Psoriasis is a chronic inflammatory disease of the skin with no permanent cure. Its symptoms of pain and itching can put the patient in a lot of suffering.
Mild cases can obtain relief with the use of over the counter or prescription topical creams and lotions.
However, moderate to severe cases of psoriasis need a more aggressive treatment, which can involve combination therapy with topical application, oral medication, and phototherapy.
PUVA is a type of phototherapy in which psoralen is given to the patient either in oral form or as a topical application and then the psoriasis skin lesion is exposed to the UVA rays.
So, essentially, PUVA is a combination of an oral or topical photosensitizing drug and subsequent ultraviolet light A exposure.
PUVA for psoriasis
- PUVA medical abbreviation for Psoralen Ultra Violet A (rays)
PUVA is a therapy for skin diseases with light sensitizing drug Psoralen and ultraviolet A rays. It is used in the treatment of psoriasis, eczema, vitiligo, and some other skin conditions.
Like ultraviolet B (UVB), ultraviolet A (UVA) is also present in sunlight. But, UVA has a longer wavelength than UVB and is ineffective when used alone. However, when its use is combined with a photosensitive drug such as psoralen, it proves effective.
This is a specialized treatment, which is also referred to as photochemotherapy as it combines treating psoriasis with phototherapy (here UVA is used and not UVB) and a photosensitization drug. The light sensitizing drug in PUVA is called psoralen.
Psoralen is given first before exposure to artificial UVA light. This is done because psoralen makes the skin psoriasis more responsive to UVA light, thereby allowing smaller doses of UVA to be used.
UVA light is used instead of UVB because UVA light penetrates deeper into the skin than UVB. This makes this treatment more aggressive and effective and the choice for more severe forms of psoriasis.
PUVA treatment is seen to be most effective against stable plaque psoriasis, guttate psoriasis, and psoriasis of the palms and feet.
Psoralens are a group of natural furocoumarins, which are derived from Ammi Majus, a plant found in Egypt. They are also found present in celery, carrots, parsley, parsnip, and other vegetables.
Psoralen is given as oral pills or as a topical lotion or as a psoralen bath. After a short period, the skin is exposed to UVA light. UVA is a special wavelength of light, which is “weaker” than UVB.
As explained above, Psoralen is a photosensitive drug, which makes the skin more responsive to UVA rays. This facilitates lower doses of UVA to be used in treatment.
Psoralen tablet is taken 2 hours before light therapy with UVA. Alternatively, topical Psoralen (Gel or cream) can be applied over the skin 30 minutes before UVA is given. An added option is to add Psoralen to the bath and soak in it for about 15 minutes.
How PUVA acts? Mechanism of action
Psoralen interacts with ultraviolet A rays in the epidermis of the skin to form DNA photo-adducts. This resulting photo compound
- Slows down the proliferation of the epidermal cells and
Suppresses the autoimmune reaction on the skin cells
Dosage of PUVA
Therapy with PUVA is given 2 or 3 times a week for a number of weeks, which are decided by the attending practitioner. Doses of UVA light are administered in a physician’s office so that he or she can gradually increase the light exposure time with each session.
The dose is determined by the physician after studying the psoriasis and its type. To determine the starting dose, the following is done:
After taking oral Psoralen by the patient, a small area of the skin is exposed to UVA. The dose that produces uniform redness of the skin after a period of 72 hours becomes the starting point of treatment. It is called the minimum phototoxic dose (MPD).
For UVA treatment, the patient is required to stand in a UVA cabinet for a period of a few seconds to a few minutes.
If oral psoralen has been taken, you will need to wear UVA protection sunglasses as like skin, psoralen also sensitizes your eyes. It is, therefore, necessary to wear these glasses to prevent the formation of cataracts. These glasses should be worn for about 12 to 24 hours after oral psoralen has been taken.
The affected sites are outlined with a skin marker and the surrounding skin is protected from exposure.
Side effects of PUVA
The PUVA combination proves to have the highest risks of side effects.
Short-term side effects include itching and burning of the skin, nausea, and headache.
Long-term side effects include dry skin, wrinkles, and risk of skin cancer including melanoma.
Due to its skin cancer risk, long-term use of this therapy is not advised. Patients who experience nausea and itching with oral psoralen can be switched over to topical or Psoralen baths.