Phototherapy and Photochemotherapy

Ultra violet (UV) rays can be used for the purpose of treatment, either alone (generally UV-b rays are used) or in combination with topically applied agents, as is used in treatment of psoriasis and atopic dermatitis, for inducing remission and health state of skin. When UV is combined with a topically applied agent or systemically administered agent, than it is called photochemotherapy.

Examples of photochemotherapy in psoriasis:

Topically applied psoralens or systemically administered psoralens (psoralens are tricyclic furocoumarins which if intercalated into DNA and exposed to UV-A eventually form DNA cross-links) are combined with UV-A (called as PUVA) is effective in treating psoriasis and in the early stages of cutaneous T cell lymphoma and vitiligo. The structural changes that occur in DNA thought to decrease DNA synthesis and is responsible for the improvement that is seen in psoriasis. But how PUVA (psoralen ultra-violet-A) photochemotherapy is useful in cutaneous T cell lymphoma is not clearly understood.

PUVA photochemotherapy can also stimulates epidermal thickening and melanin synthesis in the skin. This is the reason why PUVA photochemotherapy is used in treatment of vitiligo (complete depigmentation of skin due to absence of melanin pigment). The best treatment that is available for vitiligo is probably the use of oral 8-methoxypsoralen and UV-A. But for promoting satisfactory re- pigmentation there may be requirement of as many as 100 cycles of treatments which may extent up to 18 months.

Side effects of photochemotherapy:

The major side effects of long-term UV-B phototherapy and PUVA photochemotherapy are similar to those seen in individuals with chronic exposure to sun. The side effects of chronic sun exposure are skin dryness, actinic keratoses, and an increased risk of skin cancer.

But most important despite the risk of potentially serious side effects of long term use of photochemotherapy is that the results obtained are excellent.

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