PUVA Therapy (Photochemotherapy)

PUVA is an acronym. The P stands for psoralen, 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 the UVA portion of the solar spectrum. Once the light energy is absorbed, these psoralens are energized to interact with DNA, ultimately inhibiting cell multiplication, which is its presumed mode of action.

Certain skin diseases are characterized by cells that are rapidly multiplying. Inhibiting this unrestrained proliferation can be useful in treating these diseases. So PUVA is a combination of an oral drug and subsequent ultraviolet light exposure.

One of the skin diseases for which PUVA is used and for which it was originally developed is psoriasis. The psoralen, 8-methoxypsoralen (8-MOP) (Oxsoralen), is used for the treatment of psoriasis along with exposures to ultraviolet light in the UVA spectrum. PUVA is also of benefit in treating vitiligo, mycosis fungoides (cutaneous T-cell lymphoma), and graft versus host disease.

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.

The major advantage to PUVA is that it is an effective therapy that becomes active only at the site of exposure. 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.

Since PUVA must be administered under a physician's supervision, it requires repeated visits to the office or clinic. PUVA does not cure psoriasis so treatment may be required indefinitely.

The psoralen medication is taken 45-60 minutes prior to the ultraviolet light exposure. The amount of the psoralen is based on the weight of the patient. The length of the exposure depends on the degree of the patient's pigmentation. Accordingly, the darker the patient, the longer the exposure time. Depending on the equipment used, the exposure may occur in a metal light box surrounding the patient with the bulbs that run vertically and are generally 48 inches long and resemble fluorescent bulbs. In newer boxes, there is an integrated light meter that enables the operator to administer the desired amount of energy with an automatic shut off after that dosage of light is achieved.

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 (if there is one) 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.

PUVA has a definite potential to cause skin cancer, including melanomas. The risk of developing skin cancer is directly related to the amount of energy administered. PUVA will cause photo-aging (dry and wrinkled with pigment alterations called lentigenes) that is unavoidable. If not appropriately monitored, PUVA can produce severe ultraviolet light burns. Occasionally, Oxsoralen can cause nausea so susceptible patients take the drug with food.

PUVA is a safe and effective treatment for psoriasis. Recently, a newer treatment has supplanted it to some extent, utilizing a different wavelength of light called "narrow band UVB." Although a visit to a physician's office is still necessary to administer the light, it is not necessary to take a drug by mouth. Both types of treatments are similar in their effectiveness.

PUVA is also useful in the treatment of cutaneous T-cell lymphoma, mycosis fungoides, and certain difficult cases of atopic dermatitis. Extracorporeal photophoresis is a variation of PUVA where a portion of the patient's white blood cells are removed and then mixed with a psoralen preparation prior to exposure to a UVA source in a machine external to the body. These treated cells are then infused back into the patient. This type of treatment is effective for patients with Sézary's syndrome, a type of leukemic mycosis fungoides, as well as graft vs. host disease.

National Psoriasis Foundation
https://www.psoriasis.org/