Mycosis fungoides is?
**Core Concept**
Mycosis fungoides is a rare type of cutaneous T-cell lymphoma (CTCL) characterized by the clonal proliferation of malignant T cells in the skin. It is the most common form of CTCL and typically presents with patches, plaques, or tumors on the skin.
**Why the Correct Answer is Right**
Mycosis fungoides is a type of non-Hodgkin lymphoma that involves the skin. The disease is caused by the clonal expansion of malignant T cells, which infiltrate the skin and cause damage to the skin cells. The malignant T cells in mycosis fungoides express CD4, a marker of helper T cells. The disease progresses from patches to plaques and eventually to tumors, which can be painful and bleed easily.
**Why Each Wrong Option is Incorrect**
**Option A:** Mycosis fungoides is also known as Sézary syndrome, which is a more aggressive form of CTCL characterized by the presence of Sézary cells in the blood. While Sézary syndrome is a related condition, it is not the same as mycosis fungoides.
**Option B:** Mycosis fungoides is often confused with pityriasis rosea, a benign skin condition that presents with a similar patchy rash. However, mycosis fungoides is a malignant condition that requires aggressive treatment.
**Option C:** Mycosis fungoides is not caused by a bacterial infection, but rather by the abnormal proliferation of malignant T cells.
**Clinical Pearl / High-Yield Fact**
Mycosis fungoides is often misdiagnosed as a benign skin condition, such as eczema or psoriasis. However, it is essential to consider CTCL in the differential diagnosis of skin lesions, especially in patients with a history of skin cancer or immune system disorders.
**Correct Answer:** C. A type of cutaneous T-cell lymphoma (CTCL).