Psoriasis - Phototherapy

Phototherapy

Phototherapy means to treat with light.

When sunlight penetrates the top layers of the skin, the 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.

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Psoralen and Ultraviolet A Radiation (PUVA)

Ultraviolet A (UVA) is a main part of sunlight. PUVA therapy 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 treatment with UVB.

PUVA treatments cause inflammation and redness 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 the 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:

• Psoralen is typically taken by mouth in the form of 8-methoxypsoralen (for example, Oxsoralen) 75 minutes to 2 hours before the treatment starts. Psoralen reaches the skin through the bloodstream, where it increases the skin's sensitivity to UVA radiation.
  • Topical preparations of psoralen are alternatives to pills. They can be "painted on" or applied to the affected areas by soaking or bathing in a psoralen solution. PUVA-bath therapy may be especially useful for persistent psoriasis on the palms and soles, or for patients with liver disease or who get severe nausea from taking the pill form. UVA should be given within 15 minutes of using topical psoralen.
• The patient enters and stands in a light box -- a unit lined with ultraviolet lamps. The initial UVA exposure time is very short (seconds to several minutes), and then increases to 20 minutes or longer. The amount of time a person is exposed to UVA rays depends on the skin type, with the shortest times recommended for fair-skinned patients.