Background/Purpose: Psoriatic arthritis (PsA) dactylitis is associated with an increased risk of erosions and higher disease activity. Dactylitis treatment strategies are however controversial due to the absence of evidence from randomized controlled trials studying dactylitis as a primary outcome. The objective of this trial was to assess the efficacy of golimumab in combination with methotrexate (MTX) versus MTX monotherapy in active PsA dactylitis.

Methods: GO-DACT was a proof-of-concept multicentric, investigator-initiated randomized, double-blind, placebo-controlled, parallel-design, phase 3b trial. PsA patients, fulfilling the ClASsification for Psoriatic ARthritis criteria, naïve to MTX and biologic disease modifying anti-rheumatic drugs (bDMARDs), with active dactylitis, were randomly allocated to receive subcutaneous injections of golimumab 50mg or placebo, administrated every four weeks for 24 weeks, both in combination with MTX. The primary endpoint was the change from baseline in the Dactylitis Severity Score (DSS) assessed at week 24. Key dactylitis secondary endpoints included DSS20, 50 and 70 response rates, changes and response rates in the Leeds Dactylitis Index (LDI20, 50 and 70) and changes in the magnetic resonance imaging (MRI) dactylitis score. Analysis was by intention to treat for the primary endpoint.

Results: 44 patients were centrally randomized, 21 to golimumab plus MTX and 23 to placebo plus MTX, for 24 weeks, and 1 patient from each arm dropped out. The median baseline DSS was 6 in each arm. The mean MTX dose reached in the golimumab plus MTX group was 16.3mg/week and in the MTX monotherapy group was 19.2mg/week. Patients treated with golimumab plus MTX experienced significantly greater improvements in the DSS at week 24 (median change of 5) as compared to the MTX group (median change of 2) (p=0.026). At week 24, significantly higher proportions of patients treated with golimumab plus MTX achieved DSS50/70 responses, as well as LDI20/50/70 responses (p< 0.05). At week 24, significantly lower median dactylitis MRI scores were observed in patients treated with golimumab plus MTX in comparison with those treated with MTX monotherapy (p=0.017). The median changes from baseline in the Disease Activity Score 28 (DAS28), the Disease Activity Index for PsA (DAPSA), the PsA Disease Activity Score (PASDAS) and the target Nail Psoriasis Severity Index (tNAPSI) at week 24, were significantly higher for those treated with golimumab plus MTX. Patient’ inclusion was halted at 50% of recruitment due to a favorable interim analysis. There were no new safety issues for golimumab during this trial.

Conclusion: GO-DACT shows additional benefits from the combination of golimumab and MTX as first-line bDMARD therapy versus MTX monotherapy, in the treatment algorithm of active PsA dactylitis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/go-dact-a-phase-3b-randomized-double-blind-placebo-controled-proof-of-concept-trial-of-golimumab-plus-methotrexate-mtx-versus-mtx-monotherapy-in-improving-dactylitis-in-mtx-naive-psoriatic-arthr/