Introduction to Wood's Lamp Examination
Wood's lamp examination is a valuable diagnostic tool in the field of
infectious diseases. Utilizing ultraviolet (UV) light, this non-invasive method is commonly employed to detect certain fungal and bacterial infections, as well as other dermatological conditions. The examination is named after Robert Williams Wood, who developed the Wood's lamp in 1903.
How Does the Wood's Lamp Work?
The Wood's lamp emits UV light at a wavelength of approximately 365 nanometers. When directed at the skin, it causes certain substances to fluoresce, or glow. This fluorescence is typically invisible to the naked eye under normal light but becomes apparent under UV illumination. Different infections and dermatological conditions can produce characteristic colors when exposed to the Wood's lamp.
What Infections Can Be Diagnosed with Wood's Lamp?
The Wood's lamp is particularly useful in diagnosing specific
fungal infections such as tinea capitis. Some strains of
Microsporum fungi fluoresce green under UV light, helping to differentiate them from other non-fluorescing dermatophytes. Additionally, it can help identify bacterial infections like
erythrasma, caused by
Corynebacterium minutissimum, which displays a coral-red fluorescence.
Are There Limitations to Wood's Lamp Examination?
While the Wood's lamp is a useful tool, it has limitations. Not all fungal and bacterial infections fluoresce under UV light, which means a negative result does not rule out infection. For instance,
Candida infections do not typically fluoresce. Moreover, the presence of certain substances such as soap, lotions, or fabric fibers on the skin can affect fluorescence, leading to false positives or negatives.
What Other Conditions Can Be Detected?
Beyond infectious diseases, Wood's lamp examination can help diagnose various
dermatological conditions. It is used to identify pigmentation disorders like
vitiligo, which appears as a bright white or blue-white fluorescence. It can also be used to detect conditions such as
porphyria and
pityriasis versicolor, which may show specific fluorescence patterns.
Preparation and Procedure
To prepare for a Wood's lamp examination, patients should avoid applying lotions, creams, or cosmetics to the area to be examined, as these can interfere with the results. During the procedure, the clinician will darken the examination room and hold the Wood's lamp approximately four to five inches from the skin. The resulting fluorescence, if any, will be observed and analyzed.
Interpreting the Results
Interpreting Wood's lamp results requires expertise and understanding of the fluorescence patterns associated with different conditions. For instance, a bright apple-green fluorescence might indicate a
tinea capitis infection caused by
Microsporum canis. In contrast, a coral-red fluorescence suggests erythrasma. It is important to correlate these findings with clinical symptoms and, if necessary, confirm the diagnosis with additional tests.
Conclusion
In the realm of infectious diseases and dermatology, Wood's lamp examination is a quick, non-invasive, and cost-effective diagnostic tool. While it is not definitive for all infections, it provides valuable insights that can guide further testing and treatment. Understanding its applications and limitations enhances its utility in clinical practice.
