Measurement of disease activity in psoriatic arthritis. Extended report.

OBJECTIVE: To determine whether activity indices, generally accepted in rheumatoid arthritis (RA) are useful and valid to measure disease activity in psoriatic arthritis (PsA) patients with peripheral arthritis.

METHODS: 38 PsA patients were studied before and after a one year DMARD treatment. Extended and reduced tender and swollen joint counts, Ritchie articular index, Health Assessment Questionnaire HAQ) score, erythrocyte sedimentation rate (ESR) morning stiffness, the patient's and the assessor's global assessment (PGA and AGA) were recorded. Disease activity scores, EULAR, ACR and Clegg improvement criteria were calculated.

RESULTS: All indices correlated well before and after treatment with AGA (r > 0.337, p < 0.042), except morning stiffness and tender joint counts. After treatment, PGA correlated well only with the 68 and 28 tender joint counts, ESR and HAQ (r > 0.340, p < 0.05). The response to DMARD treatment was well characterized with the changes in the number of tender and swollen joint counts, and DAS4, DAS3, DAS28. The changes correlated with the PGA and AGA. The level of agreement between Clegg and the EULAR improvement criteria with both extended and reduced joint count was comparable (p < 0.01).

CONCLUSION: The well-known activity indices generally accepted in RA, as tender and swollen joint count, DAS3, DAS4, DAS28, are useful and valid indices measuring arthritis activity in PsA with peripheral arthritis. The correlation between Clegg and EULAR improvement classification indices were similar. Both seemed to characterize changes authenticated during DMARD treatment.