Photochemotherapy is a special treatment that combines long-wave UV light with psoralen. The procedure is also known as PUVA (psoralen plus UVA).
What is photochemotherapy?
Photochemotherapy is one of the medical procedures in dermatology. It belongs to the light therapies. Photochemotherapy belongs to the medical procedures of dermatology. It belongs to the light therapies. During the treatment, long-wave UV light (UVA) is combined with psoralen, which is a basic molecular substance for various natural substances. The therapy is therefore also called Psoralen plus UVA (PUVA). The natural active ingredient psoralen is contained in the essential oils of some plants. Psoralen has the property of sensitizing the human skin to UV light. Photochemotherapy treatment can make the skin more sensitive to subsequent irradiation with UVA. In this way, the photosensitizing properties can be used for medical treatments. Photochemotherapy was already used about 3000 years ago in ancient India and Egypt to treat white spot disease (vitiligo). For this purpose, plant extracts were rubbed into the skin of the patients. This was followed by irradiation with natural sunlight.
Function, effect, and goals
In dermatology, where photochemotherapy is used, a distinction is made between two forms of treatment. These are topical as well as systemic PUVA therapy. In the context of the topical Photochemotherapie exclusively the treatment of the affected skin places takes place. A cream containing psoralen is used to coat smaller areas of skin. The cream is then absorbed under a film. An alternative is the so-called bath PUVA. Here, the psoralen can accumulate in the skin during a bath with warm water. The full or partial bath lasts 30 minutes. The light sensitization is carried out immediately and has a duration of action of about 30 minutes. During this period the UV treatment takes place. We speak of systemic PUVA therapy when the psoralen is distributed over the whole body of the patient. Two hours before the irradiation therapy, the patient must take tablets containing psoralen. Photochemotherapy is one of the most effective light therapies. In the early 1970s, PUVA therapy became established for the treatment of psoriasis. The positive effect is attributed to the reduction of the pathological cell division rate as well as a supriming effect on the skin defense system. Other areas of application of photochemotherapy are diseases of the skin such as vitiligo, neurodermatitis, mastocytosis and lichen ruber planus. PUVA therapy can also be used to treat cutaneous T-cell lymphomas, which include Sézary syndrome and mycosis fungoides. In addition, photochemotherapy is an alternative to UVA1 therapy used for urticaria pigmentosa. Despite opinions to the contrary, PUVA treatment does not achieve a positive effect in acne. Before starting photochemotherapy, the physician must thoroughly examine the patient’s skin and rule out any photosensitivity that may be caused by specific medications. The same applies to malignant skin tumors. During the examination, the minimum phototoxic dose (MPD) is also determined. The MPD value can be used to indicate the level of UV dose above which reddening occurs on the skin with photosensitizer. Once the psoralen has developed its effect, irradiation of the skin begins with 20 to 30 percent of the minimum phototoxic dose, which is gradually increased in the further course of PUVA therapy. To prevent damage to the eyes during treatment, the patient must protect them with special glasses. Photochemotherapy always takes place on two consecutive days. After that, there is a break day. In total, PUVA therapy comprises 10 to 30 sessions. In a topical cream PUVA treatment, the physician first applies the light sensitizer 8-methoxypsoralen, using a water-in-oil emulsion. After an exposure time of between 20 and 30 minutes, irradiation with long-wave UVA light can take place. This procedure is considered to be particularly suitable for the treatment of hand eczema, which has a smaller surface area.Bath PUVA therapy is carried out in 8-methoxypsoralen solution, which has a concentration of 0.5 to 1.0 mg/l. The water should be between 32 and 37 degrees Celsius. After the bath, PUVA irradiation must be done immediately. It is recommended to perform the treatment three to four times a week.
Risks, side effects and dangers
Although photochemotherapy is considered very effective, it also carries the risk of risks and side effects, since it is an exceedingly intense light therapy. For example, there may be a risk that the UV light has a carcinogenic effect. It is also not uncommon for a phototoxic reaction to occur. This refers to a type of sunburn that results from the increased sensitivity to light. Other possible side effects include keratitis (inflammation of the cornea) or conjunctivitis (inflammation of the conjunctiva) of the eye, the formation of liver spots, and light-induced aging of the skin. PUVA bath therapy should not be used on children under 12 years of age and pregnant women. The same applies to people suffering from severe heart diseases or who have had skin cancer before. If immunosuppressants such as ciclosporin are taken at the same time, there is a risk of severe skin burns and damage to underlying tissue. Systemic photochemotherapy in particular, which involves taking tablets, has a high risk of side effects, including nausea and damage to the liver. For this reason, this procedure is now rarely used.
