The diagnosis of psoriasis in adults is primarily based on clinical findings NICE CKS. When assessing a person with suspected psoriasis, it is important to evaluate the disease severity, the impact on physical, psychological, and social wellbeing, and to screen for psoriatic arthritis and other comorbidities NICE CG153.
Key aspects of assessment include recording the results of a static Physician's Global Assessment (classified as clear, nearly clear, mild, moderate, severe, or very severe), the patient's own assessment of severity, and the body surface area affected NICE CG153. It is also crucial to note any involvement of high-impact and difficult-to-treat sites such as the face, scalp, palms, soles, flexures, and genitals, as well as any nail involvement NICE CG153. Systemic upset, such as fever and malaise, can be present in unstable forms like erythroderma or generalised pustular psoriasis NICE CG153. In specialist settings, the Psoriasis Area and Severity Index (PASI) is used to assess severity NICE CG153. Adults with any type of psoriasis should be offered annual assessment for psoriatic arthritis, particularly within the first 10 years of psoriasis onset, using validated tools like the Psoriasis Epidemiological Screening Tool (PEST) NICE CG153 Helliwell & Taylor 2005.
Psoriasis is not an infectious condition NICE CKS.
Differentiating psoriasis from other skin conditions is usually achieved through clinical assessment NICE CKS. However, in rare cases, a skin biopsy may be necessary to distinguish psoriasis from other inflammatory skin conditions NICE CKS Johnson & Armstrong 2013. Diagnostic uncertainty is a key reason for referral to a specialist dermatology service NICE CKS,NICE CG153. Furthermore, suspected generalised pustular psoriasis or erythrodermic psoriasis are medical emergencies requiring immediate same-day specialist dermatology assessment and ongoing management NICE CKS,NICE CG153. Referral to a rheumatologist is indicated if psoriatic arthritis is suspected, as early diagnosis can reduce the risk of erosive joint damage NICE CKS. Severe or atypical psoriasis is also considered an HIV indicator condition NICE CG153.
Key References
- CKS - Psoriasis
- CG153 - Psoriasis: assessment and management
- NG65 - Spondyloarthritis in over 16s: diagnosis and management
- (Helliwell and Taylor, 2005): Classification and diagnostic criteria for psoriatic arthritis.
- (Johnson and Armstrong, 2013): Clinical and histologic diagnostic guidelines for psoriasis: a critical review.
- (Young et al., 2017): Psoriasis for the primary care practitioner.