Objectives The objectives of this study were to: (1) assess the prevalence of psoriatic arthritis (PsA) among Psoriasis (Ps) patients attending dermatology clinics; (2) identify clinical predictors of the development of PsA; and (3) compare the performance of three PsA screening questionnaires: Psoriatic Arthritis Screening and Evaluation (PASE), Psoriasis Epidemiology Screening Tool (PEST) and Toronto Psoriatic Arthritis Screening (ToPAS).
Methods Patients were divided into two groups: Group-1, consecutive psoriasis patients attending dermatology clinics with no known diagnosis of inflammatory arthritis and Group-2, consecutive patients attending rheumatology clinics with a confirmed diagnosis of PsA. In Group-1, patients completed the screening questionnaires, followed by a full rheumatological evaluation whether or not they reported musculoskeletal symptoms.
Results 200 patients were recruited with 100 in each group. In all, 84% of patients in dermatology group were using systemic therapy for their skin disease, and 99% of patients in rheumatology group were on systemic immunosuppressives. In Group-1, 29% of patients were diagnosed with PsA after rheumatological evaluation. On univariate and multivariate analyses, there was a significant positive association between Psoriasis Area and Severity Index and a new diagnosis of PsA (p=0.046). Different patterns of joint involvement were noted in patients with newly diagnosed PsA versus patients with established PsA with fewer polyarticular disease presentations (p=0.0001). In Group-1, the PEST, PASE and ToPAS assessments had sensitivities of 27.5%, 24% and 41%, and specificities of 98%, 94% and 90%, respectively. In Group-2, the sensitivities were 86%, 62% and 83%, respectively.
Conclusions 29% of Ps patients attending dermatology clinics had undiagnosed PsA. Psoriasis severity was associated with a new diagnosis of PsA. Poor sensitivities for the screening questionnaires were noted due to inadequate detection of patterns of arthritis other than polyarticular disease.
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Psoriatic arthritis (PsA) is a progressive inflammatory joint disease, causing pain and joint damage eventually leading to disability. Up to 47% of patients develop erosive changes within 2 years of disease onset.1 There are varied reports of its prevalence among patients with psoriasis, with the prevalence rates ranging from 6% to 42%.2 The severity of psoriasis has been regarded as a poor clinical predictor of the development and severity of PsA;2 however, a recent report has suggested the opposite results.3
Similar to patients with rheumatoid arthritis, early diagnosis and institution of disease modifying antirheumatic drug treatment have been shown to have an impact on long-term morbidity.4 The delay in the diagnosis of PsA however remains a significant contributor to poor patient outcomes (online supplementary appendix). The early identification of patients with PsA among patients with psoriasis therefore assumes considerable importance. Patients with psoriasis are usually managed by general practitioners or by dermatologists who can either rely on self-reported joint symptoms to identify PsA or can be more proactive in elucidating the appropriate musculoskeletal (MSK) symptoms and signs. Both approaches present difficulties with patients failing to appreciate the relevance of their symptoms and time constraints on general practitioners and dermatologists that hinder appropriate assessment. It is neither appropriate nor practical to seek rheumatologist opinion for all psoriasis patients in order to assess for the development of PsA. Screening questionnaires have been developed as referral tools to help dermatologists and general practitioners identify suitable individuals for referral to rheumatologists. These screening tools include the Psoriatic Arthritis Screening and Evaluation (PASE), Psoriasis Epidemiology Screening Tool (PEST) and the Toronto Psoriatic Arthritis Screening (ToPAS).5–8 As these are not diagnostic tools, individuals identified by such screening tools as likely candidates must then undergo further rheumatological evaluation in order that a definitive diagnosis can be made. The screening tools have undergone initial validation at the centres where they were developed with some additional validation being provided in subsequent studies.5–10 To our knowledge, sensitivity and specificity of these tools versus the gold standard of a full rheumatological evaluation has not been compared in psoriasis patients attending dermatology clinics.
The aims of this study were threefold: (1) to assess the prevalence of undiagnosed PsA among patients attending dermatology clinics, (2) to explore the impact of demographics and different disease specific characteristics on the development of PsA and (3) to compare the performance and utility of the three PsA questionnaires (PASE, PEST, and the ToPAS) versus a full rheumatological evaluation using CASPAR criteria (Criteria of the ClASsification of Psoriatic ARthritis) in psoriasis patients attending dermatology clinics.
This study was carried out in the general dermatology and rheumatology clinics based at St. Vincent's University Hospital, Dublin, Ireland. We divided patients into two groups: Group-1, patients with skin psoriasis attending dermatology clinics who have no known diagnosis of arthritis and Group-2, patients attending rheumatology clinic with a confirmed diagnosis of PsA as per the internationally agreed CASPAR criteria.11 All consecutive psoriasis patients attending dermatology clinics, but who did not have a diagnosis of PsA, were suitable for inclusion. Consecutive patients attending rheumatology clinics with a confirmed diagnosis of PsA were also eligible to partake. Patients with a concomitant MSK condition, such as osteoarthritis, gout and fibromyalgia, were not excluded in both dermatology and rheumatology groups, but we did exclude those patients with a history of other inflammatory arthropathies, such as rheumatoid arthritis.
The study was approved by the Medical Research Ethics committee of St. Vincent's University Hospital. Informed written consent was obtained from patients before inclusion in the study (Methods have been described in more detail in the online supplementary appendix). The assessment of psoriatic patients enrolled in Group-1 was carried out in two steps. The first step involved completing the questionnaires (PEST, PASE, ToPAS), and documentation of the following clinical details: demographics, therapies used for psoriasis, duration of skin disease, presence of nail involvement, and the extent and severity of skin psoriasis as reflected by the Psoriasis Area and Severity Index (PASI), which is the most widely used tool for the measurement of severity of psoriasis. In the second step, all patients received a full rheumatological evaluation, whether or not they reported any MSK symptoms. The rheumatological parameters evaluated included joint counts (tender, swollen, damaged), entheseal counts using the Leeds Enthesitis Index and including evaluation of the plantar fascia insertion, dactylitic counts and history taking and examination for axial inflammatory joint disease. The final diagnosis of PsA in Group-1 was made by the fulfilment of CASPAR classification criteria (online supplementary appendix). To observe the pattern of initial presentation and to compare this with the group of established PsA patients, we categorised PsA patients into four main categories depending on the predominant type of arthritis. These categories include: polyarthritis (≥5 joints affected), oligoarthritis (≤4 joints affected), predominant entheseal involvement and predominant inflammatory axial involvement. The questionnaires were not marked prior to rheumatological assessment, and hence, the rheumatologist assessing these psoriatic patients was unaware of the results of questionnaires. Questionnaires were marked and scored for questionnaire positivity or negativity. For this study, previously established cut-off scores were used to designate positive and negative results for each screening tool. The sensitivities and specificities of these questionnaires were determined by comparing the results with the rheumatological diagnostic assessment using CASPAR criteria.
Statistical analysis was performed using the SPSS software, V.17. Significance was defined as p<0.05 (two-tailed). A χ2 statistic was used to investigate the distributions of categorical variables, and continuous variables were analysed using Student t test. The association among psoriasis extent, duration of psoriasis, nail disease, therapies used for psoriasis, use of TNFi (Tumour necrosis Factor inhibitors), age and sex with newly diagnosed PsA was determined by using univariate and multivariate logistic regression.
The efficacy of screening tools in predicting a diagnosis of PsA was measured in terms of sensitivity and specificity. Sensitivity indicates the probability that someone with PsA would have tested positive on these questionnaires; specificity refers to the probability that someone without PsA would have tested negative on these questionnaires. Positive predictive value and negative predictive value were also determined, which reflect the probability of how likely a patient with a positive or negative test result actually has or does not have the particular disease.
In all, 200 patients were recruited of whom 100 were from the dermatology clinics (Group-1) and 100 were from the rheumatology clinics (Group-2). Table 1 illustrates the demographic details and clinical characteristics of these two groups. It was noted that Group-1 patients had significantly more severe psoriasis (PASI), more scalp psoriasis at the time of assessment and less nail disease ever in the disease course compared with Group-2. In all, 84% of patients in dermatology group were using systemic therapy for their skin disease, and 99% of patients in rheumatology group were on systemic immunosuppressives.
In Group-1, 29% of patients were diagnosed with PsA after rheumatological evaluation (Results have been described in more detail in the results section of online supplementary appendix). Table 2 compares the demographic and clinical details of these newly diagnosed PsA patients with those who had no PsA. This subgroup analysis revealed that newly diagnosed PsA patients had more severe psoriasis as measured by PASI. There was no significant difference as regards age, gender, medications used for psoriasis, duration of skin psoriasis and nail disease. We also compared the clinical characteristics of newly diagnosed PsA patients with the established PsA patients of Group-2 (table 3). This revealed that the pattern of joint involvement was significantly different with less polyarticular disease in newly diagnosed PsA patients.
On univariate and multivariate analyses, the only significantly positive association was noted between PASI and the new diagnosis of PsA (OR 1.45 (95% CI 1.00 to 2.11), p=0.05, and OR 1.61 (95% CI 1.06 to 2.44), p=0.02, respectively), even after adjusting for confounders such as age, gender, use of TNFi (Tumour Necrosis Factor inhibitor), duration of psoriasis and the presence of nail and scalp disease ever in the disease course (table 4).
Table 5 shows the sensitivity, specificity, positive predictive value and negative predictive value of the three screening questionnaires. In Group-1, the PEST, PASE and ToPAS had sensitivities of only 27.5%, 24% and 41%, respectively; however, the sensitivities of these three screening tools in Group-2 were 86%, 62% and 83%, respectively. We also looked at the sensitivity and specificity of lower cut-off points for each questionnaire (online supplementary appendix). We also examined whether these questionnaires differ in their performance depending on the subtype of arthritis present. This analysis showed that the PEST and ToPAS questionnaires had comparatively better sensitivities in identifying PsA patients with polyarticular involvement (77% and 88%. respectively), but their sensitivities were low for any other non-polyarticular disease presentations (5% and 20%, respectively). The PASE questionnaire had poor performance for both polyarticular and non-polyarticular disease (sensitivity of 22% and 20%, respectively) (table 6).
The delay in the diagnosis of PsA remains a significant contributor to poor patient outcome thus highlighting the need to improve our evaluation of patients who are at risk for articular disease. The results of our study are important in a number of ways. First, we found that after excluding patients with known PsA, 29% of psoriasis patients attending dermatology clinics had undiagnosed PsA. These prevalence rates are significantly higher than in previous reports, which reveal undiagnosed PsA in 17%, and both diagnosed and undiagnosed PsA in 30%.12 ,13 Second, we noted also that severity of skin disease is independently associated with the development of PsA. Our study was carried out in a routine dermatology clinical setting, where the majority of psoriasis patients being followed used systemic therapies. It was surprising to note such a high prevalence of PsA since a significant numbers of patients were already using TNFi (Tumour Necrosis Factor inhibitor) and disease modifying antirheumatic drugs, which are treatments of choice for PsA and may have masked the development of articular involvement. It is possible that in the absence of such therapies, the prevalence of PsA would have been higher (online supplementary appendix). In our cohort, when we compared the extent of skin involvement of newly diagnosed PsA patients with those who had no PsA in Group-1, the PASI was significantly higher in newly diagnosed patients with PsA. We investigated this further by using univariate and multivariate regression models and noted that psoriasis severity was an independent predictor of undiagnosed PsA among psoriasis patients after adjusting for all factors in the model which included age, gender, use of TNFi (Tumour Necrosis Factor inhibitor), duration of psoriasis and the presence of nail and scalp disease ever in the disease course.
Third, and consistent with previous reports,14–16 we found that the presence of psoriatic nail disease ever in the disease course was significantly higher in established PsA patients (Group-2) versus Group-1 (p=0.041). A trend was also seen in newly diagnosed PsA patients with a non-significant association when compared with those who had no PsA (p=0.065). The presence of nail disease at the time of assessment was not statistically different among all cohorts: Group-1 versus Group-2, or newly diagnosed PsA patients versus those who had no PsA in Group-1. It is possible that the use of systemic therapies which may be effective for nail psoriasis is an explanation for this observation. It should be noted that the CASPAR criteria only accept nail disease if evident on current physical examination. The screening questionnaire PEST attributes a fifth of its total score if a patient has current nail changes.8
Fourth, the presence of scalp disease ever in the disease course was found to be statistically similar in all cohorts. When compared with Group-2, Group-1 patients had higher incidence of scalp psoriasis at the time of assessment, probably reflecting more severe psoriasis. In contrast to previous reports,15 ,16 there was no difference in the prevalence of current scalp psoriasis between Group-1 patients with newly diagnosed PsA and those with psoriasis only.15 ,16
Finally, our study showed poor sensitivities for the three screening questionnaires for PsA. This observation is of importance as PsA is no longer considered as a mild form of arthritis. In one study, 67% of PsA patients demonstrated ≥1 radiographic erosion at their initial presentation to a rheumatologist.17 In an inception cohort study, Kane et al1 found that 47% of their patients with early arthritis who presented within 5 months of onset of symptoms had ≥1 erosion by the second year of follow-up. These study results have important implications for the use of these instruments for screening purposes (online supplementary appendix). It would appear that the questionnaires in particular performed poorly in identifying patients with non-polyarticular presentations of PsA. Modification of the current questionnaires or development of a new questionnaire to reflect these observations is required if these screening tools are to be useful in identifying early PsA among the large population of psoriasis patients. We believe that the main thrust and focus of screening tools should be in dermatology clinics as dermatologists assess and treat patients with more severe psoriasis who are at risk for developing PsA.
The strengths of our study include the following: (1) to reduce the possible confounding effect of differences in access to healthcare services, this study was carried out in one secondary care dermatology/rheumatology setting; (2) to minimise the selection bias, we have attempted to recruit all consecutive patients; and (3) to standardise the study procedures, all patients were reviewed by a single, trained rheumatologist. We acknowledge there are some limitations to our study. For example, we did not include other known risk factors for psoriasis and PsA, such as body mass index, presence of psoriasis at intergluteal regions and alcohol consumption. No data were collected on the functional impairment of both groups. x-Rays were requested only in suspected cases of PsA; however, no imaging studies were used to confirm the clinical diagnosis of enthesopathies. In addition, our study population was receiving systemic therapy for their psoriasis, which could potentially limit the generalisability of results to a more severe spectrum of psoriatic disease.
Our study confirms the high prevalence of PsA in patients with psoriasis with severity of skin involvement as a useful predictor. Poor sensitivity performance of the three available screening tools was also observed. Improving the identification of the predictors of PsA development and devising an effective screening questionnaire would aid in the earlier diagnosis and improving long-term patient outcome.
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Contributors MH carried out the work, collection and interpretation of data and manuscript drafting. BK and OF conceived the study, its design, coordination, data interpretation and manuscript drafting and editing.
Competing interest None.
Patient consent Obtained.
Ethics approval Ethics approval provided by the St. Vincent's Healthcare Group, Ethics and Medical Research Committee.
Provenance and peer review Not commissioned; externally peer reviewed.
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