The Dermalite UV light machine (National Biological, Beachwood, Ohio) was used as the source of UV radiation. The amount of UV-A and UV-B penetrating the nail plate was measured using a radiometer and compared with a control. Setting: Academic phototherapy clinic. Patients: Ten cadaver fingernails were obtained from 1 cadaver from the National Disease Research Interchange. Because the objective was to determine transmission through normal fingernails, grossly diseased or deformed nails were not used. Main Outcome Measures: The percentage of UV light penetration through each fingernail was calculated by dividing the amount of radiation measured when the fingernail was in front of the light by the amount of radiation measured when there was nothing in front of the light (UV with nail divided by UV without nail). Results: All 10 fingernails completely blocked the UV-B light, reading 0 mW/cm 2 on the radiometer. The mean penetration of UV-A light through the fingernails was 1.65%, ranging from 0.56% for the right fifth digit to 2.43% for the left second digit. Conclusions: The nail plate completely blocked UV-B light, and only a minimal amount of UV-A light penetrated the nails. If UV is required to directly penetrate the nail to treat nail bed psoriasis, then these data suggest that therapeutic efficacy may be compromised by the intervening nail plate. This minimal penetration of UV-A light may explain why therapies such as psoralen-UV-A (PUVA) have low efficacy for the treatment of nail psoriasis.
Calcitriol ointment has been approved for the treatment of psoriasis in many countries around the world. It may be prescribed in conjunction with phototherapy. Our purpose was to evaluate the effect of various therapeutic ultraviolet modalities on the stability of calcitriol and, conversely, to study the effects of calcitriol ointment on transmission of different forms of ultraviolet light. Calcitriol ointment 3 microg per g was irradiated with 10 J per cm2 ultraviolet A, 100 mJ per cm2 broadband ultraviolet B, and 3.0 J per cm2 narrowband ultraviolet B, and its stability was compared with samples exposed to fluorescent light and ambient sunlight. Ultraviolet A and ultraviolet B transmission were measured through thin and thick layers of calcitriol 3 microg per g ointment and vehicle. More than 90% of calcitriol ointment is degraded upon exposure to ultraviolet A, broadband ultraviolet B, and narrowband ultraviolet B. Transmission of ultraviolet A is reduced through calcitriol ointment and its vehicle by 17%-31% and 17%-41%, respectively. Transmission of ultraviolet B is reduced by 67%-87% through vehicle and 50%-83% through calcitriol ointment. When used in conjunction with phototherapy, calcitriol ointment should be applied after ultraviolet exposure, not before. Calcipotriene, the only vitamin D analog already approved for psoriasis in the USA, has been used successfully in combination with ultraviolet B and psoralen plus ultraviolet A.
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