Measure for measure. Outcome assessment of arthritis treatment in clinical practice

University dissertation from Clinical Sciences, Lund University

Abstract: Objective: To investigate (i) the performance and agreement between various activity indices and response criteria in TNF-blockade of RA; (ii) the predictive ability of different response criteria and disease activity states regarding continuation of anti-TNF treatment of RA; (iii) Euro-QoL-5-dimensions utility development during TNF blockade of RA, PsA and SpA. Also, (iv) to develop a simple, utility-based outcome measure, the number needed to treat per quality adjusted life year gained (NNQ) and apply it in RA, PsA and SpA patients on anti-TNF treatment.
Methods: Data were retrieved from the South Swedish Arthritis Treatment (SSATG) register. In patients with RA, PsA and SpA commencing treatment with adalimumab, etanercept or infliximab, date of treatment start and stop, core set variables and EQ-5D were recorded, and various activity indices, responses and EQ-5D utility were calculated. Descriptive statistics and completer analysis were used. The NNQ was calculated as the inverted value of the area under the utility gain curve for one year.
Results: Agreement between RA response criteria was poor at the individual level, except at the ACR20/overall level. Disease states exhibited moderate or good agreement at all levels and for most criteria sets, except for remission. Response at ACR20/overall and ACR50/good/major level was found to significantly predict treatment continuation, for most indices already after 6 weeks. EQ-5D utilities improved rapidly (at 2 weeks in RA and PsA) and remained stable over 5 years in TNF blockade of RA, PsA and SpA. NNQ for TNF blockade of RA, PsA and SpA and was found to be 4-6, irrespective of diagnosis and treatment course order.
Conclusions: Response criteria are less suitable for use in individual patients in routine care than disease activity states in RA. By contrast, they are often useful as predictors of continued TNF blockade. EQ-5D utility rises almost instantaneously in TNF blockade and remains stable in RA, PsA and SpA patients remaining on therapy. NNQ is easy to calculate and understand and performs well across 3 diagnostic entities.