Skin psoriasis is a major risk factor for the development of psoriatic arthritis. Recent studies have shown that delayed diagnosis is associated with long-term adverse outcomes. Screening questionnaires have revealed a potential burden of undiagnosed disease. Lifestyle factors and genetic and soluble biomarkers have come under scrutiny as risk factors. Imaging modalities may have an important role in detecting early change. With more effective treatments, it may be possible to prevent significant joint damage and associated disability. However, the precise nature of accurate and cost-effective screening strategies remains to be determined.
Key points
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Early psoriatic arthritis is a heterogeneous condition that can make diagnosis difficult and can be confused with nodal osteoarthritis, fibromyalgia, and mechanical back pain.
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Screening questionnaires have highlighted that a significant number of cases are undiagnosed and delay in diagnosis may be associated with poorer long-term outcome.
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Currently, the strongest predictors for the development of psoriatic arthritis in individuals with psoriasis are nail disease, obesity, and HLA-B27.
Introduction
Psoriatic arthritis is a heterogeneous condition that may present in several different patterns; therefore, diagnosis and differentiation from other forms of arthritis can often be a challenge. Unlike conditions such as rheumatoid arthritis, systemic lupus erythematosus, or systemic vasculitis, there are no autoimmune diagnostic markers. Furthermore, once diagnosed the future course may be unpredictable and there is a relative paucity of known risk factors or biomarkers that reliably predict long-term outcome. Although there are several national and international guidelines that help to guide treatment for patients with persistently active disease, such as those who would benefit from biological therapy, there is less information to guide management of the patient with early or recently diagnosed disease. Yet the most frequently asked question from patients newly diagnosed with psoriatic arthritis relates to future outcome.
We now recognize that psoriatic arthritis is not a benign condition and, with more effective treatments available, there may never be a better opportunity for preventing its development from an early stage. Skin psoriasis precedes the development of psoriatic arthritis in the majority of cases and so represents an excellent opportunity for implementing screening strategies. Some of the evidence for the important of early detection is reviewed, as are recent epidemiologic findings, the development of screening questionnaires, and identification of high-risk groups in whom screening should be applied. With the advent of more effective treatment than traditional agents, there has never been such an urgent need to focus much more attention on the natural history of early disease.
Is Psoriatic Arthritis Underdiagnosed?
There have been variable estimates of the incidence and prevalence of psoriatic arthritic, likely owing to factors such as historical differences in diagnostic criteria applied, study setting, and method of case ascertainment. Although a systematic review reported a median incidence of 6.4 in 100,000 cases per year of psoriatic arthritis in the general population, a more recent population-based study from Norway found 188 incident cases over an 8-year period giving an incidence rate of 41.3 in 100,000. Studies of psoriasis using information from clinical records reported a 10-year cumulative incidence of 3.1%, whereas a prospective cohort study of psoriasis found an incidence of 1.8%.
However, both the incidence and prevalence are likely to be higher; studies using screening questionnaires revealed that many patients are undiagnosed. For instance, 10.9% of patients from dermatology clinics in Germany were identified with undiagnosed psoriatic arthritis as were 29% in a study from Dublin. In a German study from 48 centers studying 1511 patients with psoriasis, 21% had psoriatic arthritis and as many as 85% of cases were newly diagnosed after assessment by rheumatology. In another multinational study of 34 dermatology centers, 949 patients with plaque psoriasis were evaluated and 41% of 285 with psoriatic arthritis had not previously been diagnosed. From a large, population-based, telephone survey of households in North America and Europe, 44% of patients with a diagnosis of psoriasis alone reported joint pain. However, the importance of earlier detection remains uncertain because the natural history of undiagnosed psoriatic arthritis is unknown.
Observational Studies of Outcome in Psoriatic Arthritis
Long-term observational studies of psoriatic arthritis such as those from the Toronto cohort and elsewhere have provided valuable information on the natural history. For instance, health-related quality of life measures are similar to rheumatoid arthritis. There are important comorbidities such as dyslipidemia and premature atherosclerosis. In 1 study of early psoriatic arthritis, joint erosions were present in 27% of patients at 10 months and in 47% of patients within 2 years of disease onset. Peripheral joint disease is progressive in the majority of patients with the highest rate of progression in the first year of disease.
Several more recent studies also suggest that delay in diagnosis is associated with a worse outcome. In the Toronto cohort, those patients first seen after 2 years of diagnosis compared with those seen within 2 years had a greater rate of joint damage. In our own Bath cohort, delay in diagnosis as well as smoking, female gender, and older age at onset were associated with a worse physical function measured by the Health Assessment Questionnaire after 10 years. Similar observations were reported in a Dublin cohort with late consulters having greater peripheral joint erosion and worse physical function. Finally, results from the Swedish Early Psoriatic Arthritis Register showed that shorter duration of symptoms and lower Health Assessment Questionnaire scores independently predicted achievement of a state of minimal disease activity at 5 years. Therefore, indirect evidence suggests that early intervention may be important in decreasing the burden of disease.
Some further evidence in support of early intervention comes from clinical trials. In the PRESTA, study patients receiving etanercept 50 mg once weekly with psoriatic arthritis for less than 2 years had greater improvement in efficacy measures than those with longer disease duration.
Detection of Early Disease
The development of the CASPAR classification criteria helped to standardize the characteristics of patients in cohort studies and entry into clinical trials. CASPAR also performs well in patients with early psoriatic arthritis. However, CASPAR is mainly designed for use in rheumatology settings; therefore, other mechanisms for identifying patients with psoriatic arthritis are required.
Screening questionnaires
Several questionnaires were developed by different groups to screen for patients with psoriatic arthritis in various settings. Studies to compare the performance of the questionnaires were reported, such as 2 comparing the Psoriatic Arthritis Screening Evaluation (PASE), the Toronto Psoriatic Arthritis Screen (ToPAS), and the Psoriasis Epidemiology Screening Tool (PEST), and another the Psoriasis and Arthritis Screening Questionnaire (PASQ) with ToPAS and PEST. In general, the screening tools have not performed as well as in the setting where they were derived, although they have identified both undiagnosed psoriatic arthritis and patients who may benefit from rheumatology review. More recently, another questionnaire (CONTEST) was derived combining optimal questions from existing tools and requires further evaluation. The efficacy of screening questionnaires in various health care settings, including the frequency of use and characteristics of the target population to which they are applied still, remains to be determined.
Imaging
Imaging modalities such as ultrasonography have the potential for detecting preclinical disease. Gisondi and colleagues demonstrated entheseal abnormalities by ultrasonography in clinically asymptomatic patients with psoriasis. Power Doppler ultrasonography may detect vascular changes that herald the development of arthritis. Also of much interest, psoriasis patients with nail changes demonstrated higher enthesitis scores at remote sites than patients with normal nails, consistent with observations that patients with psoriatic arthritis have a greater frequency of nail disease than psoriasis patients alone. MRI may reveal subclinical synovitis and enthesitis inpatients with psoriasis without arthritis symptoms.
Ultrasonography may also be helpful with good specificity for documenting joint and tendon involvement in early psoriatic arthritis. Furthermore, persistent change on gray scale or power Doppler ultrasonography may be a risk factor for disease progression.
Introduction
Psoriatic arthritis is a heterogeneous condition that may present in several different patterns; therefore, diagnosis and differentiation from other forms of arthritis can often be a challenge. Unlike conditions such as rheumatoid arthritis, systemic lupus erythematosus, or systemic vasculitis, there are no autoimmune diagnostic markers. Furthermore, once diagnosed the future course may be unpredictable and there is a relative paucity of known risk factors or biomarkers that reliably predict long-term outcome. Although there are several national and international guidelines that help to guide treatment for patients with persistently active disease, such as those who would benefit from biological therapy, there is less information to guide management of the patient with early or recently diagnosed disease. Yet the most frequently asked question from patients newly diagnosed with psoriatic arthritis relates to future outcome.
We now recognize that psoriatic arthritis is not a benign condition and, with more effective treatments available, there may never be a better opportunity for preventing its development from an early stage. Skin psoriasis precedes the development of psoriatic arthritis in the majority of cases and so represents an excellent opportunity for implementing screening strategies. Some of the evidence for the important of early detection is reviewed, as are recent epidemiologic findings, the development of screening questionnaires, and identification of high-risk groups in whom screening should be applied. With the advent of more effective treatment than traditional agents, there has never been such an urgent need to focus much more attention on the natural history of early disease.
Is Psoriatic Arthritis Underdiagnosed?
There have been variable estimates of the incidence and prevalence of psoriatic arthritic, likely owing to factors such as historical differences in diagnostic criteria applied, study setting, and method of case ascertainment. Although a systematic review reported a median incidence of 6.4 in 100,000 cases per year of psoriatic arthritis in the general population, a more recent population-based study from Norway found 188 incident cases over an 8-year period giving an incidence rate of 41.3 in 100,000. Studies of psoriasis using information from clinical records reported a 10-year cumulative incidence of 3.1%, whereas a prospective cohort study of psoriasis found an incidence of 1.8%.
However, both the incidence and prevalence are likely to be higher; studies using screening questionnaires revealed that many patients are undiagnosed. For instance, 10.9% of patients from dermatology clinics in Germany were identified with undiagnosed psoriatic arthritis as were 29% in a study from Dublin. In a German study from 48 centers studying 1511 patients with psoriasis, 21% had psoriatic arthritis and as many as 85% of cases were newly diagnosed after assessment by rheumatology. In another multinational study of 34 dermatology centers, 949 patients with plaque psoriasis were evaluated and 41% of 285 with psoriatic arthritis had not previously been diagnosed. From a large, population-based, telephone survey of households in North America and Europe, 44% of patients with a diagnosis of psoriasis alone reported joint pain. However, the importance of earlier detection remains uncertain because the natural history of undiagnosed psoriatic arthritis is unknown.
Observational Studies of Outcome in Psoriatic Arthritis
Long-term observational studies of psoriatic arthritis such as those from the Toronto cohort and elsewhere have provided valuable information on the natural history. For instance, health-related quality of life measures are similar to rheumatoid arthritis. There are important comorbidities such as dyslipidemia and premature atherosclerosis. In 1 study of early psoriatic arthritis, joint erosions were present in 27% of patients at 10 months and in 47% of patients within 2 years of disease onset. Peripheral joint disease is progressive in the majority of patients with the highest rate of progression in the first year of disease.
Several more recent studies also suggest that delay in diagnosis is associated with a worse outcome. In the Toronto cohort, those patients first seen after 2 years of diagnosis compared with those seen within 2 years had a greater rate of joint damage. In our own Bath cohort, delay in diagnosis as well as smoking, female gender, and older age at onset were associated with a worse physical function measured by the Health Assessment Questionnaire after 10 years. Similar observations were reported in a Dublin cohort with late consulters having greater peripheral joint erosion and worse physical function. Finally, results from the Swedish Early Psoriatic Arthritis Register showed that shorter duration of symptoms and lower Health Assessment Questionnaire scores independently predicted achievement of a state of minimal disease activity at 5 years. Therefore, indirect evidence suggests that early intervention may be important in decreasing the burden of disease.
Some further evidence in support of early intervention comes from clinical trials. In the PRESTA, study patients receiving etanercept 50 mg once weekly with psoriatic arthritis for less than 2 years had greater improvement in efficacy measures than those with longer disease duration.
Detection of Early Disease
The development of the CASPAR classification criteria helped to standardize the characteristics of patients in cohort studies and entry into clinical trials. CASPAR also performs well in patients with early psoriatic arthritis. However, CASPAR is mainly designed for use in rheumatology settings; therefore, other mechanisms for identifying patients with psoriatic arthritis are required.
Screening questionnaires
Several questionnaires were developed by different groups to screen for patients with psoriatic arthritis in various settings. Studies to compare the performance of the questionnaires were reported, such as 2 comparing the Psoriatic Arthritis Screening Evaluation (PASE), the Toronto Psoriatic Arthritis Screen (ToPAS), and the Psoriasis Epidemiology Screening Tool (PEST), and another the Psoriasis and Arthritis Screening Questionnaire (PASQ) with ToPAS and PEST. In general, the screening tools have not performed as well as in the setting where they were derived, although they have identified both undiagnosed psoriatic arthritis and patients who may benefit from rheumatology review. More recently, another questionnaire (CONTEST) was derived combining optimal questions from existing tools and requires further evaluation. The efficacy of screening questionnaires in various health care settings, including the frequency of use and characteristics of the target population to which they are applied still, remains to be determined.
Imaging
Imaging modalities such as ultrasonography have the potential for detecting preclinical disease. Gisondi and colleagues demonstrated entheseal abnormalities by ultrasonography in clinically asymptomatic patients with psoriasis. Power Doppler ultrasonography may detect vascular changes that herald the development of arthritis. Also of much interest, psoriasis patients with nail changes demonstrated higher enthesitis scores at remote sites than patients with normal nails, consistent with observations that patients with psoriatic arthritis have a greater frequency of nail disease than psoriasis patients alone. MRI may reveal subclinical synovitis and enthesitis inpatients with psoriasis without arthritis symptoms.
Ultrasonography may also be helpful with good specificity for documenting joint and tendon involvement in early psoriatic arthritis. Furthermore, persistent change on gray scale or power Doppler ultrasonography may be a risk factor for disease progression.
Related posts:
The Epidemiology of Psoriatic Arthritis
Clinical Features and Diagnostic Considerations in Psoriatic Arthritis
Natural History, Prognosis, and Socioeconomic Aspects of Psoriatic Arthritis
Genetic, Epigenetic and Pharmacogenetic Aspects of Psoriasis and Psoriatic Arthritis
Outcome Measures in Psoriatic Arthritis
Biologic Therapy for Psoriatic Arthritis
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