Wood lamp is used to diagnose ?
**Core Concept**
The Wood's lamp is a diagnostic tool that utilizes ultraviolet (UV) light to visualize various skin conditions. It works by emitting a specific wavelength of light that interacts with skin pigments, leading to the appearance of characteristic colors.
**Why the Correct Answer is Right**
The Wood's lamp is particularly useful in diagnosing conditions such as vitiligo, where it can highlight areas of depigmentation. This is because the UV light accentuates the contrast between the affected and unaffected skin, making it easier to identify the extent of the condition. The underlying mechanism involves the interaction of UV light with melanin, which is responsible for skin pigmentation.
**Why Each Wrong Option is Incorrect**
**Option A:** Pityriasis versicolor - While the Wood's lamp can help diagnose this condition, it is not its primary use. The correct application of the Wood's lamp involves observing the appearance of yellowish or brownish pigmentation in the affected areas.
**Option B:** Erythema infectiosum - The Wood's lamp is not typically used to diagnose this condition. Other diagnostic methods, such as clinical examination and laboratory tests, are more commonly employed.
**Option C:** Porphyria cutanea tarda - Although the Wood's lamp can be used to diagnose porphyrias, it is not the most specific tool for this condition. Other diagnostic methods, such as urine tests and biopsy, are more commonly used.
**Clinical Pearl / High-Yield Fact**
When using a Wood's lamp, it's essential to note that the skin should be clean and free of any topical medications that may interfere with the results. This is because certain substances can react with the UV light and produce false-positive results.
**Correct Answer: C. Porphyria cutanea tarda**