Abnormal light sensitivity ("photosensitivity") is a major feature of most forms of lupus, including both systemic lupus erythematosus (SLE) and lupus that is mainly limited to the skin (cutaneous lupus) such as "discoid" lupus (DLE) and "subacute lupus" (SCLE). We shall discuss DLE and SCLE in detail below.
How common is photosensitivity in lupus?
Photosensitivity, defined by the American College of Rheumatology as "a skin rash as a result of unusual reaction to sunlight, by patient history or physician observation" has been reported in 57-73% of patients with SLE. In patients with cutaneous lupus, photosensitivity affects 50% of patients with DLE and 70-90% of those with SCLE.
What does photosensitivity mean for lupus patients?
Lupus patients are particularly susceptible to sunburn which may lead to "prolonged erythema" (redness). Sunlight may also cause the development of new lupus skin lesions (e.g. DLE and SCLE). Sunlight can also lead to flares of disease activity in SLE, including joint pains and fatigue. Finally, sunlight causes other skin diseases such as polymorphic light eruption (PLE or "prickly heat") which is usually fairly mild but very irritating and has recently demonstrated in 50% of lupus patients, compared with 15% of the general population. Part of my current research involves talking to families of lupus patients to find out whether PLE is also commoner in the family members. We have recently demonstrated with a large twin study that susceptibility to PLE is determined by multiple genes. We are, therefore, examining whether PLE and lupus share common genes that may cause both skin diseases.
Why are lupus patients sensitive to sunlight?
The science of sunlight in lupus is complex and poorly understood. Several studies over the last 30 years have examined the role of ultraviolet light in lupus. Ultraviolet light (UV) is invisible light from the sun with a shorter wavelength than visible light. Ultraviolet light is divided into UVA, UVB and UVC (which does not reach us because it is absorbed into the atmosphere). In general, UVA ages the skin and the UVB burns (ie A ages, B burns). Early studies from the 1960s suggested that only UVB was important in causing photosensitivity in lupus. However, more recent studies have shown than UVA can also cause skin problems in lupus. The substances in the skin that react with the UV light in lupus are unknown but the suspects include various proteins, as well as genetic material ("DNA" and "RNA").
How does my rash develop after sun exposure?
The current theory, based on experimental evidence, is that UV light causes skin cells to express particular protein molecules ("antigens") on their surface. These antigens, including "Ro" and "La" (named after the first two letters of the patients in which they were discovered) on the surface of the skin cells react with antibodies ("anti-Ro" and "anti-La") which latch onto them. These antibodies then attract white blood cells to the skin which attack the skin cells, leading to the rash. Recently it has been observed that certain skin cells in lupus patients switch themselves off ("apoptosis") more readily than they should. This may be related to the attack from the immune system that we mentioned above. Another recent study found too much nitric oxide may be made in the skin of lupus patients after sun exposure, which may lead to redness and inflammation. It is unknown why any of these mechanisms are more active in patients with lupus.
What do the different lupus rashes look like?
The facial "butterfly rash" of systemic lupus erythematosus usually comes on after sun exposure and is associated with flares of the SLE itself. It usually occurs over the cheeks and nose (but can occur elsewhere) and usually heals without scarring within weeks.
Discoid lupus (DLE) refers to "disk-like" lesions which usually, but not always, occur in sun-exposed sites. These lesions develop slowly and heal over several months, often without scaring.
Subacute lupus (SCLE) is the other major type of specific skin lupus. It is highly photosensitive and usually takes the form of red, circular shapes on the chest, back and arms. It may also be quite scaly and resemble psoriasis. This type of skin lupus is particularly associated with autoantibodies in the blood to the Ro antigen that we mentioned above. SCLE tends to heal over weeks or months and is usually non-scarring.
DLE and SCLE may both occur on their own without SLE. However, SLE can develop in patients who start with DLE and SCLE, but it tends to be much milder illness than typical SLE.
How can I protect myself against ultraviolet light?
Sun-avoidance and appropriate sunscreens may reduce the need for treatment with topical steroids or systemic therapy with tablets.
Dermatologists have suggested sun avoidance in britain from 11am to 3pm, March to september for photosensitive lupus patients. This is easier said than done! using broad-rimmed hats and wearing long sleeves and trousers are all simple and effective methods of photoprotection.
Topical sunscreens form the next major component of photoprotection. Sunscreens are either organic chemicals which absorb UV light or inorganic pigments such as titanium dioxide which absorb and scatter UV light. The sun protection factor (SPF) is proportional to the light sensitivity without sunscreen divided by light sensitivity with sunscreen, but it only applies to UVB protection. There is no universal method of labelling sunscreens for protection against UVA. Use of broad-spectrum sunscreens (covering UVA and UVB) should therefore be used and prescribed if necessary.
A study that was published in February found that we tend to apply less sunscreen than is needed to achieve the manufacturer's recommended SPF.
The most frequently missed areas are the back and sides of the neck, the temples and the ears which also tend to be the areas where photosensitive lupus patients frequently experience problems.
Because car windows and clouds only protect against UVB, not UVA, photoprotection should not be limited just to sunny days in order to minimize UVA exposure. UV-blocking films may be applied to car and house windows.
Sources of UV light other than sunlight can also cause skin problems in lupus. Photosensitivity in lupus has been reported with fluorescent tube lights, which mainly emit UVB, and photocopiers, which emit mainly UVA. Fluorescent tubes may be fitted with acrylic shields which eliminate UVB emission.
Can UV light be used for healing in lupus? This is a controversial subject. One group of doctors from Louisiana have published a series of small studies that suggest that light treatment ("Phototherapy") can be used in some SLE patients to reduce disease activity. The light used is a form of UVA. This treatment is not widely used because, as we mentioned above, UVA can also cause the lesions of lupus skin disease to appear. Furthermore, phototherapy has been documented to bring on antinuclear antibodies (one of the hallmarks of lupus) in the blood of healthy patients! the jury is still out!