Psoriasis

Psoriasis is an autoimmune disease, characterised by symptoms associated with inflammation in the skin and joints. Autoreactive T cells are involved in the autoimmune process that leads to the manifestation of psoriasis. The condition is linked to comorbidities, including psoriatic arthritis, cardiovascular and vascular inflammation, diabetes mellitus type 2, hypertension and metabolic syndrome (combination of insulin resistance, obesity and dyslipidaemia) (Amin et al, 2020). It is estimated that 1.9% of the UK population has psoriasis (Parisi et al, 2020). Psoriasis affects both male and females equally, and often appears for the first time in teenage years, early adulthood or in people who are around 50 years old (Boehncke et al, 2010). Psoriasis is rarer in children, with a global prevalence of 0.7–1.2%, and is associated with more severe diseases and increased likelihood of obesity and metabolic syndrome (Megna et al, 2015).

Psoriasis can range in severity and type. Chronic plaque psoriasis is the most common form of the condition - present in 85% of psoriasis cases - and is characterised by salmon-pink, well-demarcated, symmetrical plaques with silvery scales on the extensor surfaces, such as the knees, elbows, sacrum and scalp (Burden and Kirby, 2016). Other types of psoriasis include flexural (or inverse) psoriasis - affecting flexural and genital areas - guttate and nail psoriasis. Most people with psoriasis display more than one type of the condition. Pustular and erythrodermic psoriasis are severe rare forms of the condition, which can cause a patient to become systemically unwell. Palmar-plantar pustulosis affects the palms of the hands and soles of the feet, but is no longer classified as psoriasis, as genetic research has shown that it has no association with the PSORS1 gene loci. This condition is associated with smoking and is more common

The aetiology of psoriasis is attributed to a complex immunological process, characterised by complications in T cell function. Th17 cells - a subtype of T-helper cells which produce interleukin 17 - play a significant role in promoting the inflammatory response associated with psoriasis (Boehncke et al, 2010). Increased levels of proinflammatory cytokines, such as tumour necrosis factor-alpha, are seen in patients with psoriasis, causing changes to vascular, immunological and inflammatory functions (Gottlieb et al, 2008). This leads to accelerated proliferation and incomplete differentiation of epidermal cells in the skin.

There are several trigger factors that lead to the manifestation of psoriasis (Table 1), so it is important to identify any of these when assessing a patient. Psoriasis is hereditary; 40% of patients with psoriasis and psoriatic arthritis have a family history of the condition, although the exact genetic loci involved have not yet been identified (Solmaz et al, 2020).

Diagnosis of psoriasis is based on clinical history (including family history) and examination showing signs and symptoms of psoriasis and psoriatic arthritis.

Disease severity should be assessed by completing a PASI score (Psoriasis Area Severity Index), which classifies psoriasis as:

• absent
• mild
• moderate
• severe
• very severe

It is also important to assess nail symptoms, high-impact areas and sites that are difficult to treat (face, scalp, palms, soles, flexures and genitals). The psychosocial impact of psoriasis should be assessed by asking the patient about how their quality of life has been affected, using the Dermatology Life Quality Index tool (National Institute of Health and Care Excellence (NICE), 2017; Scottish Intercollegiate Guidelines Network (SIGN), 2010). Psoriasis can often impact patients’ mental health, as many find it difficult to cope with changes to their body. Elevated levels of pro-inflammatory markers are linked to mental health conditions, and people with psoriasis are 1.5 times

Treatment options depend on the pattern and severity of psoriasis; several treatments may be needed to create a suitable regimen. Education and support on the correct application of topical treatments is key to ensuring treatment efficacy and support for patients. Treatments for psoriasis include emollients, which are topical therapies generally prescribed in primary care. Secondary care treatments include phototherapy, systemic drug therapies and biological agents. The NICE (2017) and SIGN (2010) guidelines recommend topical treatments for care pathways of all psoriasis types on the trunk and limbs, scalp, face, flexures and genitals.