Ultraviolet B (UVB) Phototherapy

Type:Uv phototherapy   Time:2017-01-03 15:59:29

 

Kelly KyungHwa Park1 and Jenny Eileen Murase1,2

 

1University of California San Francisco

Department of Dermatology, San Francisco, California

 

2Palo Alto Foundation Medical Group

Department of Dermatology, Mountain View, California

 

USA

 

1. Introduction

 

Vitiligo is a common, acquired pigmentary disorder of unknown pathogenesis that presents a therapeutic challenge to many dermatologists (Figure 1). Although surgery in the form of grafting or transplantation is generally the most definitive treatment option, these procedures are limited by concerns of post-procedure cosmesis. Photochemotherapy using psoralen and ultraviolet A (PUVA) therapy, topical and oral immunosuppresants, as well as cosmetic camouflage are also commonly employed with varying clinical efficacy. Phototherapy is a popular treatment option, which includes both of the generalized ultraviolet B (UVB) therapies, broadband UVB (BB-UVB) and narrowband UVB (NB-UVB). The UVB-based therapeutic modalities in development are targeted delivery of BB- and NB-UVB, monochromatic excimer light (MEL), microphototherapy, and combination therapy. In particular, the sophisticated devices that utilize MEL can emit coherent 308-nm radiation using the xenon chloride (XeCl) excimer laser or microphotography, while incoherent radiation can be supplied by various lamp and light systems. All of the UVB phototherapy modalities can be used in combination with topical or systemic agents, thus further expanding treatment options for vitiligo patients.

 

 

2. History

 

The use of ultraviolet (UV) irradiation was introduced into the field of dermatology in the 1800s after its Nobel Prize-winning application in lupus vulgaris (Roelandts, 2002). By 1928, UV radiation was used in the Goeckerman regimen as part of the classic crude coal tar and phototherapy treatment for psoriasis. Decades later in 1978, BB-UVB phototherapy was developed and used for psoriasis and pruritus. NB-UVB originated in Europe in 1988 indicated for psoriasis, and soon became widely used in the United States in the 1990s. Its innovative use in vitiligo came nearly a decade later in 1997 (Wiskemann 1978; Westerhof and Nieuweboer-Krobotova, 1997). The pivotal study introducing NB-UVB use in vitiligo demonstrated that more patients undergoing NB-UVB had repigmentation of vitiligo patches than those who underwent PUVA photochemotherapy (67% vs. 46%) (Westerhof and Nieuweboer-Krobotova, 1997). Since then, the use of UVB for vitiligo has become


 

 

 

 

 

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70 Vitiligo ¨C Management and Therapy

 

commonplace, and new technologic developments in UVB therapy are continuously underway. The use of MEL with the excimer laser was first described in 1997 (Bonis, Kemeny et al., 1997).

 

3. Theory and mechanism of action

UVB phototherapy consists of the use of artificial light without the use of adjunct photosensitizing agents. It is used for a variety of dermatological conditions, including psoriasis, atopic dermatitis and other eczematous disorders, pruritus, graft-versus-host-disease, lichen planus, and seborrheic dermatitis, among others. In vitiligo, UVB phototherapy ideally results in repigmentation, disease control, and prevention of progression of vitiligo through its immunosuppressive and immunomodulatory properties. UVB is available for use in vitiligo as BB-UVB (290-320 nanometers, nm), NB-UVB (310-312 nm), and monochromatic excimer light (MEL, 308 nm). Although the action spectrum or wavelength(s) specifically targeting vitiligo has yet to be determined, both BB- and NB-UVB as well as MEL have been demonstrated to be clinically effective.

 

The mechanism of how UVB works in vitiligo is unknown. It is established that distinct UVB radiation wavelengths target particular chromophores in the skin, in particular keratinocytes and melanocytes in the epidermis and fibroblasts in the dermis, and facilitate the therapeutic mechanisms of the light depending on chromophore type and function. In the case of UVB, these include apoptosis induction, T-cell depletion, decreased antigen presentation, and the ability to regulate inflammatory mediators and cytokines (Novak, Bonis et al., 2002; Novak, Berces et al., 2004; Weichenthal and Schwarz, 2005).

 

UV, in particular, NB-UVB, is presumed to stimulate dopa-lacking amelanotic melanocytes in the outer root sheaths of hair follicles to produce melanin (Cui, Shen et al., 1991; Norris, Horikawa et al., 1994). It also activates melanocyte migration to adjacent depigmented areas, causing perifollicular repigmentation (Cui et al., 1991; Norris et al., 1994). Furthermore, NB-UVB and MEL (coherent and incoherent) were both found to upregulate endothelin-1 (ET-1) release from keratinocytes, which is thought to play a role in UVB-related melanocyte synthesis and migration (Noborio, Kobayashi et al., 2006). This action is directly dependent on UVB radiation dose, and may account for the particular effectiveness of the 308 nm and

 

 

 

 

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310-312 nm wavelengths (Noborio, Kobayashi et al., 2006). Also, the 308 nm wavelength of MEL is most specific for lymphocyte DNA alteration (de With and Greulich, 1995). The quantitative induction of T-cell apoptosis is greater with excimer laser (MEL) than with conventional BB- or NB-UVB phototherapies. It is thought that the capability to induce T-cell apoptosis is an indicator of clinical efficacy (Ozawa, Ferenczi et al., 1999). Furthermore, keratinocytes may be influenced to release other unidentified cytokines and factors, which suggests that UVB functions as an immunomodulator. This may support the theory of an autoimmune component in the pathogenesis of vitiligo.

 

4. BB-UVB phototherapy

 

Conventional BB-UVB phototherapy utilizes an artificial light source that emits in the radiation spectrum that extends from 280-320 nm (Cui, Shen et al., 1991; Norris, Horikawa et al., 1994). The pilot study of BB-UVB in vitiligo was reported in 1990, and observed that 57% of treated patients had excellent (>75%) repigmentation of vitiligo patches in a 52 week treatment period (Koster W, 1990). The investigators also noted its particular efficacy in facial lesions as well in skin types V and VI (Koster W, 1990). Little definitive evidence purports the use of BB-UVB in vitiligo, primarily due to the dominant and successful use of NB-UVB.

 

BB-UVB with vitamin supplementation was found to be effective in actively spreading vitiligo for inducing repigmentation when given 2-3 times weekly for 6-8 weeks (Don, Iuga et al., 2006). Although the role of vitamin supplementation was not substantiated in the outcome, this particular trial suggests that BB-UVB can be an effective treatment for vitiligo (Don, Iuga et al., 2006). Targeted BB-UVB and MEL were found to have nearly equal rates and degrees of repigmentation when evaluated after 8 treatments (Asawanonda, Kijluakiat et al., 2008).

 

Nearly 60% of patients had 80-100% repigmentation after 70 BB-UVB treatment sessions, a rate comparable to topical PUVA (55.6%) and NB-UVB (54.2%) treated patients in the same trial (El-Mofty, Mostafa et al., 2010). Other studies suggest that BB-UVB is less effective or had no effect compared to PUVA and NB-UVB phototherapy for the treatment of vitiligo (Hartmann, Lurz et al., 2005; Gawkrodger, Ormerod et al., 2008). Furthermore, targeted BB-UVB therapy was found to have limited effectiveness in vitiligo, and treatment-responsive areas were limited to the face (Akar, Tunca et al., 2009).

 

5. NB-UVB phototherapy

 

NB-UVB phototherapy utilizes the 311-313 nm radiation spectrum, which excludes the shorter and more erythmogenic wavelengths of BB- and natural (sunlight) UVB. It has been shown to be more effective than PUVA photochemotherapy, without the adverse side effect profile of psoralen (Table 1) (Bhatnagar, Kanwar et al., 2007; Yones, Palmer et al., 2007). Evidence-based guidelines suggest that NB-UVB should be used instead of PUVA in both adult and pediatric patients who have treatment-resistant disease, widespread involvement (BSA > 10-20%), or disease that severely affects quality of life (Ostovari, Passeron et al., 2004; Gawkrodger, Ormerod et al., 2008; Silverberg, 2010). Furthermore, NB-UVB is suggested as the best choice for generalized disease, with topical immunomodulators (i.e., pimecrolimus cream or tacrolimus ointment) reserved for localized patches (Stinco, Piccirillo et al., 2009). Prognosis is significantly better in those with generalized vitiligo without acral involvement, and reportedly in females (El-Mofty, Mostafa et al., 2010). Less relevant predictors of clinical outcome include skin type, age, and previous response to phototherapy and other vitiligo treatments