**Core Concept**
Mycosis fungoides is a rare form of cutaneous T-cell lymphoma characterized by the malignant transformation of T-lymphocytes in the skin. It is also known as Sézary syndrome when it involves the blood.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology and clinical presentation of mycosis fungoides. This disease is primarily a skin disorder, and its progression can be slow. It often presents with patches, plaques, or tumors on the skin, which can be erythematous or hyperpigmented. The disease can progress to involve lymph nodes and internal organs, but it typically starts in the skin.

**Why Each Wrong Option is Incorrect**
**Option A:**
- Not a characteristic of mycosis fungoides, which is a T-cell lymphoma.

**Option B:**
- True, mycosis fungoides is a type of cutaneous T-cell lymphoma.

**Option C:**
- This is a characteristic of mycosis fungoides, which often presents with skin patches and plaques.

**Option D:**
- Not a typical feature of mycosis fungoides, which usually starts in the skin and can progress to lymph nodes and internal organs.

**Clinical Pearl / High-Yield Fact**
Mycosis fungoides is the most common form of cutaneous T-cell lymphoma, and it often presents with skin patches or plaques that can be mistaken for eczema or psoriasis.

**Correct Answer:** D.