Psoriasis has a substantial impact on patients' lives. Measures of disease status alone are generally considered insufficient to describe the burden of illness (Wilson and Cleary, 1995;Muldoon et al, 1998) and the physician assessment of the extent of apparent disease in psoriasis has been shown to be frequently a questionable indicator of disease severity and impact (Marks et al, 1989;Finlay, 1997;Fortune et al, 1997a,2002). More patient-centered measures seem to be necessary to consider the patient's appraisal of the disease as it affects physically, psychologically, and socially his or her quality of life (McKenna and Stern, 1996;Kirby et al, 2001). Until now, several instruments have been created to evaluate the quality of life of patients with psoriasis (Finlay and Coles, 1995;Gupta and Gupta, 1995;McKenna and Stern, 1997) or in general with dermatologic diseases (Finlay and Khan, 1994;Chren et al, 1997). These instruments, which consist of self-administered questionnaires given to the patients, try to reflect the way in which patients perceive and react to their health status, assessing objective functioning, subjective well-being, or both (Muldoon et al, 1998). Although they do not include any direct information on clinical severity, it is interesting to explore whether these measures are in some way correlated to measures of disease status.
In this study, we quantified the clinical severity of psoriasis using both physician- and patient-centered indexes, and we measured the health-related quality of life, using disease-specific as well as specialty-specific instruments. In addition, we assessed psychiatric morbidity with a validated questionnaire. We aimed at describing the degree of correlation between these measures, and we performed a cluster analysis to investigate how they group together.
In this article we report results from data collected in a large sample of patients of psoriasis hospitalized at the Dermatological Institute IDI-IRCCS of Rome, included in our ongoing IDI Multipurpose Psoriasis Research on Vital Experiences (IMPROVE) study.
Results
In the survey days, there were 1237 hospitalizations for psoriasis at IDI, regarding 1025 patients. Of these, 137 did not satisfy the inclusion criteria. Of the 888 eligible individuals, 102 did not agree to enter the study, so the participation rate was 88.5% (n=786).
The mean age of the patients was 45.5 y, and there were 465 men (59.2%) and 321 women. The majority of patients had generalized plaque psoriasis (47.1%), 16.8% localized plaque, 12.8% guttate, 7.9% arthropatic, 7.3% palmoplantar, and 2.0% pustular psoriasis. Erythrodermic psoriasis and other rare forms (i.e., generalized, inverse, follicular, and nail psoriasis) were grouped together because of the small number of cases. The mean PASI score was 8.6 and the mean age at onset was 33.6 years. As for global severity as assessed by dermatologists, 24.7% of patients were classified as severe or very severe, 29.0% as moderate, and 46.3% as mild.
Figure 1 shows the tree diagram for all the clinical severity, quality-of-life, and psychological distress instruments. The diagram was built on the basis of the similarity between the instruments, measured by the correlation coefficients shown in Table I. On the first steps, the emotions and social functioning subscales of Skindex, DLQI, PDI, IPSO, and PLSI merged in a group with high correlation values, from 0.815 (Skindex emotions and Skindex social functioning) to 0.600 (Skindex emotions and PDI). The GHQ was then added to the previous group, with correlation coefficients between GHQ and the grouped instruments from 0.484 (PLSI) to 0.666 (IPSO). On the following step, the symptoms subscale of Skindex merged in the previous group (correlation coefficient from 0.433 to 0.598 with the other instruments). PASI and SAPASI merged in a separate group. The correlation coefficients between them and all the other instruments ranged from 0.049 for the correlation between GHQ and PASI to 0.359 for the correlation between PLSI and SAPASI. Therefore, at the end of the clustering process, two main clusters could be identified, one including only PASI and SAPASI and the other encompassing all the quality of life and psychological distress instruments. The replication of the cluster analysis on five different random subsamples of the study population gave the same results, thus supporting the validity of the clusters obtained in the main analysis.
Figure 1.
Tree diagram resulting from hierarchical cluster analysis of measures of clinical severity, quality-of-life, and psychological distress instruments.
Full figure and legend (6K)Table I - Correlation matrix of clinical severity, quality-of-life, and psychological distress instruments.
Full table When considering the different levels of some sociodemographic and clinical variables, a poor correlation was invariably observed between clinical severity and quality-of-life measurements. The majority of the correlation values ranged from 0.1 to 0.3 for both psoriasis-specific and dermatology-specific indexes. In general, the correlations between quality-of-life measures and SAPASI were slightly higher than those with PASI. Correlations between all quality-of-life instruments and PASI and SAPASI were slightly higher in women than in men (e.g., r=0.171 and r=0.277 in men and women, respectively, for the correlation between PASI and PDI) and slightly increased with increasing severity. As to clinical type, in psoriatic arthritis and in the guttate form correlations were higher than in the other clinical types (e.g., respectively, r=0.247 and r=0.257 between PASI and PDI).
As to psychological distress indexes, PASI and SAPASI were more correlated with PLSI than with GHQ in all levels of the considered variables. Moreover, the trend of the correlation between clinical severity instruments and PLSI was similar to the one observed with quality-of-life instruments, whereas no particular trends were observed in the correlations with GHQ.
No significant differences were observed in the other sociodemographic variables, such as education and marital status. Also in variables related to clinical characteristics and symptoms, correlations between quality-of-life indexes and clinical severity measurements were poor and did not show significant differences in the different levels of the variables.
Time of completion was <24 h from admission in approximately 55% to 60% of patients for the different questionnaires and 
48 h only in 12% to 15% of cases. No time-of-completion-related differences were observed. For example, the correlation coefficients between PASI and SAPASI in the four time categories of SAPASI completion were 0.633, 0.650, 0.630, and 0.653. Correlation coefficients between PASI and the first quality of life completed instrument (Skindex, social functioning) were 0.222, 0.166, 0.283, and 0.194, whereas between PASI and the last completed quality-of-life instrument (PLSI) they were 0.328, 0.174, 0.301, and 0.234.
Discussion
In our study, cluster analysis showed two distinct groups of instruments, one including only PASI and SAPASI, and the other encompassing all quality of life and psychological distress indexes. In addition, clinical severity measurements showed almost invariably, for the different levels of the various factors of interest, a poor correlation with different indexes of quality of life and psychological distress in patients with psoriasis. These results were strikingly similar when considering the clinical severity evaluation performed either by the physician (PASI) or by the patient (SAPASI).
A possible limitation of our observations is that they were derived from patients hospitalized for psoriasis. Although it is probable that our study population is selectively enriched with more severe cases, it should be considered that psoriasis hospitalization patterns in Italy are vastly different from the United States and other countries. In fact, as it can be seen from the description of the population under Results, a large proportion of cases with mild to moderate severity, as well as a wide range of clinical types, are included in our study.
Previous studies investigating the relationship between clinical variables and quality of life in psoriasis have also found poor correlation (Fortune et al, 1997a,2002;Touw et al, 2001), with coefficients comparable to our results (i.e., in the range of approximately 0.15–0.40). Such poor correlations do not seem to depend, in our study, on the time interval between PASI assessment and questionnaire completion. In fact, SAPASI was given as the last instrument and its correlation with PASI was excellent. In addition, among the quality-of-life instruments, PLSI was the last to be completed, but it showed the highest correlation with PASI, whereas GHQ was completed as second but gave the only non-statistically significant correlation with PASI. Furthermore, the stratified analysis (see Results) showed that correlation coefficients did not change with increasing time intervals between PASI and quality-of-life assessment.
In contrast, the high correlation between quality-of-life instruments does not seem to be due to test fatigue nor to a possible "halo effect." For instance, we have checked correlations between similar items in different questionnaires (e.g., item 4 of Skindex-29, "My skin condition makes it hard to work or do hobbies," and item 7 of DLQI, "Has your skin prevented you from working or studying?"), and we observed that correlation coefficients were similar in the different combinations of time-of-completion categories.
Measures of health-related quality of life should consider patients' objective functioning or subjective well-being or both (Muldoon et al, 1998). It is clear that whereas functional assessment is expected to be close in some way to clinical status, subjective well-being concerns the way in which patients live with their disease and it does not necessarily depend completely on severity. As has been pointed out (Guyatt et al, 1993), quality of life is at least partly independent of health status and "is a reflection of the way that patients perceive and react to their health status and to other nonmedical aspects of their lives" (Gill and Feinstein, 1994). This would be particularly true if, as has been suggested (Gill and Feinstein, 1994;Anonymous, 1995), only perceived well-being, not functional assessment, were used to determine quality of life. The instruments we used in our study included both objective functioning and subjective well-being components, even though in different proportions. In instruments intended to assess the psychosocial impact of psoriasis, such as PLSI and IPSO, the subjective component is predominant. Nevertheless, the personal evaluation of problems in daily activities, which is scrutinized through several questions in PDI and DLQI, also has a strong subjective component in addition to a connection with clinical severity of the disease. On its side, GHQ considers only the subjective well-being, because it is intended to assess psychological distress. The predominance of the subjective component in our quality-of-life instruments could explain the poor correlation between them and clinical severity measurements. As a matter of fact, the personal way of coping with psoriasis, like many other dermatologic diseases, is not necessarily correlated to the extent of the disease or to clinical characteristics such as desquamation, induration, or erythema, considered as main features of the disease by PASI and SAPASI. Moreover, it has been demonstrated that subjective indices of quality of life correlate reliably with standard measures of psychiatric symptoms such as depression or anxiety, suggesting in this sense that they do measure subjective well-being, thus satisfying the criterion of convergent validity (McHorney et al, 1993). It is of some relevance to note that the correlation between the symptoms scale of Skindex-29 and both PASI and SAPASI is strikingly poor (r=0.122 and r=0.175, respectively). Although this scale is close to the concept of clinical severity, it includes symptoms such as itching, bleeding, and burning, which are actually not taken into account in disease severity measurements, such as PASI and SAPASI.
Moreover, the similarity of the results concerning PASI and SAPASI is not surprising, because these measures have been shown to be highly correlated (Sampogna et al, 2003). As a matter of fact, even though compiled by the patient, the SAPASI score is based on observable signs of disease and does not consider symptoms nor implications on patients' emotional life and social functioning. It is interesting to note how the SAPASI appears to constrain patients to provide an objective assessment of their lesions, relatively unpolluted by their subjective impression of the impact of those lesions on their lives.
Psoriasis-specific quality-of-life instruments do not correlate with PASI and SAPASI better than the dermatology-specific ones, such as DLQI and Skindex. Indeed, disease-specific instruments strongly correlate with dermatology-specific ones, with the exception of the symptoms scale of the Skindex-29, thus suggesting that they collect very similar information on quality of life. This observation shades some doubts, as recently noted though for different reasons (de Korte et al, 2002), on the opportunity to use psoriasis-specific quality-of-life instruments given that they do not allow to make comparisons with other skin conditions.
The dissimilarity between clinical severity assessment and patient-centered measures stresses the need for reconceptualization of psoriasis severity. It has been recently proposed (Krueger et al, 2000) that a quality-of-life standard would be better than a body surface area measurement for delineating psoriasis severity. Our results indicate that both approaches may be necessary for discriminative purposes (i.e., to measure differences cross-sectionally between patients in different groups) and for evaluative purposes (i.e., to measure differences longitudinally to study, for example, the natural history of the disease or to evaluate a new drug for approval). In fact, changes in clinical severity reflect the biologic relevance of an intervention (e.g., a new treatment), whereas quality of life measures quantify how those changes impact on the daily life of the patients.
In the years of the third revolution in medical care (McKenna and Stern, 1996), with the necessity of focusing on the person rather than the disease, a more comprehensive assessment of psoriasis seems to be necessary. The road for future studies, intended to blend diverse measures into a comprehensive one with solid quantitative features and good psychometric properties, seems to be well delineated.
Materials and Methods
Participants
This study was carried out on patients with psoriasis enrolled in a wider project on clinical, epidemiologic, emotional, and quality-of-life aspects of psoriasis (IMPROVE study). Data included in this report were collected between February 21, 2000, and July 31, 2001, at the inpatient wards of the Istituto Dermopatico dell'Immacolata (IDI-IRCCS), a large dermatologic hospital located in the city of Rome, Italy. Presently, at IDI-IRCCS a wide range of clinical presentations of psoriasis are hospitalized, including at times mild and moderate severity cases. Such patients come especially from the more disadvantaged central and southern regions for diagnostic procedures and treatments (e.g., PUVA) that may not be available in their areas of residence.
During the study period, patients hospitalized at IDI-IRCCS with a diagnosis of psoriasis were contacted by our research staff. After the diagnosis of psoriasis was confirmed by the senior staff of the hospital, specifically trained dermatologists verified the inclusion criteria and explained the purposes and methods of the study to the patients. Inclusion criteria were 18 y of age or more, absence of any severe mental or physical illness, at least 5 y of education, ability to read Italian, and first hospitalization for psoriasis since the date of the beginning of the study. All eligible patients who gave their written informed consent were recruited in the study. Ethical approval was granted by the Institutional Review Board and the study was carried out in compliance with the Declaration of Helsinki guidelines.
Instruments
Clinical severity instruments
Psoriasis Area and Severity IndexClinical severity was assessed by the physicians using the psoriasis area and severity index (PASI) (Fredriksson and Pettersson, 1978;Marks et al, 1989;Ashcroft et al, 1998). To complete the PASI, the dermatologists had to estimate the proportion of involved area for each body district (head, trunk, upper and lower extremities). The area of psoriatic involvement for each of the four regions was then assigned a numerical value of 0 to 6 corresponding to 0% to 100% involvement: 0, no involvement; 1, < 10%; 2, 10% to < 30%; 3, 30% to < 50%; 4, 50% to < 70%; 5, 70% to < 90%; and 6, 90% to 100%. For each region, erythema, desquamation, and induration of the plaques were rated according to the classical 5-point scale: 0, no involvement; 1, slight; 2, moderate; 3, marked; and 4, very marked.
PASI scores were then calculated by investigators using electronic spreadsheets to implement the formulas originally proposed (Fredriksson and Pettersson, 1978). The PASI score can vary from 0 to 72, with higher scores indicating more severe conditions.
Self-administered PASIPatients determined clinical severity completing the self-administered PASI (SAPASI) (Feldman et al, 1996). It is a structured, validated instrument, which we previously tested in subgroups of this study population, showing excellent acceptability (Sampogna et al, 2003). It consists of a line-drawing silhouette of the front and back of a body for patients to shade in the affected areas and of three visual analog scales for recording the erythema, induration, and scaliness of one's own average lesion. Based on the silhouette shading, a physician who had not seen the patients and was blind to PASI scores assigned a numeric value of 0 to 6 to the area of psoriatic involvement using the same cut points of PASI (see above). SAPASI scores were calculated as originally proposed (Feldman et al, 1996). The range and interpretation of SAPASI scores are the same as those of PASI.
Health-related quality-of-life instruments: psoriasis-specific
Psoriasis Disability IndexThe Psoriasis Disability Index (PDI) (Finlay and Kelly, 1987;Finlay and Coles, 1995) is a validated self-administered questionnaire which consists of 15 questions covering aspects of functional disability owing to psoriasis. To answer the questions, patients had to refer to the immediately preceding 4 wk. The 15 questions were grouped under four headings: daily activities, work, personal relationship, and treatment. Answers were recorded on a 4-point linear scale, indicating grades from "not at all" to "very much." The total score was obtained by summing the scores given to each question.
Impact of psoriasis on quality of lifeThe Impact of Psoriasis Questionnaire (IPSO) (McKenna and Stern, 1997) assesses the impact of psoriasis on patients' physical, psychological, and social functions. It is a self-administered questionnaire, with 16 questions based on those used in the Medical Outcomes Study Short-Form General Health Survey (Stewart et al, 1989). We considered the sum of the scores for each question (from 0 to 4) as the total score.
Health-related quality-of life instruments: dermatology-specific
Skindex-29Skindex-29 is a reliable and valid instrument that has been specifically designed for measuring health-related quality of life in dermatologic patients (Chren et al, 1997). It is constituted by three scales assessing areas considered essential in any instrument purported to assess quality of life: burden of symptoms, social functioning, and emotional state. The Italian version of this self-administered questionnaire has been recently validated (Abeni et al, 2001,2002). Patients answered the 29 questions referring to the previous 4-wk period, on a 5-point scale, from "never" to "all the time." The total score of each scale was given by the sum of the scores given to each question.
Dermatology Life Quality IndexThe Dermatology Life Quality Index (DLQI) is a 10-item self-administered questionnaire (Finlay and Khan, 1994) designed to provide a simple method of measuring the disability experienced by patients with skin diseases. The patients answered the questions considering the previous week on a 4-point scale, indicating "not at all,""a little,""a lot," and "very much," respectively. The total DLQI score represents the sum of the scores for each question.
Specific and generic measures of psychological distress
Psoriasis Life Stress InventoryThe 15-item version of Psoriasis Life Stress Inventory (PLSI) (Gupta and Gupta, 1995) was developed to measure stress associated with potential psoriasis-related psychosocial problems. Subsequent research (Fortune et al, 1997b) has shown that the PLSI addresses specifically: (1) stress resulting from anticipatory/avoidance coping behavior that is effected to limit the sociocognitive intrusiveness of psoriasis and (2) stress resulting from patients' actual experiences or beliefs of being evaluated by others solely on the basis of their skin. For each item, the patient was asked to rate the level of stress experienced over the previous month on a 4-point scale, from "not at all" to "a great deal." The PLSI score was calculated by summing the scores for each question.
General Health QuestionnaireThe 12-item General Health Questionnaire (GHQ) is a self-administered questionnaire designed to measure psychological distress and to detect current nonpsychotic psychiatric disorders (Goldberg, 1972). Questions refer to the most recent weeks. The 12-item Italian version was used (Bellantuono et al, 1987). The reliability and validity of this instrument has been consistently demonstrated, recently also in dermatologic patients (Picardi et al, 2001). Scores are given on a 4-point linear scale and higher scores on the GHQ-12 indicate a higher level of psychological distress.
Assessment procedures
During the first hours of hospitalization, before any medication was administered, the dermatologists assessed the clinical severity using the PASI. They also collected information on sociodemographic variables, clinical history, and other factors of clinical interest (e.g., clinical type and location of the disease, personal and family history of psoriasis and other diseases, symptoms). At the end of the visit, the physician rated the global severity of the disease on a 5-point scale used in previous studies (Chren et al, 1997;Abeni et al, 2002). The two higher classes of severity were grouped together because of scarce numbers.
After the visit, the self-administered questionnaires, each stapled separately, were given to the patients in the following order: sociodemographic information and history, Skindex-29, GHQ-12, PDI, DLQI, IPSO, PLSI, and SAPASI. Patients were instructed to complete the questionnaires as soon as possible, but at the same time without feeling overburdened; they also had to record time and date of completion on each questionnaire. Before hospital discharge, the patients returned all the self-administered questionnaires to their physicians.
Statistical analysis
A single linkage hierarchical cluster analysis (Sokal and Michener, 1958) was performed on the different instruments to see whether groups with similar characteristics could be identified. We used Pearson correlation coefficient (r) as a measure of similarity between variables. The sequence of mergers of clusters was visually represented by a tree diagram. As a validation of the results obtained, we performed a replication procedure: the same analysis was conducted on different random samples, each including 50% of the total study population.
We then analyzed more in detail the correlations between the clinical severity measured by PASI and SAPASI and the quality of life as assessed by all the other instruments, considering them in different levels of many variables. The considered variables were sex, age, marital status, education, age at onset, duration and severity of psoriasis, clinical type, localization, and symptoms. All analyses were performed using the logarithm of PASI and SAPASI scores, because of skewness in the distributions of the values of both measures, to comply with a basic assumption of the analysis of correlation (i.e., normal frequency distribution of the measures to correlate). The other scores were not transformed, because we observed that logarithmic or square root transformation, although slightly improving the symmetry of distributions, did not change the results.
To verify whether correlation coefficients could be influenced by the time interval between the completion of the questionnaires we performed a stratified analysis after classifying the questionnaires into four categories based on time of completion: < 24, 24 to 35, 36 to 47, and 48 h from admission. All statistical analyses were performed under SPSS, version 9.0 for Windows (Norusis, 1999).
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Acknowledgments
This study was partially supported by Grant ICS-120.4/RF98.7 of the "Progetto Ricerca Finalizzata," and by "Progetto Ricerca Corrente–Dermatoepidemiologia—2001–2002" of the Italian Ministry of Health, Rome, Italy. The IDI Multipurpose Psoriasis Research on Vital Experiences (IMPROVE) investigators who contributed to this study are Massimo Alotto, Gianluca Antonelli, Simone Bolli, Rino Cavalieri, Massimo Luca Chinni, Marcello Fazio, Giampiero Girolomoni, Elisabetta Luchetti, Eva Mazzotti, Carmelo Franco Melchi, Nidia Melo Salcedo, Paola Moscatelli, Paolo Pasquini, Paolo Piazza, Angelo Picardi, Orietta Picconi, Maria Antonietta Pilla, Grazia Primavera, Pietro Puddu, Paolo Ruatti, Giuseppe Ruggiero, Valentina Salvatori, Romeo Simoni, Donatella Sordi, and Albertina Tiago.
