Psoralen and UVA light therapy (PUVA), which combines UVA exposure and a medicine (called a psoralen) that makes your skin more sensitive to light and useful for localised palmoplantar pustular psoriasis PUVA (the use of psoralen medicines with UVA light therapy) is usually used when psoriasis is disabling and safer treatments have not worked. It’s known that coumarin deravatives (psoralen) from ammi majus (medicinal plant) associated with UV light used in treatment psoriasis through many effects ,for example it’s a planner compound can interact with DNA molecules: it was reported that interstrand cross –links are formed in native DNA by irradiation with 360 nm light in the presence of psoralen ,and suggested that the cross-link may result from the reaction of an excited psoralen molecule with pyrimidine bases in opposite strands of the DNA duplex. Only linear psoralens such as psoralen, 8-methoxy psoralen, 5-methoxypsoralen and the synthetic 4,5' -8-trimethylpsoralen (TMP) are used in photo chemotherapy.
There is a bath PUVA and an oral PUVA. Bath PUVA therapies involve soaking in a bath of psoralens liquid for 15 minutes prior to UVA treatment. Oral PUVA involves taking an oral psoralens capsule the day prior to a UVA treatment. Oral psoralens such as methoxsalen cause nausea in many patients. Other adverse effects of PUVA include photosensitivity, which necessitates the use of eye protection and UVA-blocking sunscreen for 24 hours after a PUVA treatment; macular melanosis at exposed sites (PUVA lentigines); and increased risk of skin cancers, especially squamous cell carcinoma.
PUVA has been used in conjunction with other topical agents to increase treatment efficacy. Calcipotriol when added to a regimen of PUVA may reduce the number of PUVA treatments and the total UVA dosage needed for clearing lesions. The rate ratio for marked improvement in patients receiving PUVA plus calcipotriol versus PUVA alone was 1.2 in a recent meta-analysis of 11 controlled studies. If calcipotriol and PUVA are used together, calcipotriol must be applied after PUVA, since irradiation with UVA will inactivate calcipotriol. One small study of PUVA with tazarotene in 12 patients with extensive plaque psoriasis showed a statistically significant improvement after 3 weeks; however, UVA doses should be reduced by at least one-third if tazarotene is added, since it increases the risk for immediate pigment darkening caused by UVA. Coal tars are photosensitizing and are not generally used with PUVA, and PUVA plus topical corticosteroids have yielded conflicting results.
Rotational therapy / Sequential (i.e., rotating systemic drug interventions in a sequential manner) is a means to minimize drug-associated toxicities, since systemic agents for psoriasis often have differing toxicities. This may be considered for psoriasis patients who require systemic treatments long-term to manage their condition. Systemic therapies are optimally used in a rotating fashion to minimize drug toxicities (e.g., methotrexate–acitretin–cyclosporine or methotrexate–PUVA–acitretin) Sequential therapy involves rapid clearing of psoriasis with aggressive therapy (e.g., cyclosporine), followed by a transitional period in which a safer drug such as acitretin is started at maximal dosing. Subsequently, a maintenance period using acitretin in lower doses or in combination with UVB or PUVA can be continued.
You must be aware with these risks when using this therapy
Skin cancer. UVB is the part of sunlight that causes suntans, sunburns, skin damage, and aging. Exposure to UVB light can also lead to skin cancer and can cause serious eye damage. The risk of skin cancer increases with the amount of exposure to UV light. Your dermatologist will monitor your overall exposure to UV rays
Skin damage. Long-term exposure to UVA light may lead to skin damage, aging, skin cancer, and cataracts. This risk of cataracts can be reduced by regular use of sunglasses that block UVA light when you are outdoors. Cancer, The male genitals are highly susceptible to the cancer-causing effects of both PUVA therapy and UVB therapy. For people who have erythroderma or pustular psoriasis, UV treatment may make the condition worse.
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