PUVA therapy

Description:
PUVA is an acronym. The P stands for psoralen,(Psoralen is a photosensitizing agent found in plants ) the U for ultra, the V for violet, and the A for that portion of the solar spectrum between 320 and 400 nanometers in wavelength. Psoralens are chemicals found in certain plants that have the ability to absorb ultraviolet light in these wavelengths. Once the light energy is absorbed, these chemicals are energized to interact with DNA, ultimately inhibiting cell multiplication, which is their presumed mode of action.

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Certain skin diseases are characterized by cells that are rapidly multiplying. Inhibiting this unrestrained multiplication can be useful in treating these diseases. So PUVA is a combination of an oral drug and subsequent ultraviolet light exposure. The treatment may affect certain blood cells and skin cells so that the skin disease improves.

It is a 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.

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.

Plant sources   from where  we get psoralens:
Ficus carica (fig) is probably the most abundant source of psoralens. They are also found in small quantities in Ammi visnaga (bisnaga), Pastinaca sativa (parsnip), Petroselinum crispum (parsley), Levisticum officinale (lovage), Foeniculum vulgare (fruit, i.e., fennel seeds), Daucus carota (carrot), Psoralea corylifolia (babchi), and Apium graveolens (celery).

Types of PUVA therapy:
The most common form of therapy combines 8-methoxypsoralen taken by mouth followed 45-60 minutes later by exposure of the skin to UVA. Less commonly the drug is applied topically (the medication is occasionally diluted in bathtub water in which the patient is immersed) and then after a few minutes the ultraviolet exposure occurs.

Procedure:
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.

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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.

How maney PUVA  therapy is required:
There ought to be a significant improvement in the patient’s skin disease after about 15 treatments. Treatments are given no sooner than 48 hours apart because the burn induced by PUVA is often delayed for as long as two days (unlike ordinary sunburns). Unless there is a problem, the amount of energy administered to the patient is increased appropriately at each visit depending on the patient’s coloration. After about 30 treatments, a decision is made as to whether to continue treatments. PUVA is not always effective. If there is no improvement after these treatments, it is probably unlikely that continuing this form of treatment is worthwhile. On the other hand, if significant clearing has occurred, it is probably prudent to decrease the frequency of treatments in order to maintain the improvement. Since there is a relationship between the amount of light energy administered and the degree of photo-aging and the induction of skin cancers, it is wise to limit the light exposures as appropriate.

Advantages:
The major advantage to PUVA is that it is an effective therapy that becomes active only at the site of the disease, the skin. It can be used to treat large areas of skin, and the fact that the drug is only activated in the presence of UV light implies that it may be less toxic than other therapies that require systemic administration and whose effects are not localized to just the skin.

PUVA must be administered in a physician’s office under the control of a medical professional so it requires repeated visits to the office. PUVA may not cure psoriasis permanently so treatment can be required indefinitely.

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 since ancient Egypt but have only been available in a chemically synthesized form since the 1970s.

Resources:
http://en.wikipedia.org/wiki/PUVA_therapy
http://www.medicinenet.com/puva_therapy_photochemotherapy/article.htm

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