Ultraviolet light treatment
Ultraviolet light treatment uses a particular band of the nonvisible light spectrum to treat psoriasis and a variety of other skin diseases. It can be used alone or in combination with other medications applied directly to the skinor taken internally.
Ultraviolet (UV) light treatment is used primarily in cases of severe psoriasis that have not responded to other medications or in cases affecting large portions of the body. Patients will typically receive a series of 3-5 weekly treatments for a month or more to bring their psoriasis symptoms into check. They may also receive periodic maintenance treatments to prevent recurrence oftheir psoriasis. Other skin conditions treated with UV light treatments arevitiligo, a condition in which people lose pigmentation in large patches of their skin, and atopic dermatitis, an allergy-related skin condition that produces itchy, reddish, and scaly patches of skin.
Exposure to UV radiation is known to prematurely age the skin over time and increase the risk of skin cancer. These potential effects should be weighed against the potential benefits of the treatment. A history will be taken regarding sun exposure and burning, medications, such as diuretics, that may increase UV sensitivity exposure, and any history of skin cancers. Sometimes, UV light treatments are given in combination with photosensitizing agents, which maximize UV's effects on the skin. Patients who receive these agents, called psoralens, must take care to avoid exposure to sunlight, which also contains UV radiation. Exposure to UV radiation can also cause cataracts and other eyedamage, so the patient's eyes must be adequately shielded during the treatments.
UV light treatment can employ one of two bands of the ultraviolet spectrum: ultraviolet A (UVA), and ultraviolet B (UVB). Patients receive full body treatments in special light boxes; smaller areas of the skin are sometimes treatedwith hand-held devices.
Psoriasis is the most common skin disease treated with UVB light treatment. Its mechanism of action remains unclear, but investigators speculate it may kill abnormal skin cells or alter immune system reactions in the skin. Most patients require 18-30 treatments before substantial improvement or complete clearing is seen. The intensity of the UV applied will vary depending on the patient's skin type. Fair-skinned patients will start with a relatively weaker dose; dark-skinned patients, a stronger dose.
The Goeckerman regimen, a treatment that combines UVB light with coal tar applied to the skin, is among the oldest and most frequently used treatments forpatients with moderate to severe psoriasis. The coal tar is a photosensitizing agent, and, when it interacts with UVB, it appears to limit the abnormal turnover of skin cells characteristic of psoriasis.
Another kind of treatment involves psoralens, which are photosensitizing agents found in plants. They have been known since ancient Egypt but have only been available in a chemically synthesized form since the 1970s. Psoralens aretaken systemically or can be applied directly to the skin. The psoralens allow a relatively lower dose of UVA to be used. When they are combined with exposure to UVA in PUVA, they are highly effective at clearing psoriasis.
Choosing the proper dose for PUVA is similar to the procedure followed with UVB. The physician can choose a dose based on the patient's skin type. Often,however, a small area of the patient's skin will be exposed to UVA after ingestion of psoralen. The dose of UVA that produces uniform redness 72 hours later becomes the starting dose for treatment.
Some patients experience nausea and itching after ingesting the psoralen compound. For these patients "bath PUVA" may be a good option.
No major preparation is required for UV light treatments. Areas of the skin that are especially sensitive to the effects of UV light, such as the groin, backside, or face, are shielded during the treatments. Areas not affected by psoriasis are also covered. Special goggles are worn to protect the eyes.
No major aftercare is required following UV light treatments. Patients, however, must take great care to limit or eliminate other exposures to UV radiation, such as from sunlight or tanning beds, because of the increased risk of premature aging of the skin and the development of skin cancers.
People who receive UV light treatments are at higher risk of premature agingof the skin, and of developing skin cancer. These risks should be balanced against the benefits of treatment.
Psoriasis will normally show significant improvement to complete healing withthree to five UVB treatments a week for about four to five weeks. PUVA treatments may require a bit longer to take effect, but because the overall dosageof UV is lower, they are thought by some investigators to be a safer alternative to UVB treatments.
Modern light boxes carefully control the dosage of UV radiation and the exposure time. Overdose or overexposure is possible, however, and can lead to severe burns. It is important to choose a treatment provider who is experienced in the technique. It is also important to tell the physician about all medications being taken by the patient.