The utility of patient-based disease activity score for routine practice in rheumatoid arthritis

Abstract

Rheumatoid arthritis (RA) patients have joint pain, swelling, deformities and disability as a result of inflammation. New Disease Modifying Anti-Rheumatic Drugs (DMARD) including biologics have made “treat-to-target” a realistic standard practice aiming at sustained remission to prevent joint damage. Remission is defined by disease activity measurements conducted by doctors and blood tests. However, this limits the frequency of disease activity assessment. Patient-based Disease Activity Score (PDAS) was developed in the UK to allow patients to report their symptoms and come up with a score that closely resembles the doctors’ assessment. The second formula of PDAS (PDAS2) can do it even without the need for a blood test.

This thesis explores how PDAS agrees with the doctors’ assessment, sees if PDAS2 can be further simplified, if it works as well in Chinese patients, and if home PDAS2 monitoring can give some useful predictions on the worsening of RA (flare) and the need to step up DMARD.

First, the agreement between PDAS2 and the doctors’ scales of RA activities was moderate to substantial, similar to that between two standard doctors’ scales. Few patients under-reported their symptoms and even fewer over-reported them.

Second, PDAS2 contains four components to make up a score: patient’s overall impression of RA activity, functional disability, self-rated joint swelling and stiffness in the morning. All of them were measuring different aspects of RA activity, and the total score changed as RA activity changed, particularly for flares. Although some components were heavier weighted than the others, none should be discounted.

Third, the Chinese translation of PDAS2 was shown to be valid and work equally well among Hong Kong Chinese patients to inform RA activity and flare.

Lastly, from a major hospital in Hong Kong, 92 RA patients completed home monitoring using Chinese PDAS2 questionnaire. On average, they did it every two weeks for 16 weeks between two clinic visits. PDAS2 scores of each recording were computed, and then a time-integrated cumulative PDAS2 score (cPDAS2) was calculated to take into account of the variable time intervals between each recording. This score described the overall trends of RA activity at home and could predict doctors’ assessment at the next clinic visit. The cPDAS2 score could predict patients in sustained remission or low activity if the score remained low and without significant fluctuations. Patients who had flare would have cPDAS2 score increased to a high level or by a significant amount. More importantly, the cPDAS2 score also predicted the doctors’ intention to intensify DMARD treatment. Therefore, home PDAS2 monitoring can reassure stable RA patients, and also help to identify patients who are having a flare or worsening disease, for earlier clinic review on treatment to meet the goal of “treat-to-target”.

In summary, this thesis has shown that RA patients can use PDAS2 to monitor their own disease activity as routine care. The Chinese version of PDAS2 performed similarly to the original version. Home monitoring of disease activity using cPDAS2 may improve implementation of “treat-to-target” by identifying worsening disease prior to scheduled clinic visits.