Phototherapy means to treat with light.
When sunlight penetrates the top layers of the skin, this ultraviolet radiation bombards the DNA inside skin cells and injures it. This can cause wrinkles, aging skin, and skin cancers. However, these same damaging effects can destroy the skin cells that form psoriasis patches.
Phototherapy for psoriasis can be given as ultraviolet A (UVA) light in combination with medications, or as variations of ultraviolet B (UVB) light with or without medications. Not everyone is a candidate. For example, phototherapy may not be appropriate for patients who should avoid sunlight or those with very severe psoriasis.
Ultraviolet A (UVA) is a main part of sunlight. UVA phototherapy uses a photosensitizing medication (usually psoralen) in combination with UVA radiation. A photosensitizing medication makes a person more sensitive to light. Treatment with psoralen and UVA is referred to as PUVA. This approach is very powerful and effective in more than 85% of patients who use it. However, it poses a higher risk for skin cancers than UVB.
PUVA treatments cause inflammation and redness to develop in the skin within 2 - 3 days after treatment. Such damage inhibits skin cell proliferation and reduces psoriasis plaque formation.
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 the full effect to be seen, 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 - 30 treatment sessions.
Combinations. Combining acitretin, calcipotriene, methotrexate, or tazarotene gel with PUVA may enhance its effectiveness or increase the response. 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 (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.
Special Warning on PUVA and Skin Cancers. It has been known for some time that PUVA can change DNA and cause genetic mutations. PUVA is known to increase the risk for squamous cell skin cancer and slightly increase the risk for basal cell skin cancer, both of which are nearly always curable. One study reported an increased risk of melanoma. The risk for skin cancers is higher in people who have:
Discussions are under way about discontinuing PUVA treatment of psoriasis, for the following reasons:
Side effects of UVA radiation can be severe. Protective measures are needed during, before, and after treatment. Patients should avoid prolonged exposure to the sun for 24 hours before the oral treatment starts.
Protective Measures During Treatment:
The following safety features should be available in the PUVA chamber:
Protective Measures After Treatment. The drugs used in PUVA make patients more likely to get a natural sunburn for a few hours after treatment. Patients should take the following precautions:
Ultraviolet B is another main part of sunlight, and is the main cause of sunburn. It generally affects the outer skin layers. UVB radiation reduces the abnormally rapid skin cell growth that occurs with psoriasis.
Types of UVB therapy:
Broad spectrum or broadband UVB is radiation in the wavelength of 290 - 350 nanometers, and is the standard UVB phototherapy treatment in the United States. It is not as potent as the treatments that use narrow-band UVB or PUVA, and is not useful for chronic psoriasis.
Broadband UVB may be given with or without medications. When used without medication (known as selective ultraviolet phototherapy), UVB treatment is generally given 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 studied with some success, and may prove to be better tolerated.
The Goeckerman regimen requires daily treatments for up to 4 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 a high-dose (6%) preparation. Such regimens are unpleasant, but are still useful for some patients with severe psoriasis, because they can achieve long-term remission (up to 6 - 12 months).
Some evidence suggests that using a simple emollient (such as Vaseline or mineral oil) that enhances UVB light penetration can be effective. This addition to the treatment increases the risk for sunburns, however, and patients must be careful to avoid sun exposure. Researchers are trying combinations of other topical and oral medications. 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 drugs, however, must be supervised carefully to avoid serious 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 that UVB treatments pose any risk for skin cancers except on male genitals. This risk, however, can be significant (4.5%) at high doses.
Narrow-band radiation may be safer than other approaches, and some experts now believe it should be the first option for patients with chronic plaque psoriasis.
NB-UVB is used without medications and is very strong. Whether it has any effect on the disease process itself is unclear. The light wavelength is between 310 - 312 nanometers, which is the most beneficial part of sunlight.
Exposure times are shorter, but of higher intensity than with broadband UVB. This therapy is probably less likely than PUVA to cause skin cancers.
Clearance of 75% typically occurs after 10 - 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. Studies so far are mixed on whether NB-UVB remission rates are equal to those of PUVA.
Patients prefer NB-UVB over other PUVA treatments because they do not have to wear protective eyewear, take medications, or experience unpleasant side effects such as nausea. NB-UVB is also safe for pregnant women and children.
Combinations with topical medications, such as tazarotene or psoralens, may help NB-UVB therapy work more effectively.
Laser UVB Treatment. A variation of a device called an excimer laser (Xtrac) delivers a precise UVB wavelength of 308 nanometers. The laser is more effective than narrow-band UVB for localized psoriasis, because it allows very specific areas of skin to be targeted. (Note: The therapy is not suitable for the scalp.) Generally, 8 - 10 treatments given twice a week will clear psoriasis. Remission rates are similar to those of 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 give off high-intensity yellow light, which destroys 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. Treatment sessions last for 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.
Home tanning devices and tanning salons are not usually recommended, but they may be helpful for patients who do not have access to a medical unit. Many patients have achieved a significant reduction in symptoms when taking acitretin and exposed to a UVB commercial tanning unit (specifically, a Wolff tanning bed).
However, UV outputs can vary widely among tanning beds and salons. 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.
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