients had peripheral arthritis not spinal back pain and normal or grade I sacroiliac involvement determined by x-rays. All patients were evaluated according to current standard care. HLA-B27 was determined in all patients. Sacroiliac MRI was performed with either a Tesla 1.5 Gyroscan Intera (Philips MS) or Tesla 1.5 Signa-Excite with the following coronal sequences T1-TSE, T2-TGE and STIR with slices of 4mm of thickness, criteria for lesions were as ASAS proposal. The negative predictive value of x-rays versus MRI was determined as well as the 95% CI. Patients’ characteristics were compared according to MRI results, by means of Mann-Whitney U test, chi-squared test and Fisher’s exact test.
Results Sacroiliac MRI was performed in 59 patients from a total of 97 PsA patients with peripheral arthritis. There were not significant differences in both groups of patients. MRI patients had a medium age of 49,2±12,9 years, a time of evolution of the disease of 9,4±7,6 years. 96,4% patients had a normal sacroiliac x-rays, 2 had grade I unilateral and bilateral sacroiliitis respectively. HLA-B27 was negative in 93,2% (n=55) patients. 20,3% (n=12) showed active inflammatory lesions (1 with x-rays grade I bilateral). All patients were HLA-B27 negative. There were not significant clinical differences between MRI positive/negative patients, the exception was the occiput to wall distance (p=0,032). The negative predictive value of sacroiliac x-rays versus sacroiliac MRI was of 79,7% (95%IC: 68,5%–90,8%)
Conclusions Conventional x-rays versus MRI for the evaluation of sacroiliitis had a negative predictive value of 79,7%. In this study the sacroiliac involvement in PsA does not depend on the presence of spinal pain, HLA-B27 or radiological sacroiliitis.
Funded with a grant from: Instituto de Salud Carlos III, FIS PI080789
Disclosure of Interest None Declared