Can Disease Activity in Patients with Psoriatic Arthritis be Adequately Assessed By a Modified Disease Activity Index for Psoriatic Arthritis (DAPSA) Based on 28 Joints?

Brigitte Michelsen^1,2, Joseph Sexton¹, Josef S. Smolen³, Daniel Aletaha⁴, Niels Steen Krogh⁵, Désirée van der Heijde⁶, Tore Kvien⁷ and Merete Lund Hetland^8,9, ¹Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway, ²Division of Rheumatology, Department of Internal Medicine, Hospital of Southern Norway Trust, Kristiansand, Norway, ³Division of Rheumatology, Department of Medicine 3, Medical University of Vienna, Vienna, Austria, ⁴Medical University of Vienna, Vienna, Austria, ⁵ZiteLab ApS, Copenhagen, Denmark, ⁶Leiden University Medical Centre, Leiden, Netherlands, ⁷Dept. of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway, ⁸Copenhagen Center for Arthritis Research, Center for Rheumatology and Spine Diseases, The DANBIO Registry, Glostrup, Denmark, ⁹University of Copenhagen, Copenhagen, Denmark

Meeting: 2018 ACR/ARHP Annual Meeting

Keywords: outcome measures and psoriatic arthritis

Session Information

Date: Sunday, October 21, 2018

Title: Spondyloarthritis Including Psoriatic Arthritis – Clinical Poster I: Imaging, Clinical Studies, and Treatment

Session Type: ACR Poster Session A

Session Time: 9:00AM-11:00AM

Background/Purpose: Many registries routinely collect only 28 joint count, although 66/68 joint count has higher face validity in PsA. We aimed to compute and test the validity of a simplified Disease Activity index for PSoriatic Arthritis (DAPSA) using 28 instead of 66/68 joint count.

Methods: We included PsA patients from the Danish national quality registry DANBIO, divided into examination (n=3157 patients, 24160 visits) and validation cohorts (n=3154 patients, 24160 visits) according to odd/even IDs. We defined: DAPSA28 = (28TJC x conversion factor₁) + (28SJC x conversion factor₂) + patient global [0-10VAS] + pain [0-10VAS] + CRP [mg/dL]. Identification of conversion factors was performed by Generalized Estimating Equations in the examination cohort, and criterion, correlational and construct validity explored in the validation cohort.

Results: Mean (SD) age: 52.0 (13.8) years, 54.4% females. Conversion factor₁= 1.6, 95%CI (1.6-1.7), conversion factor₂= 1.6, 95%CI (1.5-1.6), leading to:

DAPSA28 = (28TJC + 28SJC) x 1.6 + patient global [0-10 VAS] + pain [0-10 VAS] + CRP [mg/dL]. Criterion validity: Physician’s global and DAPSA/DAPSA28 were similarly correlated (r=0.63/r=0.61, p<0.001). DAPSA/DAPSA28 had comparable discriminative power, expressed as standardized mean difference (DAPSA,0.90; DAPSA28,0.93) to distinguish between patients in high (starting bDMARD) and low (not starting/changing s/bDMARD for ≥60 days) disease activity. Agreement between DAPSA/DAPSA28 disease activity states was best for remission/low disease activity (Table).

	DAPSA(n=6421) n(%) stratified by DAPSA disease activity states
DAPSA28 (n=6421)		DAPSA≤4	DAPSA>4 and ≤14	DAPSA>14 and ≤28	DAPSA>28
	DAPSA28≤4	1135(98.4)	126(5.6)	4(0.2)	0(0)
	DAPSA28>4 and≤14	18(1.6)	2073(91.5)	345(17.8)	14(1.3)
	DAPSA28>14 and ≤28	0(0)	66(2.9)	1509(77.9)	248(23.3)
	DAPSA28>28	0(0)	0(0)	80(4.1)	803(75.4)

Kappa with quadratic weighting of DAPSA/DAPSA28 disease activity states was high; 0.92 95%CI (0.92-0.92). Standardized response means for DAPSA/DAPSA28 were -0.96/-0.92 (n=572) for visits after bDMARD start. Correlational validity: Baseline DAPSA/DAPSA28 had strong correlation with DAS28 (r=0.87/r=0.93),SDAI (r=0.92/r=0.99),p<0.001. Bland-Altman plot showed better agreement between DAPSA/DAPSA28 for low than high disease activity (figure).

Construct validity: DAPSA/DAPSA28 were similarly correlated to HAQ; r=0.60/0.62, p<0.001. DAPSA/DAPSA28 discriminated patients reporting their symptom state acceptable (n=1140) vs. not acceptable (n=1045) equally well: mean(SD) 9.1(8.7)/8.4(8.0) and 24.2(14.9)/22.5(13.8), respectively.

Conclusion: DAPSA28 showed good criterion, correlational and construct validity. Agreement between DAPSA and DAPSA28 was better for low than high disease activity levels. The original DAPSA should be preferred in PsA. However, data sets with only 28 joint counts available can be used to calculate DAPSA28.

Disclosure: B. Michelsen, None; J. Sexton, None; J. S. Smolen, None; D. Aletaha, None; N. S. Krogh, None; D. van der Heijde, None; T. Kvien, AbbVie, Biogen, BMS, Boehringer Ingelheim, Celgene, Celltrion, Eli Lilly, Epirus, Hospira, Merck-Serono, MSD, Mundipharma, Novartis, Oktal, Orion Pharma, Hospira/Pfizer, Roche, Sandoz and UCB, 5, 8,AbbVie, BMS, MSD, Pfizer, Roche, UCB., 2; M. L. Hetland, AbbVie, Biogen, BMS, Celltrion, MSD, Novartis, orion, Pfizer, Samsung, USB, 2, 5, 8,AbbVie A/S, Biogen (Denmark) A/S, Bristol-Myers Squibb Danmark, Eli Lilly Denmark, MSD Danmark ApS, Novartis Danmark A/S, Pfizer Danmark ApS, Roche A/S, UCB Nordic A/S., 2.

To cite this abstract in AMA style:

Michelsen B, Sexton J, Smolen JS, Aletaha D, Krogh NS, van der Heijde D, Kvien T, Hetland ML. Can Disease Activity in Patients with Psoriatic Arthritis be Adequately Assessed By a Modified Disease Activity Index for Psoriatic Arthritis (DAPSA) Based on 28 Joints? [abstract]. Arthritis Rheumatol. 2018; 70 (suppl 9). https://acrabstracts.org/abstract/can-disease-activity-in-patients-with-psoriatic-arthritis-be-adequately-assessed-by-a-modified-disease-activity-index-for-psoriatic-arthritis-dapsa-based-on-28-joints/. Accessed .

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