**Core Concept**
Mycosis fungoides is a rare type of cutaneous T-cell lymphoma characterized by the malignant proliferation of T-lymphocytes in the skin. It is the most common form of primary cutaneous lymphoma, often presenting with skin lesions that progress to advanced stages.

**Why the Correct Answer is Right**
Mycosis fungoides involves the clonal expansion of malignant T-lymphocytes, which infiltrate the skin and cause various skin manifestations. The disease progresses through four stages: patch, plaque, tumor, and erythroderma. The malignant T-lymphocytes in mycosis fungoides typically express CD4, a marker of helper T-cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Mycosis fungoides does not primarily affect the lymph nodes, which are more commonly involved in other types of lymphomas.
**Option B:** Mycosis fungoides is not caused by a viral infection, unlike some other types of lymphomas.
**Option C:** Mycosis fungoides does not typically present with systemic symptoms such as fever or weight loss, which are more characteristic of advanced lymphomas.

**Clinical Pearl / High-Yield Fact**
Mycosis fungoides often presents with skin lesions that resemble eczema or psoriasis, making it challenging to diagnose, especially in early stages. A high index of suspicion and proper skin biopsy are essential for accurate diagnosis.

**Correct Answer: C. Sézary syndrome is not a correct answer, however, mycosis fungoides is a type of cutaneous T-cell lymphoma and is characterized by the malignant proliferation of T-lymphocytes in the skin.**