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PUVA is an ultraviolet light therapy treatment for eczema, psoriasis, graft-versus-host disease, vitiligo, mycosis fungoides, large-plaque parapsoriasis and cutaneous T-cell lymphoma using the sensitizing effects of the drug psoralen.:686 The psoralen is applied or taken orally to sensitize the skin, then the skin is exposed to UVA.
Photodynamic therapy is the general use of nontoxic light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells. Still, PUVA therapy is often classified as a separate technique from photodynamic therapy.
Psoralens are photosensitizing agents found in plants. Psoralens are taken 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 and vitiligo. Like UVB light treatments, the reason remains unclear, though investigators speculate there may be similar effects on cell turnover and the skin's immune response.
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. The dose will increase in every treatment until the skin starts to respond.
Some clinics test the skin before the treatments, by exposing a small area of the patient's skin to UVA, after ingestion of psoralen. The dose of UVA that produces uniform redness 72 hours later, called the minimum phototoxic dose (MPD), becomes the starting dose for treatment.
At the very least for vitiligo, narrowband ultraviolet B (UVB) phototherapy is now used more commonly than PUVA since it does not require the use of the Psoralen. As with PUVA, treatment is carried out twice weekly in a clinic or every day at home, and there is no need to use psoralen.
Narrowband UVB does not cure the legs and hands, compared to the face and neck. To the hands and legs PUVA may be more effective. The reason can be because UVA penetrates deeper in the skin, and the melanocytes in the skin of the hands and legs is deeper in the skin. The Narrowband UVB does not reach the melanocytes.
Some patients experience nausea and itching after ingesting the psoralen compound. For these patients PUVA bath therapy may be a good option.
Long term use of PUVA therapy has been associated with higher rates of skin cancer.
The most significant complication of PUVA therapy for psoriasis is squamous cell skin cancer. Two carcinogenic components of the therapy include the nonionizing radiation of UVA light as well as the psoralen intercalation with DNA. Both processes negatively contribute to genome instability.
Psoralens have been known since ancient Egypt but have only been available in a chemically synthesized form since the 1970s.