Phototherapy: Broadband Ultraviolet B (290-320nm), Narrowband UVB (311nm) and Psoralen with UVA (320-400nm)
Ultraviolet light therapy is one of the most widely used skin-directed therapies for early stage cutaneous T-cell lymphoma (CTCL). Radiation within the ultraviolet B (290- 320 nm) and UVA (320-400nm) spectrums is prescribed for a host of T-cell mediated skin diseases including psoriasis, vitiligo and cutaneous graft-versus-host-disease.
In early stage CTCL, phototherapy is typically selected when skin involvement is diffuse and/or topical treatments have proven to be impractical. The benefits of UVA and UVB have been described for decades as the correlation between CTCL manifestations in covered areas of the body (e.g.,. bather’s trunk, flanks and folds) and sparing in sun-exposed skin was observed.
Patients often share subjective reports of improvement in their skin during the summer months or following a tropical vacation. The mechanism of action for ultraviolet light therapy is broad with effects produced on cell surface membrane proteins causing apoptosis (cell death). In general, UVB reaches the more superficial skin layer of the epidermis, while UVA penetrates deeper into the dermis.
Broad and Narrow Band UVB Therapies
Both broad and narrow band UVB therapies are carried out in dermatology practices equipped with specially calibrated “light boxes.” UVB therapy does not require administration of an oral sensitizing agent in order to produce beneficial effects in the skin. It is a reasonable choice for therapy when the lesions are thin and do not involve the hair follicle (folliculotropic mycosis fungoides).
Patients are exposed to the UVB spectrum in a graduated fashion at increased doses with treatments taking place two to three days per week. The goal of therapy is clinical response with an eventual taper to a more manageable schedule of one day per week.
One of the major hindrances to phototherapy is the time requirements for patient visits, which may disrupt work or home life. In addition, access to a treatment center may be geographically challenging for patients who reside in rural or remote areas. Redness and burning can be problematic in certain fair complexioned individuals; therefore, patients should be assessed prior to each treatment.
Psoralen and UVA (PUVA) Phototherapy
Psoralen and UVA (PUVA) phototherapy involves the combination of the photosensitizing agent 8-methoxypsoralen with UVA light. UVA radiation has a longer wave length than UVB and can penetrate window glass and, likewise, can penetrate the larger and thicker lesions of CTCL.
Patients ingest the psoralen 1 ½ to 2 hours before exposure to an escalating dose of UVA light. Treatments are delivered three days per week initially until a maximal response is achieved.
Over time, patients will reduce the frequency of treatments to a less cumbersome maintenance schedule. Toxicities of PUVA include burning, nausea related to psoralen administration, and increased risk of skin cancers. Patients are expected to wear UVA eye protection up to 24 hours following treatment because of the small but theoretical risk of cataract formation.