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).
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.
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.
DAPSA-P can help to measure how comorbid FM inflates DAPSA.