MeSH D011701 | ||
PUVA (psoralen and ultraviolet A) 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. The psoralen is applied or taken orally to sensitize the skin, then the skin is exposed to UVA.
Contents
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.
Procedure
Psoralens are materials that make the skin more sensitive to UV light. They are photosensitizing agents and are found in plants naturally and also manufactured synthetically. Psoralens are taken as pills (systemically) or can be applied directly to the skin, by soaking the skin in a solution that contains the psoralens. They allow UVA energy to be effective at lower doses. When combined with exposure to the UVA in PUVA, psoralens are highly effective at clearing psoriasis and vitiligo. In the case of vitiligo, they work by increasing the sensitivity of melanocytes, the cells that manufacture skin color, to UV light. Melanocytes have sensors that detect UV light and trigger the manufacture of brown skin color. This color protects the body from the harmful effects of UV light. It can also be connected to the skin's immune response.
The physician can choose a starting dose based on the patient's skin type. The dose will increase in every treatment until the skin starts to respond, normally when it becomes a little bit pink.
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 12 hours later, called the minimum phototoxic dose (MPD), or minimal erythema dose (MED) 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 is less effective for 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.
Side effects and complications
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.
History
Psoralens have been known at least since ancient Egypt. In the 1890s Niels Ryberg Finsen of Copenhagen developed a bulky phototherapy machine to treat skin diseases using UV light. In 1900, French electrical engineer, Gustave Trouvé miniaturized Finsen’s machine with a series of portable light radiators to heal skin diseases such as lupus and epithelioma. Such machines have only been available in a chemically synthesized form since the 1970s.