Minimal Erythema Dose (MED) in Normal Canine Skin by Irradiation of Narrow-Band Ultraviolet B (NB-UVB)

Abstract

ABSTRACT. Narrow-band UVB (NB-UVB) is light over a very narrow band of wavelengths (around 311 nm) that is concentrated in the therapeutic range and minimally in the sunburn range. It has therefore become the phototherapy treatment of choice for skin diseases. The minimal erythema dose (MED) on canine skin for standardizing dosage schedules in NB-UVB treatment and histopathological analyses were performed in these dogs. In all 32 dogs tested, the MED ranged from 432 to 864 mJ/cm 2 . There were no significant differences in MED among breeds, sex and age groups. Histopathology obtained from areas irradiated by MED showed only mild vascular dilatation. These findings might be valuable for the application of NB-UVB phototherapy to canine skin diseases. Ultraviolet (UV) is invisible light that is part of the energy that comes from the sun [1]. It is made up of three types of rays from the longest wavelength to the shortest: UVA, UVB and UVC. Prolonged exposure to the sun causes skin damage and sometimes skin cancer because of these UV rays. However, scientists have found that although the different wavelengths of light can have adverse effects, they can also be used as UV phototherapy to treat skin diseases [6,13]. UV phototherapy is exposure to intense UV light sources of a specific wavelength or narrow range of wavelengths for specified amounts of time to treat a variety of skin disorders [14,17]. In human medicine, UVA and UVB irradiation has been used successfully to treat a number of diseases, including psoriasis, cutaneous T-cell lymphoma and atopic dermatitis [10,15,16,18].In human medicine, phototherapy devices use either short-wavelength broad-band UVB rays or the long rays of UVA. Broad-band UVB bulbs emit light in a broad range that includes the therapeutic wavelengths specific to the treatment of skin disorders but also is responsible for causing sunburn, which increases the risk of skin cancer. This limits the usefulness of therapeutic broad-band UVB [1]. In contrast, narrow-band UVB (NB-UVB) emits light over a very short range of wavelengths concentrated primarily in the therapeutic range [9]. In addition, NB-UVB phototherapy induces apoptosis of dermal T lymphocytes [12]. Thus, NB-UVB is considered effective for controlling human T-cell-mediated skin diseases such as cutaneous T cell lymphoma or atopic dermatitis [3,7,8,11].The minimal erythema dose (MED) is the minimum dose of radiation that produces perceptible skin erythema, and it is expressed in Joules per square centimeter (J/cm 2 ). The MED must be determined before UV therapy in order to minimize the inflammation of irradiated skin and define the initial irradiation dosage. However, in veterinary medicine, few studies have been published on the effects of the specific band of UV on canine skin. Our aims in this study were to determine the MEDs on normal canine skin in order to standardize dosage schedules in NB-UVB treatment and to determine whether MEDs vary with canine breed, gender, and age. Moreover, to confirm the effect of NB-UVB on dog s...

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