SEARCH

SEARCH BY CITATION

Keywords:

  • Epidemiology;
  • joint damage;
  • psoriasis;
  • psoriatic arthritis

Abstract

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

Abstract

Background  Psoriatic arthritis (PsA) is a chronic, systemic, inflammatory disorder characterized by the association of arthritis with psoriasis. Patients with PsA may have a heterogeneous and variable clinical course. Evidence that affected patients can have significant radiographic joint damage, functional impairment, reduced quality of life and long-term work disability is increasing.

Objectives  This study aims to determine the prevalence and clinical features of psoriatic arthritis and joint complaints in patients with psoriasis examined in a German national survey.

Methods  This study is a non-interventional, cross-sectional analysis on 2009 patients with psoriasis from 13 dermatological hospitals and 129 dermatological private practices and outpatient clinics in Germany. Patients showing rheumatological symptoms were further recorded with respect to active arthritis and PsA symptoms according to Group for Research and Assessment of Psoriasis and Psoriatic Arthritis criteria.

Results  Nineteen per cent of the patients had PsA, including 14.8% previously confirmed and 4.2% newly diagnosed disease. Another 7.7% had intermittent but clinically unspecific joint symptoms, which could not be clearly attributed to PsA. About half (49.7%) of the patients with PsA had at least 1 swollen joint and 84.9% (n = 287) suffered from joint pain. Patients suffering from pain marked an average of 8.7 joints on a diagram as painful out of a possible 28. The mean number of swollen joints among the affected patients amounted to an average of 6.8.

Conclusion  Our results show that there is still a significant number of patients suspected of having joint involvement without ever having been diagnosed with PsA. Recently published data indicate that progression of joint damage and functional disability can be prevented if adequate treatment is started promptly. Early diagnosis and interdisciplinary care are thus crucial.


Introduction

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

For a long time, the prevalence and clinical spectrum of inflammatory arthritis in patients with psoriasis were unknown.1 The proportion of psoriasis patients suffering from psoriatic arthritis (PsA) was earlier reported as approximately 5–10%.2–4 More recent investigations showed a proportion of over 20%.5 A 2005 epidemiological study carried out in Italy on 936 psoriasis patients found the proportion of PsA to be 7.7%.5 This study underlined the difficulty in reliably differentiating joint involvement of psoriasis from joint complaints of other origin. In a US survey of patients identified from a random sample of the population, it was revealed that the prevalence of PsA among patients with psoriasis is 11%.6 However, PsA is statistically more prevalent among patients with more severe psoriasis. Regardless of the exact prevalence rate, PsA is of great socioeconomic importance because of its frequency and considerable disease burden.7

The clinical picture of PsA is highly variable and covers a heterogeneous group of inflammatory changes to joints (arthritis), bones, and juxta-articular tendons and ligaments (dactylitis, enthesitis), that can be associated with the symptoms of an inflammatory reaction (pain, joint effusions, reddening and swelling over a joint).8 Asymptomatic disease already exhibiting objective changes to joints or juxta-articular structures is not rare. The heterogeneous nature of the disease and its frequently unpredictable course, have, over the last decades, inevitably led to a large number of different classifications.9–14 The most frequently used classification of PsA that is still used today is that of Moll und Wright.15 This classification comprises five subtypes: asymmetric oligo-arthritis (about 70% of cases), symmetric polyarthritis (20%), distal interphalangeal arthritis (5–10%), mutilating arthritis (5%) and arthritis of the spine (5–40%).

A frequent characteristic of PsA is the heterogeneity of the forms and the often unpredictable dynamics of the potentially progressive and destructive course of the disease. Clinical characteristics particularly typical of PsA are the axial involvement of joints, a dactylitis (16–49% of cases) in which the basal, middle and end joint of a toe or finger is affected,16 as well as osteodestructive and proliferative changes to the joint. The following are the risk factors for a severe course of the disease: an early age at first manifestation, female sex, polyarticular involvement, genetic predispositions17 and radiological signs of PsA at an early stage. The methods for diagnosing PsA have already been significantly refined by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA).18

In order to ensure suitable care, especially of severely affected patients with psoriasis and PsA, it is important to know the prevalence of these courses of the disease and, thus, optimize access to new drugs. For this reason, the first nationwide study on the prevalence of PsA in Germany, which was carried out on the basis on a diagnosis algorithm, was undertaken in private dermatological practices and hospitals.

Objective

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

The aim of the present study was to record the prevalence and clinical characteristics of PsA and joint complaints among patients with confirmed psoriasis in Germany on the basis of a nationwide sample.

Methods

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

Study design

We carried out a nationwide, multicentre observational study (National Health Services Study on Psoriasis vulgaris 2007 – PsoHealth) on psoriasis patients in dermatological hospitals and community-based private dermatological practices. The design and conduct of the study were undertaken by the Competence Centre for Health Services Research in Dermatology at Hamburg-Eppendorf University Hospital (CVderm). The study was carried out in accordance with the GEP criteria and the Declaration of Helsinki, under notification of the competent Ethics Committee of the Hamburg Chamber of Physicians. Patients (> 18 years) with any form of psoriasis who were willing to participate were included in the study.

Data collection

The data collection was aimed at the competitive inclusion of 2000 patients. Patients were enrolled in the centres consecutively by the participating dermatologists after informed consent had been obtained. The questionnaires for doctors were completed in the respective cooperation centre by the attending physician. The patient questionnaires were filled in by the patients themselves and then returned to the doctor. Monitoring involved CVderm telephoning the dermatological practices initially once a week and later once a month and the field force visiting the practices every 2 weeks.

The following target parameters were recorded:

  • 1
    Patient history, sociodemographic data, previous and current treatment
  • 2
    Severity of psoriasis using the Psoriasis Area and Severity Index (PASI), the Dermatology Life Quality Index (DLQI), and the EuroQol
  • 3
    Description of the quality of care, the ‘Care index’, from quality indicators
  • 4
    Patient benefits and subjectively experienced quality of care (Patient Benefit Index and Care Index – Patient)
  • 5
    Diagnosis and clinical symptoms of PsA

Psoriatic arthritis

The diagnosis of PsA was made on the basis of a multilevel diagnosis algorithm. First, it was determined whether the PsA had already been confirmed in a previous diagnosis (Fig. 1). If this was the case, this was documented and the status of the joints recorded.

image

Figure 1. Psoriatic arthritis decision tree model.

Download figure to PowerPoint

If joint symptoms and a previously unconfirmed PsA were present, the dermatologist answered a list of questions about the clinical symptoms relevant to the PsA (Fig. 1). This list of questions, which were based on the GRAPPA criteria18 and the published outcomes criteria,19,20 was drawn up by an expert consensus between dermatologists and rheumatologists. The presence of a PsA was then assessed by the doctor and the planned diagnostic measures were stated. The status of the patient's joint was recorded with ‘clinically probable’ or ‘previously confirmed PsA’.

Data evaluation

After the double entry of all data by trained data managers, the two sets of data were compared and all divergent entries corrected on the basis of the original forms. All data were analysed with descriptive statistics and specified in terms of statistical standard values (absolute and percentage frequencies for categorical data; mean, standard deviation for continuous data). A sample size analysis was carried out for the calculation of the statistical power. Statistical differences between groups were calculated using a two-sided Fisher test. The evaluation was carried out using SPSS 12.0 for Windows.

Results

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

A total of 2038 questionnaires filled by physicians and 2040 filled by patients were returned to the study centre. Data sets from 2009 patients (56.3% men, 43.7% women) complied with the inclusion and exclusion criteria (Fig. 2). The average age of the patients was 51.5 ± 14.6 years (Table 1). On average, psoriasis had first been diagnosed 21.3 years ago. Of the patients, 86.6% suffered from chronic plaque psoriasis, 23.3% from guttate psoriasis, 4.6% from flexural psoriasis and 1.5% from pustular psoriasis. Nail involvement was present in 35.6% of cases. The mean PASI score was 10.1. There were no significant differences in the above-mentioned outcomes between dermatological clinics and office-based dermatologists (data not shown). Thirty-three per cent of the patients (n = 657) had a PASI of < 5; 28.0% (n = 557), 5–10; 27.4% (n = 545), 10–20; and 11.6% (n = 231), > 20. Among the affected patients, 40.5% had a positive family history (Table 2). Of the 58.1% working people; 4.3% were unfit to work at the time of questioning, with about half having been incapacitated for 11 days or more (median = 11 days). 14.5% of those working had been unfit for work because of the psoriasis at least once in the past year.

image

Figure 2. Flow chart of the patient recruitment.

Download figure to PowerPoint

Table 1.  Sociodemographic and general data
 Psoriatic arthritis probable or confirmedPsoriatic arthritis uncertain or ruled outP (two-sided)Total
Applicable nApplicable % (95% CI)NApplicable nApplicable % (95% CI)NFisher testApplicable nApplicable % (95% CI)N
  1. *NA, statistical conditions for the calculation of a confidence interval not met.

Sex female17045.337568543.315830.4985643.71960
 (40.3–50.4)  (40.8–45.7)   (41.5–45.9) 
Underweight51.3375352.215790.42402.01956
(Men: BMI < 20, Women: BMI < 19) (NA*)  (1.5–2.9)   (1.4–2.7) 
Normal weight7620.337551932.91579< 0.001*59530.41956
(Men: BMI 20–25, Women: BMI 19–24) (16.2–24.3)  (30.6–35.2)   (28.4–32.5) 
Overweight19150.937572545.915790.0891746.91956
(Men: BMI 26–30, Women: BMI 25–30) (45.9–56.0)  (43.5–48.4)   (44.7–49.1) 
Obese9926.437527117.21579< 0.001*37119.01956
(BMI 31–40) (21.9–30.9)  (15.3–19.0)   (17.2–20.7) 
Markedly obese41.1375291.815790.38331.71956
(BMI > 40) NA  (1.2–2.5)   (1.1–2.3) 
 RangeM ± SD (95% CI)NRangeM ± SD (95% CI)Nt-testRangeM ± SD (95% CI)N
Age21–8653.6 ± 12.4 (52.3–54.8)37118–9351.0 ± 15.0 (50.3–51.8)15710.001*18–9351.5 ± 14.6 (50.9–52.2)1944
BMI (Women)18.7–47.127.8 ± 4.9 (27.0–28.5)17016.2–58.326.3 ± 5.3 (25.9–26.7)6810.001*16.2–58.326.6 ± 5.2 (26.3–27.0)852
BMI (Men)18.5–53.227.9 ± 4.4 (27.2–28.5)20415.0–58.027.0 ± 4.3 (26.6–27.2)8890.005*15.0–58.027.1 ± 4.3 (26.8–27.3)1094
Table 2.  Patient statements about history of psoriasis (n = 2009)
 Psoriatic arthritis probable or confirmedPsoriatic arthritis uncertain or ruled outP (two-sided)Total
Applicable nApplicable % (95% CI)NApplicable nApplicable % (95% CI)NFisher testApplicable nApplicable % (95% CI)N
First-grade relative with PSO16243.537263839.816030.2080140.51977
 (38.5–48.6)  (37.4–42.2)   (38.4–42.7) 
Working19050.337896360.116030.001*115358.11983
 (45.2–55.3)  (57.7–62.5)   (56.0–60.3) 
Only if working: currently unfit for work 105.5183353.79350.30454.01118
 (2.2–8.8)  (2.5–5.0)   (2.9–5.2) 
Only if working: at least 1 day unfit due to PSO in the past 12 months 4425.117511312.5907< 0.001*15714.51082
 (18.7–31.6)  (10.3–14.6)   (12.4–16.6) 
Hospitalized for at least 1 day due to PSO in the past year13336.536424916.21533< 0.001*38220.11899
 (31.6–41.5)  (14.1–18.1)   (18.3–21.9) 
 RangeM ± SD (95% CI)NRangeM ± SD (95% CI)Nt-testRangeM ± SD (95% CI)N
Years since PSO diagnosis0–7124.0 ± 15.33620–7920.7 ± 15.11526< 0.001*0–7921.3 ± 15.21890
 (22.5–25.6)  (19.9–21.5)   (20.6–22.0) 
Only if have been unfit in the past 12 months due to PSO: days unfit for work2–36538.1 ± 63.2442–20023.5 ± 27.81130.142–36527.6 ± 41.3 157
 (18.9–57.3)  (18.3–28.6)   (21.1–34.1) 
Only if hospitalized for PSO in past year: number of admissions1–212.7 ± 3.11331–302.5 ± 3.72490.551–302.6 ± 3.5 382
 (2.2–3.3)  (2.0–3.0)   (2.2–2.9) 

When the decision tree described in the Methods section was used for patients with suspected PsA (Fig. 1), it showed that PsA was present or probably present in 19% of patients. This was already known in the case of 14.8%, while in 4.2% it was diagnosed for the first time during the study. In 7.7%, the diagnosis of arthritis remained unclear (Table 3). No PsA was present in 73.2% of patients.

Table 3.  Psoriatic arthritis (PsA; n = 2.007)
 N%
PsA not present147073.2
PsA uncertain 154 7.7
PsA probable  85 4.2
PsA present 29814.8

Almost all patients (98.6%) who currently or previously reported joint symptoms and in whom PsA had not been confirmed showed at least one of the diagnostic criteria. Most frequently, this consisted of joint pain of more than 6 weeks’ duration (52.5%). In contrast, dactylitis (7.1%) and enthesitis (10.7%) occurred comparatively rarely (Table 4). The more frequently the six diagnostic criteria for PsA were met, the more likely it was that a doctor considered PsA to be present (Table 5).

Table 4.  Diagnostic information on psoriatic arthritis (n = 346 patients with joint symptoms, but without psoriatic arthritis diagnosis)
 Yes (%)No (%)Missing (n)
1. In the past 5 years, has the patient repeatedly had episodes of joint pain that lasted more than 6 weeks?52.547.5 5
2. Has swelling of the joints repeatedly occurred in the past 12 months?29.270.8 7
3. Has morning stiffness of the joints, that improved over the course of the day, repeatedly occurred in the past 12 months?37.162.9 6
4. In particular, has pain of the distal interphalangeal joints of the fingers repeatedly occurred in the past 12 months?26.873.2 6
5. Enthesitis: Has pain repeatedly occurred at the tendon insertions, particularly of the Achilles tendons or plantar aponeuroses, in the past 12 months?10.789.3 9
6. Dactylitis: Has painful swelling of an entire finger or toe repeatedly occurred in the past 12 months? 7.192.9 9
Was at least one of the questions (1) to (6) answered with ‘yes’?98.6 1.4 
 If yes (n = 341): Is diagnostic investigation of the psoriatic arthritis planned?54.445.621
 If investigation is planned (n = 174): Which tests/procedures are to be used?    
  Own clinical diagnosis37.362.7 
  X-ray/scan54.545.5 
  Rheumatological investigation64.235.8 
  Laboratory diagnostic tests19.480.6 
 ProbableUncertainRuled out
How do you currently assess the diagnosis of psoriatic arthritis? (missing: n = 64)27.044.029.1
Table 5.  Diagnostic information on psoriatic arthritis subject to psoriatic arthritis diagnosis (n = 2007)
PsA is ...Present (n = 298)Probable (n = 85)Uncertain (n = 154)Ruled out (n = 1470)
Yes (%)Yes (%)Yes (%)Yes (%)
Missing: n = 215–217*Missing: n = 0–1Missing: n = 0–3Missing: n = 1053–1061*
  • *

    The number of missing data is so high here because, according to instructions in the questionnaire, the diagnostic questions were only to be answered if ‘joint symptoms are present’ and diagnosis of psoriatic arthritis (PsA) is still uncertain. The values are therefore based on those patients for whom the PsA diagnosis was made contrary to the instruction.

  • The number of missing data is so high here because, according to instructions in the questionnaire, the PsA activity and the painful/swollen joints were only to be specified ‘if PsA is present’.

1. Joint pain89.075.056.511.5
2. Joint swelling65.454.131.85.5
3. Morning stiffness71.172.934.67.3
4. Distal interphalangeal joints symptoms64.653.631.63.4
5. Enthesitis20.722.68.61.7
6. Dactylitis30.516.57.20.7
 M ± SDM ± SDM ± SDM ± SD
Missing: n = 24Missing: n = 29Missing: n = 70Missing: n = 1404
Activity of the psoriatic arthritis (VAS 0–10)3.3 ± 2.53.2 ± 2.02.1 ± 1.80.9 ± 1.9
 M ± SDM ± SDM ± SDM ± SD
Missing: n = 23Missing: n = 22Missing: n = 61Missing: n = 1347
Number of painful joints7.4 ± 7.27.2 ± 7.64.0 ± 4.60.9 ± 2.5
Number of swollen joints3.6 ± 5.72.4 ± 5.21.0 ± 2.60.2 ± 1.1

Further diagnostic investigation was planned for more than half (54.4%) of the patients who met one of the criteria, especially by means of referral to a rheumatologist (64.2%) or an X-ray/scan (54.5%).

Information concerning the current joint status was available for 338 patients (16.8%). Two hundred and eighty-seven of the 338 patients (84.9%) suffered from at least one painful joint and 168 (49.7%) from at least one swollen joint. On average, the patients affected by pain indicated 8.7 ± 7.1 painful joints out of a possible 28 (maximum 28, median 6). The number of swollen joints in the patients affected by swelling averaged 6.8 ± 6.3 (maximum 28, median 4).

Depending on the joint, 20.1–27.8% of patients had pain in the arms; swelling occurred here in 2.7–8.3%. The right hand was most affected. About 40% of patients suffered from pain in the knees; 13.9–14.8% reported they had swollen knees. Depending on the joint, 19.2–35.8% of patients suffered from pain in the fingers. Swelling affected 10.4–20.1%; the most frequently affected joint in terms of both pain and swelling was the upper index finger joint of the right hand.

On a scale of 0 (inactive) to 10 (highly active), the average current activity of PsA was 3.3 ± 2.4 (minimum 0, maximum 10, median 3.0; n = 320) (Table 6).

Table 6.  Current activity of the psoriatic arthritis (scale from 0 = inactive to 10 = highly active) (n = 338)
 N%
03410.6
14112.8
26720.9
35717.8
4288.8
53210.0
6226.9
7154.7
8165.0
9 51.6
10 30.9
Missing18 

Discussion

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

The aim of the present study was to determine the prevalence and clinical spectrum of PsA in a sample of 2009 psoriasis patients in Germany. PsA was diagnosed on the strength of the typical pattern of complaints and symptoms or – in the case of a previous diagnosis – on the basis of the GRAPPA criteria. According to the analysis of the epidemiological data, 19% of the patients with psoriasis had a probable or confirmed PsA. In a further 7.7% of patients, the presence of PsA was uncertain.

These data do not completely support previous studies in which a lower proportion of psoriasis patients were diagnosed as having PsA.2–6 However, in the study by Gelfand et al., patients with psoriasis were identified from the general population with a potentially lower average disease severity6 compared to the patients referred to the dermatologist in this study. In addition, it is clear that a relatively large proportion of patients (n = 346) in whom joint symptoms exist had not previously been diagnosed with PsA. More than half of these patients said that they had repeatedly suffered in the past 5 years from episodes of pain that had lasted for more than 6 weeks. In the past 12 months, 37.1% had suffered frequently from morning stiffness of the joints and 29.2% reported recurrent swelling. Taken together, these symptoms are clear indications of the possible presence of PsA in patients already known to have psoriasis vulgaris, and should have alerted the respective doctors to initiate an appropriate diagnostic investigation. These data indicate that an early diagnosis of PsA and, with it, the prerequisite for a prompt initiation of treatment, does yet not happen for a considerable proportion of patients.

The limitations of the present study lie in the fact that, even today, the diagnostic criteria for PsA vary considerably and that a firm clinical diagnosis cannot be made in some individual cases. Due to the cross-sectional character of the present study, further diagnostic procedures needed for confirmation of diagnosis could not be considered. The inclusion of other interdisciplinary measures was also not possible, which explains the high percentage of (7.7%) diagnoses that were still unclear. The figure for probable or confirmed diagnoses (19%) therefore represents a somewhat conservative estimate. Both in the anamnestic characteristics of the PsA and in the status of the joint, this percentage of patients showed quite high rates of fulfilment of GRAPPA criteria which underlines the validity of the present approach involving anamnestic screening and subsequent evaluation of the status of the joint.

The ‘best pathway’ of diagnostic confirmation in PsA is still controversial and under discussion.18 For this, a stringent recommendation cannot be given at this point. The present data, however, indicate that the clinical parameters chosen (joint pain, joint swelling, morning stiffness, distal interphalangeal joint symptoms, enthesitis and dactylitis) are of substantial value in the screening of potential PsA patients. Once screened positively, any patient needs further work-up, including laboratory tests and radiological investigation.

Many investigations have shown that there is a discrepancy between the currently available therapies for the treatment of psoriasis and PsA and the ease of access for affected patients to these treatment options.5,21–24 The early, correct and sustainable diagnosis of PsA is the basis for treatment. For dermatologists, this means the urgent need to develop an appropriate awareness of this disease. Since most patients (approximately 80%) initially show skin symptoms, dermatologists, in particular, should look out for joint symptoms and familiarize themselves with the heterogeneous spectrum and possible clinical manifestations. Conversely, awareness ought to be established among rheumatologists and orthopaedic specialists that the presence of skin symptoms is not absolutely necessary for the diagnosis of PsA (in 10% of patients, the joint manifestation precedes the skin changes). This knowledge will enable them to correctly classify already verifiable changes to bones, joints and ligaments in conjunction with the corresponding symptoms and complaints. For many patients suffering from skin and joint symptoms, treatment will also be established on an interdisciplinary basis in addition to an interdisciplinary approach to diagnosis. To improve the quality of care of patients with PsA, the further development of indicators of the quality of care will be necessary in the future.

Acknowledgement

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References

This project was supported by a research grant from Wyeth.

References

  1. Top of page
  2. Introduction
  3. Objective
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. References
  • 1
    Gladman D, Mease P, Krueger G et al . Outcome measures in psoriatic arthritis. J Rheumatol 2007; 34: 11591166.
  • 2
    Alamanos Y, Voulgari PV, Drosos AA. Incidence and prevalence of psoriatic arthritis: a systematic review. J Rheumatol 2008; 35: 13541358.
  • 3
    Espinoza LR, Cuéllar ML, Silveira LH. Psoriatic arthritis. Curr Opin Rheumatol 1992; 4: 470478.
  • 4
    Golfieri R, Giampalma E, Tosti A, Calculli L, Berardi R, Gavelli G. Psoriasis arthropathica. A review of the literature, general considerations and the authors’ personal experience.] Radiol Med 1992; 84: 228235 (in Italian).
  • 5
    Gisondi P, Girolomoni G, Sampogna F, Tabolli S, Abeni D. Prevalence of psoriatic arthritis and joint complaints in a large population of Italian patients hospitalised for psoriasis. Eur J Dermatol 2005; 15: 279283.
  • 6
    Gelfand JM, Gladman DD, Mease PJ, Smith N, Margolis DJ, Nijsten T, Stern RS, Feldman SR, Rolstad T. Epidemiology of psoriatic arthritis in the population of the United States. J Am Acad Dermatol 2005; 53: 573.
  • 7
    Ackermann C, Kavanaugh A. Economic burden of psoriatic arthritis. Pharmacoeconomics 2008; 26: 121129.
  • 8
    Taylor WJ. Epidemiology of psoriatic arthritis. Curr Opin Rheumatol 2002; 14: 98103.
  • 9
    Helliwell PS, Taylor WJ. Classification and diagnostic criteria for psoriatic arthritis. Ann Rheum Dis 2005; 64 (Suppl. 2): ii38.
  • 10
    Gladman DD. Psoriatic arthritis. Baillieres Clin Rheumatol 1995; 9: 319329.
  • 11
    Vasey F, Espinoza LR. Psoriatic arthropathy. In: CalinA, eds. Spondylarthropathies. Grune & Stratton, Orlando, FL, 1984: 151185.
  • 12
    Dougados M, Van Der Linden S, Juhlin R et al . The European Spondylarthropathy Study Group preliminary criteria for the classification of spondylarthropathy. Arthritis Rheum 1991; 34: 12181227.
  • 13
    Bennett RM. Psoriatic arthritis. In: McCartyDJ, ed. Arthritis and Related Conditions: A Textbook of Rheumatology. Lea & Febiger, Philadelphia,1979: 645.
  • 14
    Chandran V, Schentag CT, Gladman DD. Are the CASPAR Criteria for psoriatic arthritis accurate when applied to patients attending a family practice clinic? Arthritis Rheum 2006; 54: 4091.
  • 15
    Moll JM, Wright V. Psoriatic arthritis. Semin Arthritis Rheum 1973; 3: 5578.
  • 16
    Brockbank J, Stein M, Schentang C, Gladman DD. Dactylitis in psoriatic arthritis: a marker for disease severity? Ann Rheum Dis 2005; 64: 188190.
  • 17
    Vyse TJ, Todd JA. Genetic analysis of autoimmune disease. Cell 1996; 85: 311318.
  • 18
    Kavanaugh A, Ritchlin C, Boehncke WH. Quality indicators in psoriatic arthritis. Clin Exp Rheumatol 2007; 25 (6 Suppl. 47): 98101.
  • 19
    Gladman DD, Mease PJ, Healy P et al . Outcome measures in psoriatic arthritis. J Rheumatol 2007; 34: 11591166.
  • 20
    Gladman DD, Mease PJ, Krueger G et al . Outcome measures in psoriatic arthritis. J Rheumatol 2005; 32: 22622269.
  • 21
    Krueger G, Koo J, Lebwohl M, Menter A, Stern RS, Rolstad T. The impact of psoriasis on quality of life: results of a1998 National Psoriasis Foundation patient-membership survey. Arch Dermatol 2001; 137: 280284.
  • 22
    Dubertret L, Mrowietz U, Ranki A et al . European patient perspectives on the impact of psoriasis: the EUROPSO patient membership survey. Br J Dermatol 2006; 155: 729736.
  • 23
    Berger K, Ehlken B, Kugland B, Augustin M. Cost-of-illness in patients with moderate and severe chronic psoriasis vulgaris in Germany. J Dtsch Dermatol Ges 2005; 3: 511518.
  • 24
    Sohn S, Schoeffski O, Prinz J, Reich K, Schubert E, Waldorf K, Augustin M. Cost of moderate to severe plaque psoriasis in germany: a multicenter cost-of-illness study. Dermatology 2006; 212: 137144.