**Core Concept**
Erythroderma, also known as exfoliative dermatitis, is a condition characterized by widespread scaling, erythema, and peeling of the skin, often involving more than 90% of the body surface. It can be caused by various underlying dermatological conditions. **Psoriasis** is one such condition that can lead to erythroderma.

**Why the Correct Answer is Right**
**Psoriasis** is a chronic skin condition that can progress to erythroderma in severe cases. The exact mechanism involves an abnormal immune response, keratinocyte proliferation, and the release of pro-inflammatory cytokines. This leads to the characteristic scaling and erythema seen in psoriatic erythroderma.

**Why Each Wrong Option is Incorrect**
**Option A:** Pityriasis alba is a mild, superficial dermatitis that does not typically progress to erythroderma.
**Option B:** Pityriasis versicolor is a fungal infection that causes localized hyperpigmentation, not erythroderma.
**Option D:** Lichen planus can cause widespread skin lesions, but it is less commonly associated with erythroderma compared to psoriasis.
**Option E:** Eczema, or atopic dermatitis, can cause severe skin inflammation but is less likely to cause erythroderma compared to psoriasis.

**Clinical Pearl / High-Yield Fact**
Remember that psoriasis is a common cause of erythroderma, and its treatment requires aggressive management of the underlying condition.

**Correct Answer:** C. Psoriasis