Psoriasis

Definition/diagnostic criteria Psoriasis is a chronic, inflammatory skin condition characterised by a relapsing and remitting course. The most common type, plaque psoriasis, features well-defined red, scaly plaques. Other forms include guttate psoriasis, pustular psoriasis, nail psoriasis and psoriatic arthritis.

The condition involves a malfunction of the immune system, particularly the T-cells, and is often genetically linked. Psoriasis is triggered by various factors, including skin injuries (Köebner phenomenon), stress, smoking, alcohol, certain medications (e.g. lithium, anti-malarials), and infections (e.g. streptococcus).

Epidemiology Psoriasis affects around 1.3% to 2.2% of the UK population and can develop at any age, including in children (0.71%), with most cases occurring before the age of 35. There is a significant association between psoriasis and joint disease (up to 30%). Nail changes are present in about half of the individuals affected, with a higher incidence in those with psoriatic arthritis.

Diagnosis The diagnosis of psoriasis is clinical based on the appearance according to type:

Plaque psoriasis: Characterised by raised, red patches covered with a silvery white buildup of dead skin cells or scale. These patches are often found on the scalp, elbows, knees, and lower back. Psoriasis can manifest differently on black and ethnic minority skin types, often appearing as darker patches with less scaling.

Guttate psoriasis: Often starts in childhood or young adulthood. It appears as small, dot-like lesions, often triggered by a strep infection.

Flexural psoriasis: Shows up as very red lesions in body folds, such as behind the knee, under the arm, or in the groin. It may appear smooth and shiny.

Pustular psoriasis: Primarily seen in adults, characterised by white blisters surrounded by red skin. It can be localised to certain areas of the body, like the hands and feet, or cover most of the body.

Erythrodermic psoriasis: An inflammatory form that often affects most of the body surface. It is marked by a fiery redness of the skin. This can be life-threatening and requires urgent referral to secondary care.

Nail psoriasis: Signs include discolouration, pitting of the nails, and separation of the nail from the nail bed.

Investigations An HIV test is recommended in new onset of severe psoriasis, unusual or atypical presentations or if there is a lack of expected response to treatment.

Treatment

General

• Lifestyle advice such as weight loss, smoking cessation, and alcohol reduction (if appropriate).
• Identify and refer patients with psoriatic arthritis to reduce the long-term complications of joint destruction
• Target modifiable risk factors for cardiovascular disease, particularly in cases of severe psoriasis and in patients with psoriatic arthritis

Skin

Treatments include emollients, steroid creams or ointments, vitamin D analogues, calcineurin inhibitors, coal tar, and dithranol. Treatments are recommended according to the type of psoriasis and site.

Emollients make the skin more comfortable and reduce the amount of scale for all types of psoriasis.

The Primary Care Dermatology Society recommend calcipotriol and betamethasone (potent steroid) combination products first-line to encourage a rapid improvement and hence adherence in chronic plaque psoriasis.

Descaling agents may be required for patients with very thick scale or with scalp psoriasis (e.g diprosalic ointment, sebco or cocois).

Products containing potent steroids are best avoided on areas of thin skin e. g the face, flexures, and the genitalia.

Secondary care treatments include phototherapy, non-biological medications (e.g. methotrexate) and biological treatments targeting the immune system.

Prognosis The prognosis of psoriasis varies. While it’s a chronic condition with no cure, it can be managed effectively with treatment. Psoriasis significantly impacts the quality of life, making psychological support and patient education crucial aspects of management.