SIJ findings
The SIJ analysis included 301 patients who had at least two sets of radiographs taken every 2 years over a 10-year follow-up period, 87 (28.9%) of whom had been treated with at least one TNF inhibitor during follow-up.
Radiographic SIJ progression was defined as the change in the sacroiliitis sum score over 2 years. Calculations considered both the current 2-year period and the previous 2-year period, as well as any use of TNF inhibitors or more than 12 months’ use.
There were no significant differences in sacroiliitis sum scores comparing people who were and were not treated with TNF inhibitors for at least 12 months in the current 2-year period. However, when the previous 2-year period was looked at there was a significant difference in the score between those who had and had not been treated for 12 or more months (0.15 vs. 0.27, respectively; P = .024).
“These data indicate that TNF inhibitors have a late effect,” Dr. Torgutalp said. “You cannot observe the effect of the TNF inhibitor on radiographic progression in the same interval, you have to wait to see this effect in the next interval,” he explained. That means that when a patient uses a TNF inhibitor, you must wait to see the effect on SIJ progression in the subsequent 2 years, he qualified.
Lessons for practice
“If we control inflammation, we might control structural damage progression,” Dr. Poddubnyy said.
If this is the case, then it is likely that other drugs that control inflammation in axSpA will have a similar effect, such as those that target interleukin-17 or Janus kinases. This is something in the future to look at in the GESPIC cohort once enough patient-years of data are available.
Early treatment is probably important, Dr. Poddubnyy suggested, “because in patients with early disease we can expect not that much structural damage at baseline.” Starting treatment early, at the inflammatory stage rather than at the stage where there was a lot of damage already there, could yield better results, he proposed.
“As a clinician, as a researcher, I would be really interested in demonstrating in a prospective, clinical trial that treating patients to target, achieving a remission, would be associated with retardation of structural damage progression. This has only been shown in observational studies so far, so this is an open question.”
Questions on adjustments made for confounding factors
Questions on the spinal presentation included whether there were any differences in NSAID use, to which Dr. Poddubnyy responded, “Patients on TNF inhibitors normally reduce NSAIDs. We adjusted, therefore, for NSAID use.”
The SIJ presentation garnered more questioning. Dr. Torgutalp qualified that both radiographic and nonradiographic patients had been included in the analysis, and “we observe the same effect.”
Asked how clinically relevant the findings were, he noted that, “to the best of our knowledge, this is the first data for sacroiliac joint progression.” The data for spinal progression seem to “reconcile the results from previous investigators,” where there had been some conflicting data on whether 2 or 4 years’ TNF-inhibitor therapy had any effect on radiographic progression.
“I don’t think you’ve adjusted for the baseline level of damage of the SIJ?” queried Pedro Machado, MD, of University College London Hospital. “As you know, in the spine, but also at the SIJ level, the baseline level of damage is usually one of the strongest predictors of further damage.”
This is not something that was adjusted for, Dr. Torgutalp conceded. “We will do it for further analysis,” he said.
Since 2010, GESPIC has been supported by grants from AbbVie. Dr. Poddubnyy reported financial relationships with AbbVie and numerous other pharmaceutical companies. Dr. Torgutalp had no relevant disclosures.