Background/Purpose:
Sustained clinical remission is one of the key benchmarks for treatment of AS
over the long term. We aimed to determine the factors predictive of sustained
clinical remission on anti-tumor necrosis factor
alpha (anti-TNFα) therapy and the
role of MRI parameters of inflammation and structural damage at baseline and
after treatment.

Methods:
In the FOllow-up Research Cohort in AS (FORCAST), AS
patients from Northern Alberta attending community and academic practices are
assessed for clinical and laboratory outcomes every 6 months, radiography at
baseline and 2 years, MRI at baseline, at 3-6
months for patients starting anti-TNFα,
and annually. MRI inflammation was assessed using Spondyloarthritis
Research Consortium of Canada (SPARCC) Sacroiliac Joint (SIJ) and 23-DVU Spine
scores while structural change was assessed independently using the SPARCC SIJ Structural
Scores (SSS) for fat metaplasia, erosion, backfill, ankylosis
and the Fat Ankylosing Spondylitis Spine Score (FASSS)
score for fat metaplasia. Sustained clinical remission was defined as
ASDAS<1.3 at two consecutive 6-monthly visits. We used univariate
and multivariate logistic regression to assess patient demographics, smoking,
B27, NSAID utilization, and baseline CRP, ASDAS, mSASSS,
SPARCC scores, SSS, and FASSS scores, adjusted for duration of follow up. We
also assessed attainment post-treatment of CRP<6mg/L, ASDAS<1.3, and
SPARCC MRI remission (SIJ <2 and spine <3) as predictors of future
remission.

Results: We assessed 316 patients on anti-TNF
therapy of mean (SD) age 41.2 (12.3) years, 78% males, mean (SD)
symptom duration 18.7 (11.1) years, and mean (SD) duration of follow up of 1704
(961.4) days, of whom 144 had MRI evaluation. 98 (31.0%) achieved sustained ASDAS remission after
mean (SD) follow up of 848.3 (682.4) days. In univariate
analyses, patients attaining ASDAS remission were younger (p<0.0001), had shorter
disease duration (p<0.0001), lower baseline ASDAS (p=0.01), were not current
smokers (p=0.01), had definite SIJ erosion (p=0.01) but low spinal fat
metaplasia (FASSS<5) (p=0.01) and SIJ ankylosis
scores (p=0.01), and post-treatment scores indicating SPARCC MRI remission of inflammation
(p=0.02), and normalised CRP (p=0.01). In multivariate analyses adjusted for
duration of follow up, age, current smoking, baseline ASDAS, and normalized CRP
were the strongest clinical predictors. The best models (in terms of R–squared values) included
age, sex, ASDAS, current smoker, duration of follow up, and an
MRI structural parameter (SSS erosion or ankylosis).

Conclusion: Current
smoking is negatively associated with attainment of sustained remission to
anti-TNF. Sustained remission is more likely in patients attaining normalised
CRP, in the presence of definite SIJ erosion, and in the absence of SIJ ankylosis.