Structural progression in sacroiliac joints in patients with recent onset axial spondyloarthritis (AxSpA) was limited and occurred in very few patients over a 2-year period, according to French researchers.
The progression rate from nonradiographic AxSpA to radiographic AxSpA was less than 5% in a cohort of 449 patients with recent-onset disease, according to Maxime Dougados, MD, at Hôpitaux de Paris, France, and colleagues.
"Structural progression does exist but is quite small and only observed in a small number of patients," they wrote online in Arthritis & Rheumatology.
Moreover, the study suggested that genetic, environmental, and inflammatory factors were predictors of radiographic progression of the sacroiliac joints in early AxSpA.
The low rate of progression after 2 years of follow-up does not confirm the 10% rate of switching from nonradiographic AxSpA or radiographic AxSpA often cited in reviews, the authors noted.
Patients in the study were from the DESIR cohort, a multicenter French longitudinal register of patients with recent-onset inflammatory low back pain suggestive of AxSpA. Pelvic radiographs were collected at baseline and after 2 years of follow-up. These films were evaluated by two central readers, each of whom evaluated each sacroiliac joint according to the modified New York criteria, in which a grade of 0 is assigned for normal sacroiliac joints, 1 for suspicious changes, 2 for minimal abnormality, 3 for unequivocal abnormality, and 4 for severe abnormality.
Baseline and 2-year pelvic radiographs were available for 449 of the 708 patients enrolled. There were no significant differences in baseline characteristics between all enrolled patients and the evaluated patients.
Of the 326 patients who did not fulfill the modified NY criteria at baseline, 16 (4.9%) became positive after 2 years of follow-up. Over this same time, of the 123 patients that fulfilled the criteria at baseline, seven (5.7%) no longer fulfilled the criteria at year 2.
Other definitions of progression also were evaluated. For example, the change in the total sacroiliac joint score indicated that 20.9% had worsened while 12.7% had improvement in structural disease. A change of at least one grade in at least one sacroiliac joint occurred in 11.1% of progressors compared with 5.8% of regressors.
Evaluation of the changes in the mean total score of the two sacroiliac joints showed a minimal but statistically significant worsening of 0.1 (P<0.001) in the whole population. The magnitude of true progression was always higher for the subgroup of patients with baseline radiographic structural damage.
"It must be recognized that the rate of progression observed in the DESIR cohort was very low. For example, 300 of the 449 evaluated patients had no change at all in the total SIJ score," the authors wrote.
Despite several arguments in favor of the existence of a true progression, "it has to be recognized that the relative high number of 'regressors' makes the evaluation of the true rate of progression challenging. Our findings suggest that the progression seems to be a true phenomenon but also that the regression might reflect the measurement error of the measure," they suggested.
Three variables -- smoking status, HLAB27 positivity, the presence of inflammation on MRI of the sacroiliac joints -- were correlated with a switch from nonradiographic to radiographic AxSpA. The percentage of switchers from nonradiographic to radiographic AxSpA was 8.3% in smokers versus 3.2% in nonsmokers; 8% in those with HLAB27 positivity compared with 0% in those who were HLAB27-negative; and 17.3% in patients with baseline sacroiliac joint inflammation on MRI versus 0% in those without inflammation.
"In our study, the relation between the presence of inflammation on MRI and radiographic progression was very high, suggesting a very low risk of radiographic structural progression in case of the absence of subchondral bone edema observed on MRI of the sacroiliac joints," the authors stated.
When defining radiographic progression as a worsening of at least one grade in at least one sacroiliac joint, HLAB27 positivity, MRI positivity, and the presence of baseline structural damage at the sacroiliac joints on pelvic radiographs were factors associated with progression.
The study failed to show a clear relationship between an abnormal C-reactive protein level at baseline and radiologic progression.
A study limitation was the relative number of missing values (259 of the original 708 patients).
"The findings observed after 2 years of follow-up in the DESIR cohort require additional studies with a longer follow up period and also in other sets of patients in order to confirm these findings," the authors wrote, adding that their results should serve as the basis for translational research studies in order to understand the underlying mechanisms.
The DESIR cohort was sponsored by the Département de la Recherche Clinique et du Développement de l'Assistance Publique-Hôpitaux de Paris. An unrestricted grant from Pfizer was allocated for the 10 years of the follow-up of the recruited patients.
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