**Core Concept**
Psoriasis vulgaris is a chronic autoimmune skin condition characterized by abnormal proliferation of keratinocytes, leading to the formation of erythematous scaly plaques. The exact pathogenesis involves an interplay between genetic predisposition, immune system dysregulation, and environmental triggers.

**Why the Correct Answer is Right**
The patient's presentation of erythematous scaly plaques over a long duration, occasional itching, and exacerbation during winters is suggestive of psoriasis vulgaris. This condition is often associated with an imbalance of the immune system, particularly the involvement of T cells and the release of pro-inflammatory cytokines. The increased proliferation of keratinocytes in the epidermis is mediated by the activation of various signaling pathways, including the NF-κB pathway. Additionally, the presence of remission and relapse in the patient's history further supports the diagnosis of psoriasis vulgaris, as this condition is known for its unpredictable course.

**Why Each Wrong Option is Incorrect**
**Option A:** Lichen planus is characterized by purplish, itchy, flat bumps, which is not consistent with the patient's presentation of erythematous scaly plaques.
**Option C:** Pityriasis rosea typically presents with a herald patch followed by a widespread eruption of oval-shaped scaly patches, which does not match the patient's long-standing history of lesions.
**Option D:** Seborrhic dermatitis is characterized by yellowish, oily, scaly patches, primarily affecting the scalp, face, and torso, which does not align with the patient's presentation.

**Clinical Pearl / High-Yield Fact**
Psoriasis vulgaris is often associated with other systemic comorbidities, such as psoriatic arthritis, and may have a genetic predisposition, particularly in individuals with a family history of the condition. Early recognition and treatment can significantly improve the patient's quality of life.

**✓ Correct Answer: B. Psoriasis vulgaris**