|
| Fig. 3.2 Wood’s light examination of the groin area demonstrating classic coral red fluorescence associated with erythrasma. (Courtesy of John L. Aeling, MD.) |
|
| Fig. 3.3 Wood’s light examination of the urine in a patient with porphyria cutanea tarda demonstrating classic coral red fluorescence with normal urine specimen exhibited for comparison. (Courtesy of James E. Fitzpatrick, MD.) |
A Wood’s light produces invisible long-wave ultraviolet radiation, or “black light,” at a wavelength of 360 nm. When this light strikes the surface of the skin or urine, fluorescence is produced in some disorders. This fluorescence is best observed in a completely dark room. The Wood’s lamp is useful in diagnosing cases of several skin conditions: tinea capitis (see preceding text), tinea versicolor (dull yellow fluorescence), erythrasma (coral red fluorescence; Fig. 3-2), and
Pseudomonas infections of the skin (green fluorescence). It is also useful as a screening test in porphyria cutanea tarda as the urine fluoresces a coral red color (Fig. 3-3). The Wood’s light may also be used in certain disorders of pigmentation. In patients with hyperpigmentation, it is used to localize the site of the pigment because it accentuates superficial epidermal pigment, whereas deeper dermal pigment is unchanged. It is also used in patients with vitiligo because it demonstrates complete depigmentation. Finally, it can be used to delineate the borders of melanocytic lesions, such as lentigo maligna, prior to surgery.
