DescriptionAn in-depth report on the causes, diagnosis, treatment, and prevention of psoriasis.
Alternative NamesPUVA therapy
Ultraviolet B (UVB) and ultraviolet A (UVA) radiation are primary components of sunlight. UVB is the primary cause of sunburn and primarily affects the outer skin layers. UVA penetrates more deeply and efficiently.
When sunlight penetrates the top layers of the skin, this ultraviolet radiation bombards the genetic material, the DNA, inside skin cells and injures it. It also impairs immune function in the skin. Such effects are the cause of wrinkles, aging skin, and skin cancers. These same damaging effects, however, can also destroy the skin cells that form psoriasis patches.
Phototherapy for psoriasis can be administered as UVA in combination with medications or as variations of UVB radiation with or without medications. Not everyone is a candidate. For example, it may not be appropriate for patients who should avoid sunlight or those with very severe psoriasis.
UVB Therapy. UVB radiation reduces the abnormally rapid skin cell growth that occurs with psoriasis. The current standard treatments using this radiation are either broadband UVB or a newer approach--narrow-band UVB (NB-UVB). Both treatments involve exposure to a light source for a set length of time at regular schedules. Either treatment can be administered at home. Another recent option is the excimer laser that emits a precise wavelength for local areas.
UVA Therapy (PUVA). The treatment using UVA requires a photosensitizing medication (usually psoralen) in combination with UVA radiation to be effective (and therefore the treatment is referred to as PUVA. This approach is very potent and is effective in more than 85% of patients that use it. However, it also poses a higher risk for skin cancers, including melanoma, than UVB.
Psoralens and Ultraviolet A Radiation (PUVA)
PUVA treatments cause inflammation and redness in the skin to develop within two to three days after treatment. Such damage inhibits skin cell proliferation and reduces psoriasis plaque formation. PUVA employs a combination of a psoralen drug and ultraviolet A (UVA) radiation. Forms of psoralen include methoxsalen, 8-methoxypsoralen (8-MOP), or bergapten (5-MOP). The effectiveness of the treatment is based on a chemical reaction in the skin between the psoralen and light, which creates redness and inflammation that prevents the psoriasis disease process.
People should avoid this treatment if they are taking drugs or have conditions that cause them to be light sensitive. They should also take protective measures before, during, and after each treatment.
Initial PUVA Treatment Phase. The initial phase typically follows these steps:
It takes an average of about 25 PUVA treatments for full effect, but during that period, treatment intensity may vary:
Maintenance Phase. Once the psoriasis has improved by about 95%, the patient may be put on a maintenance schedule. Often only one or two treatments a month are needed, but some people may need more frequent treatments. As maintenance continues and the interval between treatments lengthens, the patients may become more susceptible to tanning and sunburn. They should reduce exposure to natural sunlight during this time.
Success Rates. Nearly 90% of patients achieve marked improvement or clearing within 20 to 30 treatment sessions.
Combinations. Effectiveness may be enhanced or response hastened by combining PUVA with oral retinoids, such as acitretin, or drugs such as calcipotriene, methotrexate, or tazarotene gel. In addition, combinations may allow for lower doses of radiation or medications to be used, minimizing side effects. Retinoids may also help protect against skin cancers. On the other hand, methotrexate may increase the risk. In some cases, patients resistant to PUVA or UVB may respond when the phototherapies are combined.
Side Effects and Complications of PUVA. Adverse side effects include the following:
Special Warning on PUVA and Skin Cancers. It has been known for some time that PUVA can modify DNA and cause genetic mutations. PUVA is known to increase the risk for squamous cell skin cancer and slightly increases the risk for basal cell skin cancer, both of which are nearly always curable. The risk for skin cancers is higher in the following patients:
Even more worrisome was a study reporting an increased risk of melanoma, a very serious skin cancer. Discussions are under way, in fact, about discontinuing PUVA for psoriasis. The arguments generally are as follows:
Broadband Ultraviolet B (UVB) Radiation
Broad spectrum UVB is radiation measured at 290 to 350 nm and has been the standard UVB phototherapy treatment in US. It may be administered with or without medications. When used without medication (known as selective ultraviolet phototherapy), UVB treatment generally is administered as follows:
Use of Medication. UVB was commonly used with coal tar (the Goeckerman regimen) in past decades and then with anthralin (the Ingram regimen). Other medications are being investigated with some success and may prove to be more tolerable.
The Goeckerman regimen requires daily treatments for up to four weeks. The coal tar or anthralin are applied once or twice each day and then washed off before the procedure. Studies indicate that a low-dose (1%) coal tar preparation is as effective as high-dose (6%). Such regimens are unpleasant, but still useful for some patients with severe psoriasis, since they can achieve long-term remission (up to six to 12 months).
Some evidence suggests that by using a simple emollient (e.g., Vaseline, mineral oil) that enhanced UVB light penetration can be effective. (This increases the risk for sunburning, however, and care must be taken.)
Combinations of other topical and oral medications are being tried. For example, combining UVB with methotrexate or retinoids, such as a tazarotene gel or oral acitretin, is producing positive results. Combinations with any of these agents, however, must be supervised carefully to avoid adverse reactions.
Side Effects of UVB. The treatment can cause itching and redness. UVB radiation from sunlight is known to increase the risk for skin cancers. There is no strong evidence, however, that UVB treatments pose any risk for skin cancers except on male genitalia, which can be significant (4.5%) at high doses.
Narrow Band Ultraviolet B (NB-UVB) Radiation
Narrow band NB-UVB radiation uses fluorescent lighting that emits radiation in a specific range between 310 and 312 nm, which, theoretically, is the most beneficial component of sunlight. Exposure times are shorter but of higher intensity than with broadband UVB.
Clearance of 75% typically occurs after 10 to 12 treatments. NB-UVB treatments performed three times a week achieve results that are equal to twice-weekly PUVA treatments. (Weekly NB-UVB treatments are not effective.) It is also probably less likely than PUVA to cause skin cancers. Studies are mixed on whether its remissions rates are equal to those of PUVA, but the weight of evidence is currently positive.
Patients prefer this approach over other PUVA treatments because they do not have to wear protective eyewear, take medications, or experience unpleasant side effects, notably nausea. It is also safe for pregnant women and children.
Some experts, then, believe that NB-UVB should be the first choice for patients with chronic plaque, with PUVA reserved for patients who fail.
According to one 2002 study, however, NB-UVB does not have any affect on the disease process itself. In the study NB-UVB radiation only affected the specific areas of skin that it targeted. Given these results, it is not clear, then, if this approach has any significant long-lasting value for treating chronic psoriasis. Combinations with topical agents, such as tazarotene or psoralens, may improve its effectiveness.
Laser UVB Treatment. A recent variation of a device called an excimer laser (Xtrac) delivers a precise UVB wavelength of 308 nm. The excimer laser is more effective than narrow-band UVB (NV-UVB) for localized psoriasis, since it allows targeting of very specific areas of skin. (It is not suitable for the scalp, however.) Generally, eight to 10 treatments administered twice a week are needed to clear psoriasis. Remission rates are similar to NB-UVB, but the excimer laser can clear the psoriasis faster and at lower doses. It also spares the healthy skin around it. Blistering is a common side effect. More comparison studies are needed to determine risk and benefits compared to NB-UVB, particularly any long-term risk for skin cancer.
Pulsed-Dye Lasers. Pulsed-dye lasers emit high-intensity yellow light, which destroy the tiny blood vessels that make up psoriatic plaques. (This treatment has been used for years to remove birthmarks, such as port wine stains, and unsightly blood vessels on the skin.) Some studies have reported significant (but not complete) improvement and remissions that have lasted up to 13 months. Treatments last up to 30 minutes and can feel uncomfortable (similar to being repeatedly snapped with a rubber band). It typically takes up to six sessions to clear the target areas. Bruising is common and there is a small risk for scarring.
Commercial Tanning Units
Home tanning devices and tanning salons are not ordinarily recommended, but they may be helpful for patients without access to a medical unit. In a 2003 study, many patients achieved a significant reduction in symptoms with a combination of acitretin and exposure to a UV-B commercial tanning unit (A Wolff tanning bed). It should be noted, however, that tanning bed and salon standards and UV outputs vary widely. Some units emit UVA radiation, which poses a higher risk for skin cancers. Adverse effects of tanning salons that use UVA or UVB radiation are the same as with any UV phototherapies, including a risk for skin cancer. Experts then do not recommend them except in consultation with a physician or as part of a clinical trial.