Psoralen – A is used in the treatment of :
**Core Concept**
Psoralens are a class of synthetic compounds that are used in the treatment of certain skin disorders. They work by absorbing ultraviolet (UV) light, which leads to the formation of covalent bonds between the psoralen and DNA, thereby inhibiting DNA synthesis and cell division. This mechanism is particularly useful in the treatment of skin conditions that involve excessive cell proliferation, such as psoriasis.
**Why the Correct Answer is Right**
The correct answer is **C. Psoriasis**. Psoriasis is a chronic autoimmune skin condition characterized by thickened, scaly skin patches due to abnormal cell proliferation. Psoralen, in combination with UVA light (PUVA therapy), is a well-established treatment for moderate to severe psoriasis. Psoralen's ability to inhibit DNA synthesis and cell division makes it an effective treatment for this condition.
**Why Each Wrong Option is Incorrect**
**Option A:** Vitiligo is a condition characterized by loss of skin pigment, not excessive cell proliferation, so psoralen would not be an effective treatment.
**Option B:** Acne is a skin condition that involves inflammation and comedone formation, not excessive cell proliferation, so psoralen would not be a suitable treatment.
**Option D:** Skin cancer involves uncontrolled cell growth, but psoralen's mechanism of action is not directed against cancer cells, so it would not be an effective treatment for skin cancer.
**Clinical Pearl / High-Yield Fact**
Psoralen is often used in combination with UVA light (PUVA therapy) to enhance its effectiveness in treating psoriasis. This combination therapy has been shown to be more effective than either treatment alone.
**Correct Answer:** C. Psoriasis.