Ultraviolet B Phototherapy

Key points

Phototherapy with UV light can be used in the treatment of several cutaneous disorders.
Phototherapy is an efficacious treatment option in the management of psoriasis and should be a first therapy considered in patients with moderate-to-severe plaque psoriasis.
Narrowband UV-B is used as the first-line phototherapy treatment option for moderate-to-severe psoriasis due to its clinical efficacy and mild side-effect profile.
Targeted UV-B therapy phototherapy and employment of excimer lasers are excellent options for patients with more limited disease, although there are now reports of use for extensive disease.

Introduction

Definition

Phototherapy refers to the use of nonionizing radiation, from the UV range, in the treatment of skin disorders ( Table 2.1 ). It represents an efficacious, cost-effective, and generally nonimmunosuppressive staple in the management of psoriasis.

Table 2.1

Ultraviolet radiation spectrum

UV Spectrum (10–400 nm)
Abbreviation	Wavelength (nm)
UV-A	320–400
UV-B	290–320
UV-C	200–290

History

The use of sunlight in the treatment of cutaneous diseases can be traced back to ancient times. Evidence dating thousands of years demonstrates the use of plant extracts, including those from the Ammi majus plant (psoralens), followed by sun exposure to treat vitiligo in Egypt and India. However, it was not until the late nineteenth century that heralded major advances in the development and use of phototherapy. In 1901, Niels Ryberg Finsen published the results of the treatment of lupus vulgaris with a carbon arc lamp, which marked a breakthrough in the treatment of skin diseases. For this, Finsen received a Nobel Prize in medicine, the first and only one ever awarded in the field of dermatology.

Shortly after in 1925, William Goeckerman combined the use of UV radiation with coal tar in the treatment of psoriasis. The Goeckerman regimen as it came to be known would remain a mainstay in phototherapy treatment of psoriasis for several decades. A major shortcoming of the Goeckerman regimen was the low output of the lamps. However, in 1978, Wiskemann introduced broadband UV-B radiation in a closed chamber to treat psoriasis, which mitigated this drawback. Despite these advances, broadband UV-B radiation was less efficacious than psoralens followed by UV-A radiation, also known as PUVA therapy, and as a result, did not gain widespread popularity. It was not until the late 1970s when Parrish and Jaenicke determined the action spectrum of psoriasis with a peak response at 313 nm that gave impetus to narrowband (NB) UV-B as a new phototherapeutic modality. In 1988, both Van Weelden and colleagues and Green and colleagues demonstrated the superior clinical efficacy of NB UV-B and subsequently marked the decline of broadband-UV-B (BB-UV-B) use for psoriasis.

Types

This chapter provides an overview of UVB phototherapy in the management of psoriasis.

Broadband ultraviolet B (290–320 nm)

Broadband (BB) UV-B phototherapy was initially described in the Goeckerman regimen in 1925. For many decades, BB-UV-B remained an option in the psoriasis treatment arsenal despite being less efficacious than other treatment modalities. Presently, however, BB-UV-B has largely been replaced by NB-UV-B radiation, which has demonstrated superior efficacy in clearing psoriatic lesions.

Narrowband ultraviolet B (311–313 nm)

First defined in 1976, NB-UV-B has taken the place of BB-UV-B in the treatment and management of psoriasis. NB-UV-B has gained popularity over PUVA in the treatment of psoriasis for several reasons. First, NB-UV-B had similar efficacy rates compared with PUVA. Therefore, NB-UV-B is generally favored over PUVA due to greater ease of use for the patient. Another factor is the increased risk of squamous cell cancer (SCC) associated with PUVA treatments. The risk of SCC increases as the number of PUVA treatments increases. NB-UV-B phototherapy has not been shown to incur any increased risk of skin cancer. Last, NB-UV-B is safe to use in children and pregnant patients and lacks psoralen-related side effects, which ultimately makes it more favorable as an initial phototherapy modality.

Targeted phototherapy

Targeted phototherapy is a method of phototherapy in which only affected areas of skin are treated. Various devices can be used to deliver focused UV-B radiation on skin lesions while sparing uninvolved skin. These devices include high fluence devices, like the excimer laser and flash lamp, and lower output devices, like UV-B light-emitting diodes. Introduced in 1997, the 308-nm excimer laser contains an unstable mixture of xenon and chloride, which form “excited dimmers.” It is the dissociation of these dimers that produces the monochromatic wavelength, which is transmitted via a fiber-optic cable to the lesion. The excimer laser allows for targeted therapy that spares uninvolved skin, especially in areas that are otherwise difficult to treat, like the scalp, hands, and feet. In addition, it can generate high fluencies of UV-B, resulting in faster clearing and fewer exposures. Although the excimer laser is not suitable for large body surface areas because the treatment may be considerably resource intensive and lengthy, the availability of more powerful UV emitting devices (and aggressive treatment protocol) is extending the range of area that can be treated. Although targeted treatment has generally been used for mild, localized psoriasis, it can also be used for severe psoriasis of the palms/soles or even for extensive disease.

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