From the Guidelines
Hypopigmentation patches viewed under a Wood's lamp appear as bright white or blue-white fluorescent areas, indicating conditions where there is a reduction in melanin in the skin. This examination technique helps diagnose several skin disorders including vitiligo, tinea versicolor, and pityriasis alba. According to the guideline for the diagnosis and management of vitiligo 1, Wood’s light is a hand-held ultraviolet (UV) irradiation device that emits UVA, which has been used to identify areas of depigmentation that may not be visible to the naked eye, especially in pale skin.
The mechanism behind Wood's lamp examination is that ultraviolet light (wavelength 320-400 nm) is absorbed by melanin; therefore, areas with decreased melanin reflect more light and appear brighter 1. The pattern, distribution, and specific color of fluorescence help dermatologists differentiate between various hypopigmentation disorders. For accurate results, the examination should be conducted in a completely darkened room after allowing the lamp to warm up for several minutes, with the light held 4-5 inches from the skin surface.
Some key points to consider when using a Wood's lamp for diagnosis include:
- The lamp should be used in a completely darkened room to maximize the visibility of fluorescent areas
- The lamp should be held 4-5 inches from the skin surface to ensure accurate results
- The pattern, distribution, and specific color of fluorescence can help differentiate between various hypopigmentation disorders
- Wood’s light delineates areas of pigment loss, and actively depigmenting areas may appear larger under UV illumination than with visible light 1.
Overall, the Wood's lamp is a valuable non-invasive diagnostic tool for determining the extent of pigmentary disorders that may not be fully visible under normal lighting conditions.
From the Research
Hypopigmentation Patches on Wood's Lamp
The meaning of hypopigmentation patches viewed under a Wood's lamp can be understood through various studies on pityriasis versicolor and its treatment.
- Hypopigmentation patches are a common residual effect after the treatment of pityriasis versicolor, as seen in studies 2, 3, 4.
- The use of a Wood's lamp in diagnosing and monitoring the treatment of pityriasis versicolor is well-established, with the lamp helping to detect the presence of Malassezia furfur, the fungus responsible for the condition 2, 4.
- In the context of hypopigmentation, the Wood's lamp examination can reveal the absence of fluorescence in areas where hypopigmented macules remain after treatment, indicating the eradication of the fungus 2.
- The persistence of hypopigmentation despite successful treatment of the fungal infection suggests that the hypopigmentation may not be directly related to the presence of the fungus, but rather a residual effect of the infection or treatment 5, 4.
Treatment and Hypopigmentation
Different treatments for pityriasis versicolor have been compared in terms of their efficacy and effect on hypopigmentation.
- Ketoconazole and fluconazole have been shown to be effective in treating pityriasis versicolor, with varying effects on hypopigmentation 2, 4, 6.
- Topical tacrolimus has been evaluated as a potential treatment for pityriasis versicolor, with results showing no significant effect on hypopigmentation 5.
- The choice of treatment may depend on various factors, including the severity of the condition, the presence of hypopigmentation, and the potential for relapse 3, 6.