Results

One hundred and forty five patients were eligible for the study. Twelve patients were excluded because they moved away at the start (n = 7), had a language problem (n = 3) or refused to participate (n = 2). One hundred and thirty three patients were included in the study of which 111 (83 %) completed the one year follow up (table 1).

The reasons for loss to follow up were death (n= 3: malignancy (n= 2) and renal failure (n= 1)), non-compliance (n=13) and moving home (n= 6). Eight of 13 patients dropping out because of non-compliance were not willing to comply with the protocol although they kept coming to the rheumatologist. The baseline disease characteristics of the 22 patients lost to follow up were similar to those of the 111 completers (data not shown) except for the percentage of IgM-RF positive patients, which was significantly lower in the group of drop outs (45% versus 54%: p = 0.05). The mean ESR in the group of the non-completers at time of drop out (after a mean of three months) was 30 mm 1st h versus 26 in the group of the completers.

PREDICTORS OF FUNCTIONAL STATUS AT ONE YEAR

During the one year follow up 85% of the patients were treated with one or more DMARDS: hydroxychloroquine (13%), sulfasalazine (47%), methotrexate (22%) and auranofin (2%). Furthermore, 77% had received physical therapy and 21% occupational therapy.

The median HAQ score at one year was 0.53 (range 0–2.3). The course of the HAQ and DAS scores over the first year is shown in figure 1. The correlation between the HAQ score at one year and the various predictor variables as measured at entry was less strong than at entry (table 2, right column). The HAQ score at entry had the strongest relation to the HAQ score at one year. The results of the logistic regression analysis of functional status at one year are shown in table 3. Only the variables HAQ and pain at entry contributed significantly to the predictive model of parameters that correlated with HAQ at one year. Patients with a high HAQ score at entry were 2.9 times more likely to belong to the group “more disabled” after one year than those with a low HAQ score. The functional status could be predicted with an accuracy of 73% according to the entry HAQ and pain score.

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Figure 1

Change of mean HAQ and DAS scores between entry and one year: comparison of the less disabled versus more disabled group partitioned by HAQ 50th percentile at one year.

Discussion

In this group of RA patients with disease duration shorter than three years, the most reliable predictors of functional status at entry are the disease activity parameters DAS score and CRP concentration, whereas the most reliable parameters that predict the functional status after one year are the HAQ and the pain score. The duration of complaints was not related to the functional status at entry or after one year.

The observation that the duration of complaints is not associated with the HAQ score might be because of selective referral. Mild cases may not be immediately referred by the general practitioners, whereas patients with an aggressive onset are presumably sent to the hospital quickly. This is in accordance with Wolfe18 who concluded that patients who are admitted to the hospital in an early stage of their illness usually have more severe disease than those who visit the outpatient clinic later. Furthermore, a selection was made by including only patients with less than three years of complaints in this study. Consequently, the variability in duration of complaints is limited, which may explain the negative result of the possible relation between the HAQ and the duration of complaints. In contrast, Harrisonet al 19 showed that a longer duration of symptoms was related to a decrease in functional capacity. However, their population consisted of patients with RA and undifferentiated inflammatory polyarthritis.

Most of the studies on predictive factors of functional capacity used either the HAQ or Steinbrocker's functional grades as outcome parameter.5 ,11 ,19-21 The HAQ is widely used and consequently this index is included in the ACR 1991 functional status criteria for RA.22 According to Thompsonet al 20 the HAQ performs well and, as a measure of the patients' perspective of disease reflects the true needs of patient care. Although the HAQ is the most frequently reported parameter of function, there are limitations for its use as well.23 According to van den Ende24 sex and disease duration confound the HAQ scores. In this study though, no significant baseline differences in these variables were found between the more or less disabled groups at one year.

In this study, functional outcome could be predicted at one year correctly in 73% of the patients using relatively simple entry measures as pain, HAQ and DAS score. No relation was found between sociodemographic factors and entry HAQ score. This is in contrast with the findings of Vliet Vlieland25 who concluded that a low level of education was correlated to a high number of erosions and a high HAQ score at entry.

Van der Heide et al 26 similarly concluded that disability at one year could be predicted correctly for 79% of the patients by entry HAQ and pain. The majority of studies of early arthritis confirm that initial functional status is the most important predictor of functional capacity at one year or more with an accuracy between 67% and 80%.4 ,5 ,11 ,19 ,26 As the HAQ at entry is the most powerful predictor of the HAQ after one year, other variables that are highly correlated with the HAQ will lose predictive power in the stepwise logistic regression analysis and therefore may not be included in the model. In this study, this is illustrated by the DAS at entry, which shows a strong correlation with the HAQ at one year in the univariate analysis. Therefore, the DAS remains an important predictor of future functional status next to the HAQ.

Several authors confirm the association between CRP, DAS score and HAQ score, but found other significant variables as well.5 ,11 ,19 ,27 ,28 Other factors associated with a high HAQ score are: female sex, a longer disease duration and large joint involvement (at one year)19; patient's global assessment of disease activity, morning stiffness and grip strength (at two years)5 and a positive IgM-RF (at six years).11 After a 12 year follow up age, female sex and radiological progression4 show a correlation with the HAQ.

There seems to be a difference in nature of predictors of functional status between short-term and long term studies. This could explain why in contrast with Sherrer4 and van Zeben,11this study and another26 with shorter term of follow up, the radiological progression and IgM-RF were not found to be predictors of the HAQ score. The disease severity of our patients according to the percentage of patients with a positive rheumatoid factor and erosive disease did not differ much from other studies. The early RA patients of this study are comparable with another study on early RA in the Netherlands according to the number of IgM-rheumatoid factor positive patients.10

In conclusion, the most reliable predictors of functional status at one year were the HAQ score and the level of pain in this group of patients with early RA. Many disease activity parameters correlated significantly with the functional status at entry, whereas disease duration and sociodemographic characteristics did not. Referral seems to be prompted by severity rather than by duration of arthritis. This study demonstrates that the HAQ is highly correlated with the DAS during the first year. Therefore, a goal of treatment is to decrease the DAS as soon as possible to maintain functional capacity.