Plaque psoriasis (‘psoriasis vulgaris’) accounts for 90% of cases of psoriasis and is characterised by well-demarcated, infiltrated red plaques covered with a coarse silvery scaling (Figure 6a). Patients report itch, pain and bleeding and although the most commonly-affected sites include elbows, knees, scalp, periumbilical and lumbar regions, psoriasis can affect any area of the body including the nails (Nestle et al., 2009; Boehncke & Schön, 2015; National Psoriasis Foundation, 2018).
Nail signs of psoriasis include: pitting, leukonychia, onycholysis, subungual hyperkeratosis, transverse ridging, nail plate crumbling, splinter haemorrhages, and increased nail thickness (Pasch, 2016; Ngan & Oakley 2016). The specific pathogenesis of nail psoriasis is not known, however there is a clear link with psoriatic arthritis; 80% of patients with nail symptoms will have psoriatic arthritis, compared with 50% with cutaneous symptoms alone (Williamson et al., 2004). Nail psoriasis can be unsightly, may cause pain and functional disability, and is vulnerable to secondary infection. Topical treatments require long-term application, improvement may only become apparent after three months, and often a year of treatment is necessary to see the extent of response to a topical therapy (Pasch, 2016).
Other manifestations can include skin affected only in the axillae or groin (‘inverse psoriasis’), or an acute exanthematic form with multiple keratotic papules (‘guttate psoriasis’, see Figure 6b). Guttate psoriasis is the most common type in children and young people below the age of 30, and may develop suddenly following a streptococcal throat infection or influenza (Boehncke & Boehncke, 2014; National Psoriasis Foundation, 2018). Meanwhile, erythrodermic psoriasis is a rare form that is particularly inflammatory and frequently affects most of a person’s body surface. It generally appears on patients with unstable plaque psoriasis affecting about 3 percent of people with psoriasis during their lifetime. It is characterised by widespread lesions that are not clearly defined and by shedding of large “sheets” of skin over a large area of the body. People with erythrodermic psoriasis frequently experience severe illness associated with it, such as congestive heart failure, and may require hospitalisation (National Psoriasis Foundation, 2018).
Pustular psoriasis is a group of conditions which, as the name suggests, are characterised by the presence of white pustules surrounded by red skin. It typically affects adults and can be localised or more generalised across the body. The pustules are not a sign of infection, but are neutrophil filled and non-infectious (National Psoriasis Foundation, 2018; Twelves et al., 2018).
Psoriasis exclusively involving the palms and soles is known as palmoplantar psoriasis and can present as hyperkeratotic plaques or as pustules (Handa et al., 2010).