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Simple changes to PUVA phototherapy may minimize the photocarcinogenic risks

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Page 1: Simple changes to PUVA phototherapy may minimize the photocarcinogenic risks

Photodermatol Photoimmunol Photomed 1999: 15: 205 Copyright C Munksgaard 1999Printed in Denmark ¡ All rights reserved

ISSN 0905-4383

Letter to the editor

Simple changes to PUVA phototherapy mayminimize the photocarcinogenic risks

Psoralen plus ultraviolet A (PUVA) is a powerfultherapy for psoriasis. The work of Rob Stern andothers has emphasized the risks of life-long treat-ment of the disease (1, 2). The following are simpleways to minimize the photocarcinogenic risks as-sociated with phototherapy.

1. Up to 5% of the output of PUVA lamps canbe UVB radiation. UVB may be considered asignificant co-carcinogen that plays a smalltherapeutic role (3). It is technically feasible tocompletely filter out the UVB, at a small ex-pense. Minimizing the UVB output of PUVAunits should be required of PUVA unit andlamp manufacturers.

2. Patients subjected to high cumulative doses ofradiation are at a higher carcinogenic risk. Theminimum photoxic dose (MPF) of patient in-creases with successive PUVA treatments, oftenin unpredictable ways. To minimize the inci-dence of phototoxic events (burns), a dose sig-nificantly lower than the MPD is chosen. Thisleads to a greater number of treatments, andsignificantly increased cumulative UV doses.

The only reliable measure of the individualpatient’s MPD is a phototest, which is time-consuming and, in many instances, not reim-bursable by HMO (health maintenance organ-ization) plans. In most instances in the UnitedStates, the starting dose is based on the patient’sskin phototype and pigmentation level. Theseuseful markers for UV penetration are not pre-dictive measures of drug uptake in the epider-mis, leading to imprecise dosimetry. PUVAtreatment guided by frequent phototests, ap-proximately once a week, results in more rapidclearing at higher individual UVA doses, and31% lower cumulative doses (4). This can be asignificant safety factor for the patient who isdependent on PUVA. While phototesting istime-consuming, devices such as a luminairewith metallic grids (5) or neutral density filters

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make such tests minimally demanding of staffor equipment resources.

3. PUVA is responsible for accelerated photoagingof nonlesional skin, and photoaging has beenassociated with the induction of skin cancer.There are products available, such as retinoicacid and its derivatives, alpha-hydroxy acids,and others that claim to reverse skin photodam-age. We need to find ways that photodamage-reversal products may be implemented betweenPUVA protocols during remission, to minimizethe risk of accelerated photoaging and photo-carcinogenesis.

PUVA is an effective therapy for patients withpsoriasis. With the photocarcinogenic risks betterdefined, the dermatologic community needs tocontinue to fine tune the available technology andtreatment protocols to improve the long-term pa-tient outcomes.

References

1. Morrison WL. Variations of PUVA: Practical and effective?Arch Dermatol 1998: 134: 1286–1287.

2. Stern RS, Nichols KT, Vakeva LH. Malignant melanomain patients treated for psoriasis with methoxsalen (psora-len) and ultraviolet A radiation (PUVA). The PUVA Fol-low-Up Study. N Engl J Med 1997: 336: 1041–1045.

3. Schothorst AA, Slaper H, Schouten R, Suurmond D. UVBdoses in maintenance psoriasis phototherapy versus solarUVB exposure. Photodermatol 1985: 2: 213–220.

4. Carabott FM, Hawk JL. A modified dosage schedule forincreased efficiency in PUVA treatment of psoriasis. ClinExp Dermatol 1989: 14: 337–340.

5. Diffey BL, Oliver RJ. An inexpensive luminaire for diag-nostic phototesting to UVB radiation. Photodermatol1985: 2: 260–262.

Nikiforos Kollias, PhDWellman Laboratories of PhotomedicineMassachusetts General Hospital55 Fruit Street – BHX 630Boston, MA 02114USA