Psoriasis is a common, chronic, inflammatory papulosquamous disorder typically characterised by well-demarcated, scaly plaques and a relapsing-remitting course.
Psoriasis is a common skin disorder that affects an estimated 1-3% of the world's population. There are a number of distinct clinical patterns, the most common being chronic plaque psoriasis which accounts for 80-90% of cases.
It is frequently associated with systemic diseases (e.g. psoriatic arthritis) and can also impact individuals' self-esteem and mental wellbeing. Treatment tends to be with topical therapies (e.g. emollients, steroids, vitamin D analogues) with phototherapy and systemic therapies reserved for more severe or treatment-resistant disease.
It is estimated that 1.3-2.2% of people in the UK are affected by psoriasis.
This is similar to worldwide estimates of 1-3%. It can occur at any age, but there are two peaks between the ages of 20-30 and 50-60 (varies between studies).
Psoriasis is more common in white people when compared to other ethnicities. Overall there is an equal gender balance.
Figures from NICE CKS.
There are a number of factors that may trigger or exacerbate disease.
Other risk factors include:
Psoriasis is an immune-mediated disease featuring hyperproliferation of the epidermis.
The pathophysiology of psoriasis is complex and incompletely understood. It has been demonstrated that the immune system plays a key role - becoming activated and resulting in inflammatory plaques on the skin.
It is thought that antigenic stimuli initiate an immune response from elements of the innate immune system in the skin of susceptible individuals. This results in the release of inflammatory mediators (e.g. interferon-alpha). Myeloid dendritic cells are attracted and activated producing interleukin-23 triggering the involvement of T cells. Further cytokine production (including interleukin-17A) amongst other factors stimulate hyperproliferation of keratinocytes.
It is estimated that a third of patients with psoriasis will develop psoriatic arthritis.
Psoriatic arthritis is a chronic seronegative inflammatory arthritis. It is estimated that around a third of people with psoriasis will develop psoriatic arthritis (though figures vary). The onset of arthritis normally follows that of skin disease by 5-10 years though occasionally this temporal relationship is reversed.
Psoriatic nail disease affects 90% of patients with a combination of psoriasis and psoriatic arthritis.
There are a number of other conditions that are associated with psoriasis. Patients are more likely to have inflammatory bowel disease (in particular Crohn’s disease), metabolic syndrome, cardiovascular disease and other autoimmune disorders.
Several ocular pathologies appear to occur with greater frequency including uveitis, blepharitis and conjunctivitis.
Psoriasis is a complex skin condition with a number of clinical subtypes, the most common being chronic plaque psoriasis which accounts for 80-90% of cases.
Chronic plaque psoriasis is the most common subtype and is characterised by raised, scaly, well-demarcated plaques. It is typically symmetrically distributed and often affects the scalp, extensor surfaces, trunk, gluteal cleft and knees. Lesions are typically itchy and may become fissured and painful over joint lines, on the palms of the hand or soles of the feet.
The appearance of psoriasis may differ depending on skin colour. In fair-skinned populations, plaques are typically described as erythematous and pink or red with a silver-white scale. In Hispanics the plaques may be salmon coloured with a silver-white scale. On black skin, psoriasis may have a somewhat violet appearance with a scale that appears more greyish. On more pigmented skin post-inflammatory hyperpigmentation may occur.
Nail changes can be seen in patients with all subtypes of psoriasis. Fingernails are involved in around 50% of cases and toenails in 35%. In patients with psoriatic arthritis, nail changes are very common affecting 90%.
Typical changes include:
Also termed flexural psoriasis, inverse psoriasis follows a different pattern of distribution to chronic plaque psoriasis. It affects ‘Intertriginous’ areas - points where skin touches/rubs together. Areas affected include the axilla, groin and genital area, inframammary folds and gluteal cleft.
Also termed raindrop psoriasis, it presents as a sudden eruption of small circular plaques classically 2 weeks following a streptococcal sore throat. It can also occur as a flare of disease in patients with pre-existing psoriasis.
It is generally self-limiting resolving over 3-4 weeks but around a third will develop classic plaque psoriasis.
Erythrodermic psoriasis is a rare subtype accounting for around 1-2.5% of cases. It refers to a severe form of the disease characterised by widespread erythema and psoriasis affecting a large portion of the bodies surface area (at least 75-90%). It often occurs on the background of known psoriasis but may represent the first presentation.
Triggers include recent illness (particularly infectious), medications (e.g. steroids) and emotional stress. It presents with a range of severity but can be life-threatening. Patients require hospitalisation (in most cases), supportive care and specialist management. Immunosuppressive agents and biologics (e.g. infliximab) are used in its treatment.
Generalised pustular psoriasis (GPP) can be subdivided into acute GPP and generalised annular pustular psoriasis. Acute GPP is characterised by rapidly developing and widespread erythema and pustules. The pustules may coalesce forming ‘lakes of pus’. They tend to resolve over days leaving the erythema and scaring. It can represent a dermatological emergency and patients are often systemically unwell with fever, malaise and arthralgia.
Generalised annular pustular psoriasis follows a subacute, recurring course. Patients develop plaques with peripheral pustules.
Localised (palmoplantar) psoriasis generally affects the hand and feet. Pustules develop along with plaques. It is strongly associated with smoking.
The management of chronic plaque psoriasis may involve topical agents, phototherapy and systemic therapies.
Psoriasis is (in most cases) a chronic condition and though no cure exists, treatments can be effective at reducing and even clearing disease. It can be expected to recur, particularly after the cessation of treatment.
There are a number of sub-types of psoriasis each with its own treatment pathway. Here we will focus on the most common form, chronic plaques psoriasis.
Topical agents are typically offered first line. Phototherapy and systemic therapies are generally used second or third line but maybe initiated earlier in those with severe/extensive disease or where topical agents are ineffective (e.g. nail disease).
Topical therapies help to reduce both symptoms (itch) and reduce/clear plaques. Active agents such as topical steroids and vitamin D analogues are added to regular emollient use.
The choice of agent should take into account patient factors, preferences, side effect profiles and the practicality of the various regimens. Options include:
Phototherapy is used as second or third-line therapy in patients with disease that does not respond adequately to first-line topical measures. Care is guided by dermatologists following a referral from primary care. There are two main forms of phototherapy used to treat psoriasis:
Systemic therapies efficacy has to be weighed against their potentially severe side effects. As such their use is controlled by dermatologists. In those requiring systemic treatment the options include:
Psoriasis is associated with an increased risk of psychosocial difficulties.
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