**Question:** DOC of pustular psoriasis

**Core Concept:** Psoriasis is a chronic inflammatory skin disorder classified into various types, including plaque, guttate, inverted, erythrodermic, and pustular psoriasis. Pustular psoriasis is characterized by the formation of sterile pustules without infection.

**Why the Correct Answer is Right:** The correct answer is D - Methotrexate. Methotrexate is an immunosuppressive drug that primarily targets the immune system by inhibiting the enzyme dihydrofolate reductase, which is crucial for purine and pyrimidine synthesis. In the context of pustular psoriasis, methotrexate works by suppressing the overactive immune response involved in the pathogenesis of this condition.

**Why Each Wrong Option is Incorrect:**

A. **Option A - Acitretin:** Acitretin is a retinoid (derivative of vitamin A) that primarily acts as a modulator of keratinocyte differentiation and is effective in treating psoriasis vulgaris (plaque psoriasis). It is not effective in the management of pustular psoriasis due to its mechanism of action not addressing the underlying immune dysregulation in pustular psoriasis.

B. **Option B - Corticosteroids:** Corticosteroids are immunosuppressive drugs that work by suppressing the inflammatory response and reducing the release of pro-inflammatory cytokines. Although corticosteroids can be used in psoriasis management, they are not specific for pustular psoriasis and may not address the primary immune dysregulation involved in the pathogenesis of pustular psoriasis.

C. **Option C - Phototherapy:** Phototherapy, including UVB and PUVA, is a treatment modality for psoriasis involving exposure to ultraviolet radiation or psoralen (a photosensitizing drug) to modulate keratinocyte proliferation and inflammation. Phototherapy is not specific to pustular psoriasis and may not address the primary immune dysregulation involved in the pathogenesis of pustular psoriasis.

D. **Option D - Methotrexate:** As mentioned earlier, methotrexate is an immunosuppressive drug that targets the immune system, specifically interfering with the DNA synthesis and cell division, which is crucial in the management of pustular psoriasis due to its ability to address the underlying immune dysregulation in pustular psoriasis.

**Core Concept:** Psoriasis is a chronic inflammatory skin disorder characterized by keratinocyte proliferation and immune dysregulation. Pustular psoriasis is a subtype of psoriasis that presents with sterile pustules. Methotrexate is the correct answer because it modulates the immune system, which addresses the primary immune dysregulation involved in pustular psoriasis.

**Why Core Concept Matters:** Understanding the core concept of psoriasis as a disorder involving immune dysregulation and keratinocyte proliferation is essential for distinguishing between various subtypes of psoriasis and selecting the appropriate treatment options. The correct treatment for pustular psoriasis is methotrexate due to its immunosuppressive properties, which are crucial