In severe and long-standing cases, skin covered by clothing (e.g. buttocks) may also be affected and because of this the role of sunlight may not be so obvious. In addition the condition often persists throughout the year, although usually much worse in the summer months.
Actinic prurigo is sometimes called ‘Hutchinson prurigo’.
What causes actinic prurigo?
Actinic prurigo occurs when affected individuals are exposed to long- and short-wave ultraviolet radiation (UVA and UVB). The reason why this reaction between skin and sunlight occurs is still unknown. Current research suggests that actinic prurigo may be an immunologically-mediated genetic disease as a family history of the condition has been found in some patients. Genetic studies have shown there to be an increased frequency of Human Leukocyte Antigen (HLA) DRB1*0407 in affected individuals.
Who gets actinic prurigo?
Actinic prurigo may affect people of all skin types but more commonly occurs in people of Latin American and American Indian descent with darker skin types. Hence it is common in Mexico and Central and South America. It rarely affects people in Europe and Asia.
It can affect people of all ages. Oe third of patients are children, in many cases it first occurs in childhood before puberty. When the condition appears during childhood both males and females are equally affected. However, in adult-onset actinic prurigo, women are two times more frequently affected than men.
What are the clinical features of actinic prurigo?
Actinic prurigo is characterised by an intensely itchy rash. The rash consists of an eruption of small, red and inflamed bumps (papules), thickened patches (plaques) and (lumps) nodules that are frequently scratched. The rash usually appears hours or days following sun exposure. Chronic scratching, ulcers, weeping, crusting and scaling are found in 60-70% of patients. It may look very like atopic dermatitis (eczema), but is more severe on sun-exposed sites. Areas affected include:
- Sun-exposed areas of the face such as the cheeks, nose, forehead, chin and earlobes. V of the neck and chest, upper sides of the arms and hands.
- Lips are involved in 60-70% of cases (in 10% the lips are the only site affected).
- Conjunctiva of the eye is affected in 45% of patients.
The condition usually starts or worsens in spring and summer. In many patients symptoms persist throughout the year, particularly in tropical areas.
What is the treatment for actinic prurigo?
There is no cure for actinic prurigo. The main goal is prevention by avoiding sun exposure. Patients must realise their condition will worsen during the sunniest months of the year and they must adhere to sun protection strategies to avoid or reduce outbreaks.
Some medications have been used to help relieve the symptoms of actinic prurigo. These include:
- Emollients to relieve itching.
- Topical corticosteroids.
- Antimalarials such as hydroxychloroquine for their anti-inflammatory action.
- Thalidomide – once improvement occurs the drug should be gradually reduced, then stopped. It can be started again in cases of relapse. Because thalidomide may cause birth deformities, it must be used cautiously, particularly in women of childbearing years.
In some cases the condition spontaneously resolves in early adult life. However, in others it remains throughout their lifetime with relapses and outbreaks according to the seasons.