Psoriasis – Phototherapy

Phototherapy is a treatment option for some patients with Psoriasis.  There are various light sources that can deliver radiation that can slow the growth of keratinocytes (skin cells) in Psoriasis.  Narrow Band UVB is one of the most common and effective light sources for treating Psoriasis.  It delivers UVB light at 311nm which the Psoriasis has the most optimal response.  Typically, patients have treatment sessions 3 times per week for 2-3 months and then gradually taper the number of sessions to a maintenance regimen.  UVA is also used as a light source but must be combined with a photosensitizing agent called a psoralen.  Psoralens can be applied topically or taken internally.  Three types of psoralens are methoxsalen, 5-methoxypsoralen, and trisoralen.  Patients must wear eye protection during the procedure and a day or two afterwards to prevent ocular damage.  The psoralens also make patients sensitive to sunlight so skin sun protection is also mandatory.  Psoralens can cause nausea and must not be taken during pregnancy or while breast feeding.  Itching is also a common side effect of PUVA.  An excimer laser can be used to deliver focused Narrow Band UVB to Psoriasis plaques.  Sunlight also helps Psoriasis but is much more difficult to control the dose of radiation delivered so is not a recommended alternative to the more standard Phototherapies.  All patients on Phototherapy should be counselled about photoaging and the increased risk of skin cancer with this modality.