Functional disability in rheumatoid arthritis patients compared with a community population in Finland

Authors


Abstract

Objective

To compare Health Assessment Questionnaire (HAQ) scores of patients with rheumatoid arthritis (RA) with HAQ scores from a sex- and age-adjusted population.

Methods

Patients with RA (n = 1,095) and control subjects (n = 1,530) completed a mailed questionnaire that comprised the HAQ, pain and global health scores, education level, and comorbidities, as well as height, weight, and lifestyle attitudes, including smoking and exercise habits.

Results

The HAQ scores increased (indicating declining function) with older age in patients and controls. The HAQ scores were above the reference values (>95th percentile of the HAQ scores of the age- and sex-matched population) in 17–45% of women with RA and in 7–32% of men with RA ages 30–79 years, while the HAQ scores of the patients ≥80 years were similar to those of the age- and sex-matched population. In a logistic regression model, the odds ratio for disability (HAQ score ≥1; at least some difficulties in most activities of daily living) was 7.7 (95% confidence interval 5.3–11.1; P < 0.001) among patients with RA compared with community controls, when adjusted for age, sex, education, smoking, exercise, body mass index, number of comorbidities, and pain.

Conclusion

RA is associated with a >7-fold risk of disability compared with that in a general population of adults in the same community. The impact of disability due to RA appears to be greater in younger and middle-age people than in elderly patients.

The Health Assessment Questionnaire (HAQ) was developed two decades ago to measure functional outcomes of patients with arthritis. This questionnaire is a valid self-report measure, and scores are sensitive to change in patient functional status over time (1, 2). It has been translated into many languages and is used extensively in rheumatology clinics worldwide. The HAQ is part of the core data set used to assess outcomes of patients with rheumatoid arthritis (RA) in clinical trials and in longitudinal observational studies (3, 4).

Disability according to the HAQ has been studied in large population-based studies, including a cohort of men and women >50 years old (5), a cohort of long-distance runners >50 years old (6), and a cohort of elderly subjects who were university alumni (7). However, disability measured by the HAQ has not been reported in the general population in all adult age groups. Furthermore, disability rates according to the HAQ in patients with RA have not been compared with those of the general population. Therefore, we conducted a cross-sectional survey to compare the HAQ scores of patients with RA, who were identified in the Central Finland RA database, with the HAQ scores of control subjects living in the same district and matched with the patients by age and sex. Furthermore, we also examined the impact of pain and global health scores, number of comorbidities, body mass index (BMI), education level, and personal lifestyle choices, such as smoking and exercise habits, on the self-reported HAQ disability.

PATIENTS AND METHODS

Location.

The Central Finland district is located in the Southern part of Finland. Its population of 263,869 (in 2000) is 5% of the total population of Finland.

Patients with RA.

Jyväskylä Central Hospital is the only rheumatology center in the Central Finland district. All new patients with RA are referred to this center for diagnostic studies and initiation of therapies. Most patients with severe RA visit the outpatient or inpatient clinic regularly. The Central Finland RA database includes demographic measures, treatments, and outcomes of all patients with RA seen in the clinic since January 1993. It is updated daily by a research nurse. By June 2000, the database contained 1,763 RA patients, 1,495 of whom were still living. These 1,495 patients were mailed a questionnaire. The questionnaire results were entered into the RA database and analyzed along with the patient's disease characteristics and treatments.

Controls.

To obtain a population sample, the names and addresses of 2,000 people who were at least 30 years old and living in the district were requested from the Ministry of Social Affairs and Health. The sample was drawn from a database that includes an identification number, date of birth, demographic data, name, and address of all individuals living in Finland. In order to match the RA patient group by age and sex, the population sample was designed to have a mean age of 55 years and to include 70% women, but was otherwise random. The sampling was performed by Statistics of Finland. This organization administratively operates under the Ministry of Finance, but is fully and independently responsible for its statistics. Statistics of Finland obtains the majority of the data from diverse administrative registers, and produces two-thirds of all government statistics in Finland (see their web site at www.stat.fi).

Study design.

A questionnaire was mailed to 1,495 patients with RA and to 2,000 controls in June 2000. A reminder was sent 8 weeks later to nonresponder controls.

Functional status in activities of daily living was measured by the Finnish version of the HAQ (8), including 20 questions in 8 categories: dressing, rising, eating, walking, grooming, reaching, gripping, and performing errands. The response alternatives available were 0 = no difficulty, 1 = some difficulty, 2 = much difficulty, and 3 = unable to do. The sum of the highest response in each category was divided by 8 to form a score range of 0–3. Pain and global health status were assessed on a 100-mm visual analog scale.

The presence of comorbidities was also queried. In addition to RA, the conditions reported included hypertension, coronary artery disease, other heart disease, asthma, chronic bronchitis, chronic kidney disease, peptic ulcer, inflammatory bowel disease, diabetes, thyroid disease, cancer, epilepsy, stroke, Parkinson's disease, psoriasis, chronic leg ulcers, ankylosing spondylitis, osteoarthritis, fibromyalgia, chronic back pain, musculoskeletal trauma, mental illness, and alcoholism. The number of comorbidities was calculated as a plain sum of these conditions.

Sex, date of birth, and height were recorded along with weight to calculate the BMI (the weight in kilograms divided by the square of the height in meters). Other variables queried were the years of education, current and previous smoking habits (never/ever), and frequency of physical exercise (for example, walking, skiing, bicycling, swimming, jogging, or exercising in a gym) with response alternatives “3 or more times weekly,” “1–2 times weekly,” “sometimes (<1 time weekly),” or “not at all.”

Statistical analysis.

Reference values for the HAQ scores were set at ≤95th percentile of the HAQ scores of the normal population (9), in the age groups 30–39, 40–49, 50–59, 60–69, 70–79, and ≥80 years in women and men. The percentages of RA patients who had HAQ scores >95th percentile were calculated and assessed separately according to age and sex.

A HAQ score ≥1 indicates that there is at least some difficulty in most activities of daily living. Therefore, the HAQ cutoff value of ≥1 is a clinically relevant definition for “disability” in general. We examined associations of disability (HAQ score ≥1) with RA in a logistic regression model (10), with age, sex, education, smoking, exercise, BMI, number of comorbidities, and pain as covariates.

The probability distribution of the HAQ scores in patients and in controls was illustrated by a violin plot (11). Analyses were performed with SPSS (Chicago, IL) and STATA (College Station, TX) software. The study was approved by the ethics committee of Jyväskylä Central Hospital.

RESULTS

Characteristics of patient population. A total of 1,095 patients with RA (73% of 1,495) returned a completed questionnaire. The mean age of the respondents was 62.4 years (range 19–96), 71% were female, the mean disease duration was 11.3 years (median 8.7 years), 68.6% (of 1,013 patients who were tested) were positive for rheumatoid factor, and 60% had erosions on their hand or foot radiographs. The median delay from the first symptoms to the initiation of treatments with disease-modifying antirheumatic drugs (DMARDs) was 6 months. A total of 82% of the patients were currently taking DMARDs, including 48% taking methotrexate, 30% taking sulfasalazine, 13% taking hydroxychloroquine, and 12% taking intramuscular gold, either as a single DMARD (66% of those who took DMARDs) or in combinations (34% of those who took DMARDs). In addition, 35% of the patients were taking prednisone (median 5 mg a day).

Characteristics of control population. A total of 1,533 control subjects (77% of 2,000) returned a completed questionnaire. The mean age of the respondents was 55.4 years (range 30–91 years), and 72% were female.

Comparison of disability. The HAQ scores increased with older age in patients and controls. The HAQ scores of patients with RA who were ages 30–79 years were above the reference values (>95th percentile of the scores for the age- and sex-matched population) in 17–45% of women and in 7–32% of men, while the HAQ scores of the patients ≥80 years were similar to those of the age- and sex-matched population (Table 1). The violin plot demonstrates differences in the probability distribution of the HAQ scores in patients and in controls (Figure 1). Accordingly, the percentage of patients with disability (HAQ score ≥1) was greater among patients with RA when compared with the controls (Figures 2A and B for women and men, respectively). In a logistic regression model, the odds ratio for disability was 7.7 among patients with RA (95% confidence interval 5.3–11.1, P < 0.001) compared with the control population, when adjusted for age, sex, education, smoking, exercise, BMI, number of comorbidities, and pain (Table 2).

Table 1. Percentage of patients with RA who reported HAQ scores greater than the reference values*
Age group, yearsFemaleMale
HAQ reference valuesRA patients with HAQ scores >95th percentile, %HAQ reference valuesRA patients with HAQ scores >95th percentile, %
  • *

    Reference values for the Health Assessment Questionnaire (HAQ) scores were defined as ≤95th percentile of the scores among the control population. RA = rheumatoid arthritis.

30–390.47536.60.81322.2
40–490.53144.71.01320.7
50–591.25017.10.75032.0
60–691.23826.20.87527.7
70–792.15617.12.4507.1
≥803.0000.02.7500.0
Figure 1.

Violin plot of the distribution of the Health Assessment Questionnaire (HAQ) scores in patients with rheumatoid arthritis (RA) and the general population controls. The plot shows the median (indicated by the small, open horizontal band), the first through the third interquartile range (the thick, solid vertical band), and estimator of the density (thin vertical curves) of the HAQ score in each group (comparable to a box plot, except that the distribution of the variable is illustrated as density curves).

Figure 2.

Distribution of RA patients (▪) and controls (░;) with disability according to a HAQ score ≥1, by age group (in years) and by female (A) or male (B) sex. See Figure 1 for definitions.

Table 2. Odds ratios for being disabled according to the HAQ (HAQ score ≥1) by a logistic regression analysis*
 Odds ratio95.0% confidence intervalP
LowerUpper
  • *

    BMI = body mass index (see Table 1 for other definitions).

Patients with RA vs. controls7.6785.30511.113<0.001
Increasing age in years1.0231.0071.0390.004
Females vs. males1.6151.1242.3200.010
Decreasing education in years1.0220.9691.0770.425
Smokers vs. nonsmokers1.1430.6861.9050.607
Exercise none vs. other categories3.0681.9764.764<0.001
BMI ≥30 vs. BMI <30 kg/m20.8560.5841.2570.428
Increasing no. of comorbidities1.1481.0371.2720.008
Increasing pain1.0531.0461.061<0.001

DISCUSSION

For the first time, normative data on HAQ disability in the general adult population, including all age groups, are presented. The reference values were set at the 95th percentile of the HAQ scores, adjusted by age and sex. Knowing reference values allows for HAQ disability scores to be compared across age, sex, and disease. For example, if a 35-year-old man or an 85-year-old woman with RA had a HAQ score of 1, would that mean that the level of the disability was the same for both? In fact, both experienced at least some difficulties in most activities of daily living, but without reference values from the background population, it was not possible to determine whether the level of the disability in these example cases was different from that of people of the same age and sex in general. Therefore, the reference values of the HAQ that are presented herein may contribute to better understanding of HAQ scores of patient groups and individual patients with RA.

In 30–79-year-old patients with RA, 17–45% of women and 7–32% of men reported HAQ scores greater than the adjusted reference values. This observation is expected, since functional disability in activities of daily living became a well-known characteristic of RA in the 1980s (12, 13). Introduction of patient self-report func- tional status questionnaires (1, 14, 15) made it easy to measure the functional status of the patients in rheumatology clinics. However, until now, the HAQ scores of the general adult population including all age groups have not been formally reported, nor have HAQ scores of patients with RA been compared with those of the general population.

This study reveals an unexpected observation that the HAQ scores of older patients with RA were similar to the HAQ scores of the age- and sex-adjusted population. Therefore, the impact of disability due to RA appears to be greater in younger and middle-age people than in elderly patients. The limitation of our study is that it was conducted in one district only, where the population is homogenous. The results may be extrapolated to other populations that are similar to that of the Central Finland district, e.g., other Scandinavian countries. However, reference values of the HAQ should be evaluated in populations other than Scandinavian populations to confirm our results.

The study included patients with RA who were seen in Jyväskylä Central Hospital since 1993. These patients had been treated with DMARDs according to the “sawtooth” strategy (16). This means that DMARD therapy was instituted soon after the diagnosis, and available DMARDs were used serially and continuously as single drugs or in combinations. In spite of active treatments with traditional DMARDs, the proportion of RA patients with disability was substantially higher compared with the age- and sex-adjusted population. Treatments with new medications such as tumor necrosis factor inhibitors will hopefully lead to better functional outcomes in patients with RA.

Acknowledgements

The authors thank Mr. Tuukka Tarkiainen and Ms Sari Leinonen for excellent data management, Ms Leena Miina and R. N. Marjo Kortemaki for work with the Central Finland RA database, research analysts Christopher Swearingen and Melissa Gibson for English revision of the manuscript, and Drs. Theodore Pincus, James Fries, and Helen Hubert for helpful advice concerning the manuscript.

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