**Question:** Drug of choice for treatment of psoriasis involving <10% of BSA (body surface area) is A. Methotrexate B. Corticosteroids C. Calcipotriol D. Coal Tar **Correct Answer:** D. Coal Tar **Core Concept:** Psoriasis is a chronic, immune-mediated inflammatory skin disorder characterized by excessive keratinocyte proliferation, leading to the formation of red, scaly plaques. Treatment options depend on the extent of skin involvement. For lesions involving <10% of body surface area (BSA), topical treatments are usually preferred over systemic ones due to their lower risk profile. **Why the Correct Answer is Right:** Coal Tar (PTU) is a topical treatment commonly used in the management of mild to moderate psoriasis involving <10% BSA, as it has anti-inflammatory, antiproliferative, and immunomodulatory effects. PTU reduces the rate of keratinocyte proliferation and decreases the production of inflammatory cytokines. This makes it an effective option for small, localized areas where the risk of systemic side effects from systemic medications is higher. **Why Each Wrong Option is Incorrect:** A. Methotrexate (MTX): MTX is a systemic antifolate used for severe psoriasis, not mild to moderate cases involving <10% BSA. Its systemic effects and potential toxicity make it unsuitable for localized lesions. B. Corticosteroids: Topical corticosteroids are used for inflammatory skin conditions, but they are not indicated for psoriasis due to their limited anti-psoriatic effects and higher risk of side effects, particularly in localized areas. C. Calcipotriol: Calcipotriol is a Vitamin D analog used for psoriasis, but it is less potent than coal tar. While it is effective for mild to moderate plaque psoriasis, it is not the first choice for small localized lesions involving <10% BSA due to its less potent anti-psoriatic effects compared to coal tar. **Clinical Pearl:** Psoriasis treatment selection depends on the extent of involvement. For localized, mild to moderate cases involving <10% BSA, coal tar remains a suitable first-line treatment option due to its anti-inflammatory, antiproliferative, and immunomodulatory effects, as well as its lower risk profile compared to systemic agents. This ensures effective treatment while minimizing potential side effects.