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- PATIENTS AND METHODS
Rheumatoid arthritis (RA) is a chronic inflammatory disease that ultimately leads to joint destruction and permanent disability. However, early in the disease course, the inflammatory process leads to a multitude of functional limitations (1–5). Several studies have also shown that RA is associated with a shortened life span, mainly due to coronary vascular disease (6–8). Wolfe et al recently reported that patients' self-assessed functional impairments, using the Health Assessment Questionnaire (HAQ), are the best predictors of life expectancy compared with laboratory, radiographic, and physical examination data (9). Early use of potent antirheumatic therapy is advocated to improve the outcome (10).
Typically, disability in RA diminishes within the first year after diagnosis and start of intervention, and then either remains stable but still affected (11) or slowly worsens over time (2, 12). Two recent Swedish studies on early RA have found that women on average have more pronounced difficulties in performing daily activities than men as reflected by the HAQ (13, 14). Apart from sex, factors such as age, disease activity, and joint destruction have been found to correlate with HAQ score (4, 15–18). Also, by using another instrument designed to evaluate activity limitations in patients with RA, the Evaluation of Daily Activities Questionnaire (EDAQ), women have been found to be more disabled than men (5, 19). Similar to healthy individuals, women with RA have a substantially lower average grip force than men with RA (5, 20–23). Several studies have also found that grip force is associated with disability (5, 20, 24–26).
In a review of sex-based differences in patients with RA, Harrison pointed out the need for studies that highlight sex differences to optimize intervention strategies in women and men (27). The purpose of the present study was to investigate possible differences between women and men concerning grip force and activity limitation 3 years after the diagnosis of recent-onset RA, and to determine if activity limitation correlates with grip force.
- Top of page
- PATIENTS AND METHODS
In the present study, we investigated the relationship between grip force and difficulty performing activities assessed by the HAQ and EDAQ. The HAQ was used on a routine basis at all followups. The EDAQ was used at 3 visits to identify difficulties in performing daily activities with the intention to facilitate planning and to evaluate the effects of assisstive devices (5). On average, the HAQ as well as the EDAQ, which both include many activities that are dependent on the upper extremities, revealed more pronounced difficulties for women. Using regression analysis, we found that grip force was the strongest regressor when HAQ and EDAQ were analyzed together. Also, when we regressed HAQ separately, grip force was the strongest regressor, closely followed by walking speed, SOFI lower extremity, and pain. The same regressors were significant when EDAQ was regressed separately, although here walking speed was strongest, closely followed by grip force. Sex and age were not identified as significant regressors of HAQ and EDAQ. The degree of activity limitation, as measured by the HAQ and the EDAQ, was associated with grip force. Therefore, we found that both women and men with low average grip force (<114 N) had substantial activity limitations, indicating a need for multiprofessional intervention. Conversely, women and men with a grip force corresponding to that of healthy women (>214 N) (33) had very low HAQ scores. Our results regarding the relationship between activity limitation and grip force corroborate the results of a recently published study where increased values in performance-based functional measures (grip strength, timed button test, and walking velocity) displayed a proportional increase in self-reported disability (34).
The finding of lower grip force values in women with RA, as compared with men with RA, is not surprising because this is also the case in healthy individuals. Women and men with RA had approximately the same relative degree of grip force reduction, resulting in grip force values of men comparable with those of healthy women in most cases. Because many of the functional abilities assessed by the HAQ and EDAQ require strong hands, it is not surprising that women with RA on average proved to be more affected than men by means of these instruments. However, when women and men with RA were subgrouped together with regard to grip force, it became evident that poor outcome assessed by the HAQ and EDAQ was related to low grip force, but not to sex (or age) per se. The activity limitations seen 3 years after the diagnosis of RA were of approximately the same magnitude as those seen after 1 and 2 years in both women and men (5). Several investigators, using the HAQ, have reported more pronounced activity limitations in women than men (2, 4, 13–15, 18, 35), and this finding, together with a majority of other self-reported outcome measures, has been considered an indication of a more severe disease course in women (16). The HAQ score has also been found to increase with increasing age in patients with RA as well as in healthy individuals (35), and Kuiper et al have argued that the postmenopausal state may be responsible for the difference in outcome between women and men (17). As judged by our results, however, grip force under or above a critical level, rather than sex, age, or postmenopausal state, may be the most important explanation to activity limitation. Therefore, women and men with comparable grip force values also had comparable outcome measures by means of the HAQ and EDAQ. Interestingly, however, when women and men were subgrouped according to grip force, the men appeared to be more severely affected with regard to measures of systemic inflammation.
In line with our findings, Krishnan et al recently reported that there were no significant differences in the HAQ score between women and men in a general population in Finland with a mean age of 55 years (33). However, besides differences in grip force, HAQ score, and EDAQ score in our cohort, there was a small but significant difference in SOFI upper limb, where men had higher scores indicating more functional impairment. This small difference is also seen in a Swedish reference population, which is age and sex matched to the TIRA cohort (unpublished observations), indicating that this difference is dependent on sex.
Grip force and walking speed from inclusion through 1-year followup in the Swedish TIRA cohort were also found to be significant regressors of self-reported variables (36). Compared with a healthy Swedish reference population (21), the grip force reduction in patients with RA with a disease duration of 12 years was ∼75% in women. Men, having approximately double the average grip force of women, end up with a normal female grip force after a 50% reduction. Therefore, the 50% grip force reduction in patients with RA, as seen in both women and men in this study, could be expected to have less impact on the HAQ and EDAQ outcomes in men. The common observation that women have a more severe form of RA than men could possibly, at least in part, be misleading due to the female-biased design of the HAQ and EDAQ, which to a great extent evaluate traditional female activities. However, Wolfe et al reported that HAQ score is an even better predictor of life expectancy in men than in women (9). After subdividing RA patients into 4 groups with respect to absolute values of grip force, the sex differences concerning HAQ and EDAQ outcomes disappeared. This, however, does not exclude that grip force/hand function and other functional abilities may also be associated with disease activity (12). Our findings highlight the fact that the HAQ score in a study group is dependent on the percentage distribution of women and men, respectively. This needs to be taken into consideration when comparing HAQ scores between study groups with different distributions of female and male patients.
Several studies have reported that grip force increases as a result of interventions (30, 37–42). The results in the present study also indicate that increasing the grip force may result in reduced activity limitations. However, further studies are needed to evaluate interventions directed to reduce disabilities and to analyze the relationships between different aspects of disability.
In conclusion, activity limitations are closely related to grip force, followed by walking speed and SOFI lower extremity, regardless of sex. By grouping patients with respect to grip force, we found that men and women with similar grip force had equal degrees of self-reported activity limitation. This finding offers an explanation as to why women report more pronounced activity limitation than men. Therefore, low grip force is closely related to activity limitation regardless of sex. At the same time, we found that subgroups of patients with low or no activity limitation had an average grip force corresponding to the average grip force of healthy women. In clinical practice, grip force measurement is simple and rapidly performed, and the absolute grip force can be used as an indicator to identify patients with activity limitations and a need for multiprofessional intervention.