Background/Purpose:

The recent Assessment of SpondyloArthritis international Society (ASAS) classification criteria proposed the concept of axial spondylarthritis (axSpA) to enable earlier treatment not only for patients fulfilling the modified New York (mNY) criteria for ankylosing spondylitis (AS), but also  for patients with non-radiographic axSpA (nr-axSpA).  There is uncertainty whether the benefit of anti-TNF therapy in patients with nr-axSpA is as impressive as in patients with established AS, especially when the ASAS criteria and therapeutic recommendations are applied in real clinical practice.

Methods: Our aim was to compare the baseline characteristics and one year clinical outcome of anti-TNF therapy in axSpa patients prospectively followed in a large academic rheumatology center.  This was a single center study conducted within the national biologics registry. To get reimbursement for anti-TNF therapy, all AS patients had to have high baseline disease activity (defined as BASDAI >4, and CRP > 10 mg/l).  ASAS classification criteria were applied retrospectively using the data recorded in the source clinical documentation. All patients with inflammatory back pain fulfilling either ASAS criteria for nr-axSpA, or mNY criteria for AS starting treatment with anti-TNF therapy were included in the analysis.

Results:  At baseline, patients with nr-axSpa had shorter disease duration, higher number of swollen peripheral joints, and were more often treated with glucocorticoids and synthetic DMARDs. There were no statistical significant differences in the effect of biologics on the improvement in BASDAI, BASFI, EUROQOL and spinal pain during first 12 months of treatment. Also, the QALY area under the curve was no different between both groups. There was significantly larger improvement in CRP in the group of AS patients, while in the nr-axSpA group there was greater change in the improvement of SJ, but these differences in range of change appeared to be caused by the ceiling effect of uneven baseline values of these measures.

Conclusion: Although there were some important baseline differences between both cohorts, the amount of improvement in axial symptoms, physical function and quality of life   during the first 12 months of the anti-TNF treatment was similar in nr-axSpA and AS patients.

Acknowledgements: This work was supported by project of MHCR for conceptual development of research organization 023728

Table: Baseline characteristics and outcome of 12 months of anti-TNF therapy in AS and nr-axSpA patients

		AS (N=275)	nr-axSpA(N=39)	p-value
Female	n (%)	68 (24.7 %)	15 (38.5 %)	0.069
Age (years) at baseline	mean (SD)	38.0 (10.4)	37.9 (12.2)	0.713
HLA B27 positivity	n (%)	252 (92.0 %)	32 (84.2 %)	0.117
Disease duration prior to start of anti-TNF therapy of anti-TNF therapy (years)	mean (SD)	9.0 (8.6)	4.9 (6.3)	<0.001
Peripheral joint involvement ever	n (%)	94 (34.3 %)	24 (64.9 %)	<0.001
Concomitant glucocorticoids  at baseline	n (%)	23 (8.4 %)	11 (28.2 %)	<0.001
Concomitant DMARD at baseline	n (%)	57 (20.7 %)	21 (53.8 %)	<0.001
CRP (mg/l) at baseline	mean (SD)	25.5 (21.2)	21.9 (30.1)	0.013
CRP (mg/l) at 12 months	mean (SD)	5.3 (8.2)	4.8 (8.9)	0.232
CRP  (mg/l) change per year	mean (SD)	-19.9 (22.2)	-17.3 (30.3)	0.013
BASDAI at baseline	mean(SD)	6.1 (1.9)	5.8 (2.5)	0.841
BASDAI at 12 months	mean (SD)	2.1 (1.7)	1.8 (1.5)	0.256
BASDAI change per year	mean (SD)	-4.1 (2.3)	-4.2 (2.8)	0.909
BASFI at baseline	mean (SD)	4.9 (2.2)	4.1 (2.7)	0.115
BASFI at 12 months	mean (SD)	2.6 (2.1)	1.4 (1.2)	0.002
BASFI change per year	mean (SD)	-2.3 (2.1)	-2.7 (2.7)	0.607
HAQ at baseline	mean (SD)	0.9 (0.5)	0.8 (0.6)	0.449
HAQ at 12 months	mean (SD)	0.5 (0.5)	0.4 (0.3)	0.636
HAQ change per year	mean (SD)	-0.4 (0.5)	-0.5 (0.5)	0.719
Spinal pain (BASDAI Q2 0-100) at baseline	mean (SD)	70.5(22.1)	63.5(27.4)	0.256
Spinal pain (BASDAI Q2 0-100) at 12 months	mean (SD)	27.9 (22.4)	24.0 (20.5)	0.392
Spinal pain (BASDAI Q2 0-100) change per year	mean (SD)	-44.9 (28.0)	-40.0 (33.8)	0.414
Number of swollen joints/44 at baseline	mean  (SD)	1.8 (3,4)	3.4 (4.8)	0.002
Number of swollen joints/44 at 12 months	mean (SD)	0.3 (1.2)	1.1 (2.5)	0.002
Number of swollen joints/44 change per year	mean (SD)	-1.3 (3.0)	-2.6 (4.8)	0.055
EUROQOL	mean (SD)	0.4 (0.3)	0.4 (0.3)	0.699
EUROQOL	mean (SD)	0.8 (0.2)	0.7 (0.2)	0.462
QALY EQ-5D (area under the curve)	mean (SD)	0.7 (0.2)	0.7 (0.1)	0.525
Mann-Whitney U test, Pearson Chi-Square test (or Fisher exact test when frequencies are low) and Gamma test were used when comparing continuous, nominal and ordinal variables, respectively.

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