A cross-sectional, observational, multi-centre study was conducted involving 18 centres in Spain. Information on patient clinical characteristics and HRQL was collected by a dermatologist and rheumatologist working together in each centre. The study was approved by the Clinical Research Ethics Committee for all of the participating centres, and informed consent was signed by all of the subjects in the study. The recruitment period was from January to March 2007.

The patient inclusion criteria were the following: (1) age >18 years; (2) a diagnosis of psoriatic arthritis confirmed by a dermatologist and rheumatologist; and (3) capacity to understand the questionnaires used in the study. The exclusion criteria were the following: (1) current participation in a clinical trial; (2) receiving biological therapy apart from infliximab; and (3) axial disease involvement.

The demographic data collected in the study included age, gender, illness duration, weight, date of the psoriatic arthritis diagnosis and loss of productivity.

Three different measures were used to describe the severity of psoriatic arthritis: (1) Psoriasis Area and Severity Index (PASI); (2) Health Assessment Questionnaire (HAQ); and (3) number of swollen and tender joints.

The PASI score considers the severity of psoriasis as a function of the area of skin involved and the grade of erythaema, desquamation and/or infiltration.15 The final score has a range from 0 to 72, which is the weighted sum of different area scores. The affected surface is measured in 4 different areas, head, trunk, upper extremities and lower extremities, each scored between 0 and 6. The erythaema, desquamation and infiltration scores range between 0 and 4.

The HAQ assesses impairment in daily activities due to illness.16 The items contained in the HAQ are a sample of 20 daily activities divided into 8 different dimensions (dressing and grooming, awakening, eating, walking, hygiene, reach, grip and other activities). The patient can choose between 4 different responses (no difficulty, some difficulty, considerable difficulty and incapable). Apart from these questions, the patients are asked some questions regarding the need for physical aids or assistance from another person to perform these activities. Each HAQ dimension score ranges from 0 (without impairment) to 3 (unable to do), and the summary score is the mean of the 8 HAQ dimensions.

A printed picture of the human body was used by the researchers to help the patient to identify and record the number of swollen and tender joints.

Two questionnaires were used to define the HRQL: (1) EuroQol-5D (EQ-5D), and (2) Short-Form 36 (SF-36). The EQ-5D is composed of 5 items, each one assessing different dimensions of quality-of-life in a range of 1 to 3.6,17,18 A score of 3 for an item represents the worst level of function. The final score is descriptive and is represented by five numbers, for example, 11213, with each number representing the score for each item. Utility values can be computed based on these scores.19 The utility value represents the patient's health state between 0 (death) and 1 (best possible health state). Furthermore, a Visual Analogue Scale (VAS) was included in the questionnaire. The patients used this scale to self-assess global HRQL. The scale is represented by a printed thermometer with a scale ranging from 0 (poorest quality-of-life) to 100 (best possible state of quality-of-life).

In the SF-36, the patients graded 36 items representing 8 different HRQL domains.5,8,9,20,21 The scores were transformed onto a 0 to 100 scale, with higher scores representing the best self-assessment for the domain. Two summary factors were computed using this questionnaire: physical component summary (PCS) and mental component summary (MCS). These components were generated by a factor analysis that has been validated in Spain.8,22

Statistical analyses were performed using PASW® 18.0 (Predictive Analytics Software) software. Descriptive statistics and statistical tests were performed. Categorical variables were assessed using the chi squared test or Fisher exact test, and quantitative variables were analysed using a Student t test or ANOVA. The level of significance was set to 0.05.

To estimate the influence of demographic and clinical variables on the impairment of daily activities (measured by HAQ) and HRQL (measured by EQ-5D and SF-36), multivariate analysis (multivariate linear regressions) was performed. The specified dependent variables were summary HAQ score, EQ-5D utility values, and the PCS and MCS from the SF-36 questionnaire.

The study included 287 patients with psoriatic arthritis, with 71 (24.7%) patients receiving infliximab. The patient demographics are shown in Table 1. The mean (±SD) age was 52.4 (±12.5) years, and the mean weight was 76.5 (±15.1)kg. Additionally, 56% of the patients were male. Of the 287 patients, 16 (6%) lived alone. No significant differences were found in the demographic characteristics between the patients receiving or not receiving infliximab.

No significant differences were found between the patients receiving or not receiving infliximab for clinical variables, except for the number of swollen joints. The patients receiving infliximab had a lower mean number of swollen joints than patients not receiving infliximab (1.54 vs. 2.98) (Table 1). The mean (±SD) years of disease duration was 10.9 (±9.6). The mean number of tender joints was 5.0 (±6.9), with a maximum number of 49 tender joints.

The mean (±SD) PASI score was 3.7 (±5.8), with a minimum score of 0 and a maximum score of 51. The mean PASI cut-off score for moderate severity psoriatic symptoms was <10. The majority of patients (91.3%) had a PASI score below 10, 6.6% of patients had a PASI score of 10–20 and only 2.1% of patients had a PASI score greater than 20.

Thirty percent of patients reported that, on some days during the previous month, they were unable to perform standard daily activities. The mean number (±SD) of days per month that patients were unable to do their daily activities was 12.8 (±10.7), and the hours per day that patients felt unable to do their daily activities was 9.0 (±7.1). Additionally, 21% of patients felt the need to request help from friends/family to perform the most common daily life activities.

Of the 287 patients, 55% were employed at the time of the study, and 16% retired early due to the psoriatic arthritis (Table 2). Six percent of patients had changed their job because of the illness. The mean (±SD) reduction in working hours per week was 0.8 (±3.3), and the mean (±SD) income reduction per month was 7.6 (±52.9) euros/patient. No significant differences were found with regard to productivity loss between the patients receiving or not receiving infliximab.

Significant differences were found in almost all of the HAQ dimensions between the patients receiving and not receiving biological therapy. However, patients receiving infliximab had higher impairment in daily activities than patients managed without infliximab (overall mean HAQ 0.93 vs. 0.70, p=0.011). The detailed results are shown in Table 3.

The multivariate analysis showed that the main factors that affected the performance of the daily activities measured by the HAQ were receiving infliximab, sex, age and the number of swollen and tender joints. From these variables, the major influence was due to the sex and receiving biological therapy. Men receiving infliximab had greater impairment in daily activities.

Regression analyses with HRQL as a dependent variable showed that patients with a higher number of tender joints had a worse HRQL. Pain was the most influential variable on HRQL measured using the EQ-5D and SF-36. Other variables with some influence in HRQL were sex and age. Older patients and women have a higher risk of HRQL impairment. Detailed results of multivariate analyses are shown in Table 6.

The authors declare that the procedures followed were in accordance with the regulations of the responsible Clinical Research Ethics Committee and in accordance with those of the World Medical Association and the Helsinki Declaration.

The authors declare that they have followed the protocols of their work centre on the publication of patient data and that all the patients included in the study have received sufficient information and have given their informed consent in writing to participate in that study.

The authors have obtained the informed consent of the patients and/or subjects mentioned in the article. The author for correspondence is in possession of this document.