Mycosis fungoides is best described as
**Core Concept**
Mycosis fungoides is a rare type of cutaneous T-cell lymphoma characterized by the clonal proliferation of malignant T cells in the skin. It is the most common form of primary cutaneous lymphoma.
**Why the Correct Answer is Right**
Mycosis fungoides is a chronic, insidious disease that often presents with patches, plaques, or tumors on the skin. The malignant T cells in mycosis fungoides are typically CD4+ helper T cells that express the skin-homing receptor CCR4 and the T-cell receptor (TCR) alpha/beta. These cells accumulate in the skin due to the expression of specific chemokines and adhesion molecules.
**Why Each Wrong Option is Incorrect**
**Option A:** Sézary syndrome is a more aggressive variant of mycosis fungoides characterized by the presence of Sézary cells in the blood. It is not the best description of mycosis fungoides itself.
**Option B:** Psoriasis is a chronic inflammatory skin disease characterized by the accumulation of keratinocytes and T cells in the epidermis, but it is not a type of lymphoma.
**Option C:** Mycosis fungoides is not a fungal infection, but rather a type of cancer.
**Clinical Pearl / High-Yield Fact**
Mycosis fungoides often presents with a characteristic "bathing trunk" distribution of skin lesions, which is a clue to its diagnosis.
**Correct Answer:** C. Mycosis fungoides is not a fungal infection, but rather a type of cancer.