A proposal on how to assess the weight of the subjective components of the DAPSA in patients with psoriatic arthritis and comorbid fibromyalgia syndrome

OBJECTIVES: To establish the weight of the subjective components of the Disease Activity index for Psoriatic Arthritis (DAPSA) in psoriatic arthritis (PsA) patients and comorbid fibromyalgia syndrome (FM). METHODS: In PsA patients not fulfilling the DAPSA remission, it has been calculated the DAPSA-patient (DAPSA-P), an index represented by the ratio between the sum of the subjective components (tender joint count+patient global assessment of disease activity+visual analogue scale pain) and DAPSA in its entirety (swollen joint count+tender joint count+patient global assessment of disease activity+visual analogue scale pain+C-reactive protein [in mg/ dl]). The DAPSA-P ranges from 0 to 1, and values closer to 1 suggest a major weight of the subjective components, while values closer to 0 indicate a greater contribution of the swollen joint count and C-reactive protein, the two factors more closely related to inflammation. It was also defined as the presence of a comorbid FM, and it was established the DAPSA-P cut-off point distinguishing for the presence of a comorbid FM through the receiver operating characteristic (ROC) curve analysis. RESULTS: DAPSA-P was higher in all PsA+FM patients. Analysing the receiver operating characteristic curve, the DAPSA-P cut-off distinguishing a comorbid FM was 0.775. CONCLUSIONS: DAPSA-P can help to measure how comorbid FM inflates DAPSA.