Chronic plaque psoriasis is the most common type of psoriasis. Although any part of the body may be affected, the most commonly affected sites are the elbows, knees, and scalp. 'Topical' treatments (i.e. treatments applied to the skin) are usually tried first. These include vitamin D products, topical corticosteroids, tar-based preparations, dithranol, salicylic acid, and vitamin A products. As chronic plaque psoriasis is a long-term condition, it is important to find out which treatments work best and what adverse effects they have. This review describes average benefits of different treatments, while recognising that individuals will vary in their experience of each treatment.
The evidence was based on 177 studies, which, in total, included 34,808 people. Studies were typically about 7 weeks' long, but this ranged from 1 week to 52 weeks. Vitamin D products were found to work better than placebo (the base cream or ointment). Potent topical corticosteroids (strong, e.g. betamethasone dipropionate) and very potent (very strong, e.g. clobetasol propionate) topical corticosteroids were also effective.
Some studies compared vitamin D products directly with potent or very potent corticosteroids. These products had similar effects when applied to the body, but corticosteroids worked better than vitamin D for scalp psoriasis. Treatment that combined vitamin D with a corticosteroid was more effective than vitamin D alone and more effective than the topical corticosteroid alone. Vitamin D products generally performed better than coal tar, but studies found conflicting results when comparing vitamin D with dithranol.
Whether applied to the body or to the scalp, potent corticosteroids were less likely than vitamin D to cause 'local adverse events', such as skin irritation or burning, and people were therefore more likely to stop using vitamin D products. When studies examined whether topical treatments had effects within the body ('systemic adverse events'), we found no difference between placebo and any other treatment. However, this may be because many trials did not properly assess systemic adverse events, rather than because there really was no difference.
More long-term studies would help doctors and people with psoriasis decide on the best way to treat this chronic condition.