SIGN Guideline 121: Diagnosis and management of psoriasis and psoriatic arthritis in adults

Guideline Index Page | SIGN Methodology | Summary of Recommendations

4 Diagnosis, assessment and monitoring



Diagnosis of cutaneous psoriasis is usually straightforward based on the clinical appearance (see for representative images). The most frequent presentation is chronic plaque psoriasis (psoriasis vulgaris) and is characterised by well demarcated bright red plaques covered by adherent silvery white scales. These may affect any body site, often symmetrically, especially the scalp and extensor surfaces of limbs. The differential diagnosis includes eczema, tinea, lichen planus and lupus erythematosus. The appearance of the plaques may be modified by emollients and topical treatments, which readily remove the scale. Scaling is reduced at flexural sites, on genital skin and in palmoplantar disease.

Guttate psoriasis describes the rapid development of multiple small papules of psoriasis over wide areas of the body. The differential diagnosis includes pityriasis rosea, viral exanthems and drug eruptions.

Generalised pustular psoriasis is rare and is characterised by the development of multiple sterile non-follicular pustules within plaques of psoriasis or on red tender skin. This may occur acutely and be associated with fever. The differential diagnosis includes pyogenic infection, vasculitis and drug eruptions.


Several clinical patterns of joint involvement in PsA have been identified including distal arthritis, asymmetric oligoarthritis (less than five joints), symmetric polyarthritis, arthritis mutilans, and spondyloarthritis (sacroiliitis and spondylitis). Patients often present with a mixture of subtypes and the pattern of disease may vary over time. The most frequent presentation is polyarthritis, followed by oligoarthritis. Other common features of PsA include enthesitis (inflammation at the tendon/bone interface), tenosynovitis and dactylitis (sausage digit).15 Inflammatory back pain is an important clinical symptom in patients with axial disease and the Assessment of SpondyloArthritis international Society (ASAS) criteria may be applied to these patients.

The ASAS criteria for inflammatory back pain are:

The criteria are fulfilled if four out of five parameters are present in patients who have had chronic back pain for more than three months. The criteria show a sensitivity of 77% and specificity of 91.7%.16


In the absence of a correct diagnosis, psoriasis and PsA may go untreated and may progress, potentially worsening the patient’s quality of life and prognosis.

No studies were identified to show whether early compared to late diagnosis and treatment of psoriasis or PsA alter long term outcome in terms of comorbidities, joint damage and disability.

One study showed that at two years, 47% of patients with PsA demonstrate joint erosions on X-ray.17 Two RCTs involving a total of 520 patients showed that anti-tumour necrosis factor (TNF) therapy significantly delayed radiographic progression compared to placebo (p<0.001 for adalimumab and p=0.0001 for etanercept).18,19 Evidence level 1+

B All patients suspected as having psoriatic arthritis should be assessed by a rheumatologist so that an early diagnosis can be made and joint damage can be reduced.

[Good practice point] Annual reassessment for symptoms of arthritis in patients with psoriasis should be considered.

The lack of agreed diagnostic criteria for PsA has hindered the development of instruments for early detection of the disease. The ClASsification criteria for Psoriatic ARthritis (CASPAR criteria) for the classification of PsA amongst patients with inflammatory joint disease have been validated (see Annex 4).20 Evidence level 2++

B Patients with inflammatory joint disease should be classified as having psoriatic arthritis based on CASPAR criteria.

There is now a recognised association of comorbidities with psoriasis and PsA (see section 4.2). Early recognition of these comorbidities with subsequent implementation of strategies that modify lifestyle and in particular cardiovascular risk factors may affect long term outcomes.21, 22 Evidence level 4


PsA is frequently undiagnosed. A recent European study of 1,511 patients with plaque type psoriasis attending a dermatologist found that 20.6% (95% CI 18.6 to 22.7%) had PsA. Only 3% of patients had had the diagnosis of PsA established before the study.2 Evidence level 3

D Healthcare professionals who treat patients with psoriasis should be aware of the association between psoriasis and psoriatic arthritis.

The introduction of a short, patient-administered questionnaire may raise awareness of and assist in the early detection of PsA. Three questionnaire based screening tools have been developed that may assist in the diagnosis of PsA in patients with psoriasis.

The Psoriasis Epidemiology Screening Tool (PEST) was evaluated in a population of 114 English patients with psoriasis in primary care and rheumatology secondary care, 33 of whom had a validated diagnosis of PsA (see Annex 5). This 5-item questionnaire had a sensitivity of 92%, specificity of 78% and a positive likelihood ratio of 4.1.23 PEST requires validation in dermatology clinics. Evidence level 2+

The Psoriatic Arthritis Screening and Evaluation Tool (PASE) was evaluated in a population of 69 American patients with psoriasis attending a combined dermatology-rheumatology clinic, 17 of whom had a validated diagnosis of PsA. This 15-item questionnaire (seven items relating to diagnosis and eight relating to disease severity) had a sensitivity of 82%, specificity of 73% and a positive likelihood ratio of 3.0.24 Evidence level 2++

The Toronto Psoriatic Arthritis Screen (ToPAS) is a questionnaire based screening tool developed to assist in the diagnosis of PsA in individuals who may or may not have psoriasis. In a population of 688 Canadian patients attending a PsA clinic (134), a psoriasis clinic (123), general dermatology clinic (118), general rheumatology clinic (135) or family medicine clinic (178), 169 of whom had a validated diagnosis of PsA, this 14-item questionnaire had an overall sensitivity of 86%, specificity of 93% and a positive likelihood ratio of 12.6. This instrument was designed to detect PsA in any population rather than in those already known to have psoriasis and as such many of the items relate to the diagnosis of psoriasis rather than arthritis.25 Evidence level 2++

C The use of patient-administered screening questionnaires such as PEST should be considered for early detection of psoriatic arthritis in primary care and dermatology clinics.

No studies concerning laboratory or radiological screening investigations that would be useful in these settings were identified. Two studies involving a total of 484 patients with psoriasis or PsA examined anticyclic citrullinated peptide antibodies for detection of PsA but found the investigation to lack sensitivity.26, 27 Evidence level 2++

B The measurement of serum anticyclic citrullinated peptide antibodies in patients with psoriasis should not be used to screen for psoriatic arthritis.


Patients with psoriasis or PsA have been identified as being at increased risk of a number of comorbid conditions including diabetes mellitus (DM), hypertension (HTN), coronary heart disease (CHD), inflammatory bowel disease (IBD), lymphoma and depression.28-31 Evidence level 2+,3

High body mass index (BMI), smoking and alcohol may influence the onset of disease and, in the case of obesity, its extent.32-37 In addition, smoking, excessive alcohol consumption and obesity may have an adverse effect on comorbid conditions such as cardiovascular disease and diabetes. Evidence level 2+,3

Any discussion of comorbidities must be handled sensitively by healthcare professionals (HCPs) to avoid further stigmatisation of patients with psoriasis. The potential benefits of informing patients must be weighed against the potential to cause anxiety.

The increased risk of developing these conditions may not pertain to all patients with psoriasis as most studies have identified the greatest excess risk in those with the most severe disease. The following lifestyle advice and therapeutic interventions are, therefore, important in those with severe disease but also represent sensible advice for those with mild disease where the link is not as well established.

D Healthcare professionals should be aware of the need to consider comorbid conditions in patients with psoriasis and psoriatic arthritis. Where necessary, detailed assessment should be carried out to accurately identify and manage comorbid conditions.

[Good practice point] Healthcare professionals should take comorbidities into consideration when selecting treatments.


In a population based study assessing the prevalence of cardiovascular risk factors, patients with psoriasis had higher odds of DM, HTN, hyperlipidaemia, obesity and smoking than controls.31 Evidence level 2++

Psoriasis may be an independent risk factor for myocardial infarction (MI) with the greatest relative risk (RR) for young patients with severe disease.29 A study analysing the cumulative incidence of risk factors for MI over time showed that hazard ratios were increased for incident DM, HTN, obesity and hyperlipidaemia in patients with psoriasis compared to the general population.30 It was not possible to establish whether or not these associations related to psoriasis in itself or its treatment. Evidence level 2++

D Evaluation of patients with severe psoriasis or psoriatic arthritis should include annual BMI, DM screening, blood pressure measurement, and lipid profile.

D Consider advising patients with severe psoriasis or psoriatic arthritis that they may be at increased risk of cardiovascular disease and diabetes.


Several studies have shown an association between severity of psoriasis and obesity. It remains unclear whether or not obesity is a cause or effect of psoriasis.38 Evidence level 4


Patients with psoriasis have an increased risk of metabolic syndrome and its individual components. The increased frequency of smoking, OR 2.96 (95% CI 2.27 to 3.84), and alcohol consumption, OR 3.61 (95% CI 1.85 to 7.07), observed in patients with psoriasis does not seem to account for the increased risk.39 Evidence level 3


An increased prevalence of smoking has been noted in UK cohorts of patients with psoriasis.31, 40 An American study, Nurses’ Health Study II, identified current and past smoking as a risk factor for the development of psoriasis in women.36 Evidence level 3


Most studies show an association between alcohol consumption and psoriasis but do not demonstrate causality.41 Heavy alcohol consumption may affect severity of disease, choice of treatment and response to treatment.34,35,37 Evidence level 3

D All patients with psoriasis or psoriatic arthritis should be encouraged to adopt a healthy lifestyle, including:


Psoriasis and PsA affect all aspects of QoL with potentially profound psychosocial implications.42 The impact of psoriasis on mental and physical well-being is comparable to that of other chronic conditions such as cancer and diabetes.4 Psychosocial comorbidities experienced by patients are not always proportional to or predicted by disease severity.10,43 Long term psychological distress can lead to depression and anxiety.

A systematic review of psychiatric morbidity in psoriasis found that psoriasis can have an adverse effect on self image, self esteem and emotional stability. Aspects of QoL affected by psoriasis include physical, psychological, sexual, social and occupational well-being.42 Depressive symptomatology is more common in people with psoriasis than in controls.22 Patients report mental health concerns such as anxiety and depression and a wide range of emotional reactions such as shame, embarrassment, anger and helplessness.44,45 The most difficult aspect is the visibility of psoriasis.46,47 Evidence level 2+,3

NICE has produced guidance on screening for depression that recommends asking two questions:

During the last month, have you often been bothered by:

A ‘yes’ to either question should result in further assessment or referral. NICE recommends asking three further questions to improve the accuracy of assessment in people with chronic physical health problems:

During the last month, have you often been bothered by:

The 9-item Patient Health Questionnaire (PHQ-9) for diagnosis of depression has been validated in UK primary care with a sensitivity of 91.7% (95% CI 77.5 to 98.3%) and specificity of 78.3% (95% CI 65.8 to 87.9%) using a cut off of ≥10. In the same study, the 34-item Clinical Outcomes in Routine Evaluation - Outcome Measure (CORE-OM) was validated with a sensitivity of 91.7% (95% CI 77.5 to 98.2%) and specificity of 76.7% (95% CI 64.0 to 86.6%) with cut off of ≥13. Both instruments are freely available. The CORE-OM takes longer to complete, but measures a broader range of common mental health problems (including depression) as well as functional ability and risk.49 Evidence level 3

The Hospital Anxiety and Depression Scale (HADS) is commonly used in primary care and has been tested in the measurement of psychosocial disability in psoriasis.50 Evidence level 3

Many studies highlight the need for psychosocial support for patients with psoriasis.43-45, 47, 51-55 Psychosocial support is often lacking.56 Evidence level 3

D Assessment of patients with psoriasis or psoriatic arthritis should include psychosocial measures, with referral to mental health services as appropriate.

There is a lack of good quality evidence on whether stress is associated with risk of psoriasis flare or reduced efficacy of treatment. One study of the effects of psychological distress on time to clearance in psoriasis patients treated with psoralen ultraviolet A phototherapy (PUVA) (n=112) found that the group with pathological levels of worrying, defined as Penn State Worry Questionnaire (PSWQ) >60, achieved clearance 1.8 times slower than the low level worriers.57 A study of the effect of daily stressors (measured with the Everyday Problem Checklist) on patients with psoriasis (n=76) found a significant correlation between self reported daily stressors and an increase in itch and Psoriasis Area and Severity Index (PASI) four weeks later.58 The implications for clinical management are unclear. Evidence level 3

No good quality studies on the effectiveness of psychological therapies, stress management or peer support groups in psoriasis or PsA were identified.


A prospective cohort study of patients with PsA found that the incidence of malignancy (all cancers) was not different from that in the general population.59 In a UK retrospective cohort study comparing patients with a history of psoriasis and those without psoriasis, the overall rate of internal malignancy was not increased.60 Two reviews identified an increased RR of cancers of the liver, colon, oesophagus, oral cavity, larynx, lung, bladder, breast and non-melanoma skin cancer in patients with psoriasis.22,38 An increased risk of squamous cell carcinoma (SCC) of the skin in psoriasis patients treated with PUVA has been demonstrated.61,62 Smoking, alcohol consumption and treatments such as immunosuppressive drugs may be important confounding factors. Evidence level 3,4

A UK cohort study comparing patients with (n=153,197) and without (n=765,950) psoriasis identified an association between psoriasis and increased risk of lymphoma. The association was strongest for cutaneous T-cell lymphoma and Hodgkin’s lymphoma.63 Lymphoma is a rare disease, the magnitude of the association is modest, and the absolute risk attributable to psoriasis is low. Several other studies do not support an association between psoriasis and lymphoma.61,64,65 Evidence level 2++,3


Crohn’s disease is found more often in patients with psoriasis than in controls.66,67

In a case control study using an Israeli healthcare provider database, the adjusted OR of chronic obstructive pulmonary disease after controlling for confounders including smoking and obesity was 1.27 (95% CI 1.13 to 1.42).68

A systematic review found that the mean prevalence of uveitis in 10 studies of patients with PsA (n=1,341) was 25.1%.69 Evidence level 2++



In the past, assessments of psoriasis severity have depended on the ability of the observer to rate the visible signs of the disease including the extent of disease together with an assessment of the erythema, thickness and scaling and some subjective account of the effect psoriasis has on the individual. A number of tools have been introduced to assess both the clinical severity of psoriasis and to assess the impact of psoriasis on the patient’s QoL. These have been mainly used in the context of clinical trials but have also been increasingly used within the clinic.

The clinical assessment tools include the PASI, Body Surface Area (BSA), Dermatology Index of Disease Severity (DIDS), and the Physician’s Global Assessment (PGA). The measures most commonly used in clinical practice to monitor disease activity in the skin (eg PASI, PGA, Salford Psoriasis Index) have not been validated as a measure of clinical response in routine practice. The PASI is the most widely used clinical assessment instrument in the UK.70

The patient assessment methods are mainly QoL questionnaires developed using generic, dermatological or disease-specific tools. The main tools used in studies include the generic SF-36® Health Survey, Dermatology Life Quality Index (DLQI) and the Psoriasis Disability Index (PDI).7 Other scoring tools include the EuroQoL score, the Psoriasis Symptom Assessment score (PSA) and the Dermatology Quality of Life Scale (DQOLS). In the UK, the DLQI is the assessment method most used in clinical practice. It is a simple, reliable test that is sensitive to changes in quality of life following treatment.71,72 It can be used without specific training and is well suited to use in primary care.

Introduced mainly in the context of clinical trials of biologic agents, the DLQI (see Annex 2) and the PASI (see Annex 3) are the most used instruments. As they measure different aspects of the severity of the disease, PASI and DLQI do not directly correlate with each other in an individual.

NICE guidance for eligibility for biologic therapy in psoriasis is dependent on fulfilling disease severity criteria based on PASI and DLQI.73-75 Evidence level 4

D Healthcare professionals should be aware that the PASI and DLQI are part of the eligibility criteria for biologic therapy in psoriasis and must be used to assess the efficacy of these agents over time.

D The DLQI should be measured as part of the global assessment of patients with psoriasis.

[Good practice point] In secondary care, the PASI and DLQI should be taken at baseline and then measured serially to aid assessment of efficacy of systemic and biologic interventions.

[Good practice point] Healthcare professionals should have training in the use of the assessment tools.


PsA is a heterogeneous disorder affecting peripheral and axial joints as well as having other features such as dactylitis and enthesitis. The commonly used tools to assess peripheral joint disease are the American College of Rheumatology (ACR) joint count and the Ritchie Index. Measures of clinical response in PsA include the PsA Response Criteria (PsARC); the ACR 20, 50 and 70 improvement response; and the European League Against Rheumatism response criteria (EULAR).76,77 PsARC was specifically designed for PsA (see Annex 6). Improvement is recorded in at least two of four criteria: 20% or greater improvement in physician global assessment of disease, 20% or greater improvement in patient assessment of disease activity, 30% or greater improvement in tender joint count and 30% or greater improvement in swollen joint count. Improvement in either tender or swollen joint score is mandatory and there should be no worsening of any component. The PsARC discriminates well between effective treatment and placebo but focuses only on peripheral manifestations.77

Measures of function and disability include the Health Assessment Questionnaire (HAQ), SF-36 and the Psoriatic Arthropathy Quality of Life Index (PsAQoL). Of the QoL measures only PsAQoL has been validated in PsA.78

Assessment tools used in ankylosing spondylitis (AS) can be used in the assessment of patients with psoriatic spondyloarthropathy. The BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) consists of 10 cm visual analogue scales used to answer questions pertaining to the five major symptoms of AS: fatigue, spinal pain, joint pain and swelling, areas of localised tenderness and morning stiffness (see Annex 7).79 The BASFI (Bath Ankylosing Spondylitis Functional Index) measures functional abilities in 10 activities of daily living on a 10 cm visual analogue scale (see Annex 8).80

Adequate response to biologic treatments in PsA has been defined as an improvement in at least two of the four PsARC criteria, one of which has to be joint tenderness or swelling score, with no worsening in any of the four criteria.81 Adequate response to biologic treatments has been defined in AS as:

D PsARC should be used to monitor response to biologic agents in patients with peripheral psoriatic arthritis.

D BASDAI and spinal pain visual analogue score should be used to monitor response to biologic agents in patients with axial disease.

Patients with both peripheral and axial disease should be assessed for biologic treatment eligibility and response using both PsARC and BSR ankylosing spondylitis guidance. Some patients may not respond to treatment for peripheral disease but respond for axial disease, and vice versa.

section 5>

Guideline Index Page | SIGN Methodology | Summary of Recommendations

Scottish Intercollegiate Guidelines Network, Healthcare Improvement Scotland, Gyle Square, 1 South Gyle Crescent, Edinburgh EH12 9EB
Tel. 0131 623 4720 Web contact
Last modified 27/08/15 © SIGN 2001-2013

Psoriasis and psoriatic arthritis in adults <Guidelines <Home