Chronic actinic dermatitis (CAD)
Also known as photosensitivity dermatitis and actinic reticuloid (PD/AR) syndrome; persistent
light reaction
What is it?
CAD is a rare chronic inflammatory skin condition triggered by abnormal sensitivity to sunlight.
What causes it?
Ultraviolet (UV) radiation causes an inflammatory reaction in the skin; specifically, UVB, UVA and rarely, visible wavelengths of light. The reaction is similar to that seen in allergic contact dermatitis, and it is thought that an antigen in the skin is sensitised by light to stimulate an allergic reaction by the body’s immune system.
Who gets it?
It typically occurs in men over 50 years of age, particularly those who spend a lot of time outdoors. It is more common in temperate countries and its appearance worsens in summer or after sun exposure. All races may be affected, and it is not genetically inherited. People with CAD may have other types of inflammatory skin conditions such as atopic dermatitis, seborrhoiec dermatitis and allergic contact dermatitis. There may also be an association with HIV infection.
What does it look like?
Affected skin resembles chronic eczema; it is severely itchy, red, dry and thickened. Skin creases are prominent. The rash appears predominantly on sun exposed areas (face, neck, V-shaped area on chest, back of hands and forearms). It is worsened by exposure to sunlight, although some people can react to artificial light such as fluorescent lamps.
How is it diagnosed?
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- CAD is suspected by its appearance and location on sun exposed areas. Tests the dermatologist may perform include:
- Phototests, or light tests, whereby UVB, UVA and/or visible light is directed onto exposed skin to trigger am eczema like skin reaction, supporting the diagnosis of CAD
- Blood, urine and stool tests to exclude autoimmune and other light-sensitive disorders
- Patch testing to identify chemical triggers and exclude allergic contact dermatitis, such as to drugs or plant substances
- Biopsy of the skin may help distinguish CAD from other inflammatory skin diseases
How is it treated?
The treatment approach depends on the severity of the disease. Importantly, avoidance to sun exposure is advised for all affected individuals, especially during peak UV times. Sun protection should include wearing clothing to cover bare skin and applying broad spectrum, high-protection sunscreen. If a contact allergy is implicated, it is necessary to cease exposure to the substance.
Skin based therapy includes:
- A strong steroid cream or ointment
- Tacrolimus or pimecrolimus cream
- Moisturiser for dry skin
- Fragrance-free soap to clean skin
Desensitisation with controlled exposure to UV radiation may be attempted under dermatologist supervision.
What is the outcome?
One study reported that the disease resolves in 10% of people after 5 years, 20% after 10 years and 50% after 15 years. Although it may spontaneously resolve, more commonly it is a chronic condition that persists for life. The symptoms can be controlled with careful sun avoidance and sun protection.
Sources:
Rooks Textbook of Dermatology, Chronic Actinic Dermatitis
British Association of Dermatologists
Dermatology Advisor
This information was written by Dr Alvin Lim, Dr Davin Lim
