Defining minimal disease activity in psoriatic arthritis: a proposed objective target for treatment

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Abstract
Objective: To create minimal disease activity (MDA) criteria for psoriatic arthritis (PsA). With recent therapeutic advances, this is now a goal for treatment and may represent a measure to compare therapies. It defines a satisfactory state of disease activity rather than a change, and encompasses all aspects of the disease. Methods: 40 patient profiles were sampled from an observational PsA database. Sixty experts in PsA classified these as in MDA or not. A consensus of ⩾70% was accepted, identifying 13 profiles in MDA. Summary statistics created possible cut-off points for the definition. Considering the number of measures that must be met, 35 candidate definitions were created and tested using receiver operating characteristic curves (ROC) for sensitivity and specificity. Results: Four candidate definitions showed high area under the curve values on ROC testing. Definitions with high outlying values were excluded as they were not considered to represent MDA. Aiming for high specificity to reduce false positives resulted in a preference for the following definition: “A patient is classified as achieving MDA when meeting 5 of the 7 following criteria: tender joint count ⩽1; swollen joint count ⩽1; Psoriasis Activity and Severity Index ⩽1 or body surface area ⩽3; patient pain visual analogue score (VAS) ⩽15; patient global disease activity VAS ⩽20; health assessment questionnaire ⩽0.5; tender entheseal points ⩽1”. Conclusion: This study provides the first definition of a “state” of MDA in PsA and defines a target for treatment. It must now be validated in other populations and tested in clinical trials.