This is a disorder of unusual expression of CD4+ T cells. Mycosis fungoides is a cutaneous T-cell lymphoma, while Sezary syndrome is a T-cell leukemia, as it is a hematologic neoplasm.
Mycosis fungoides and Sezary syndrome have an average age of onset between 40 and 60 years of age. It is extremely rare for the disease to appear before the age of 20. Often with Sezary syndrome, patients may present in their 60's, having already developed mycosis fungoides earlier in their lives.
In mycosis fungoides, neoplastic CD4+ T-cells infiltrate the skin. Diagnosis is difficult in early phases of disease, as the rashes, plaques and patches resemble eczema or psoriasis.
Patients develop pruritic plaques, patches, and discolored lesions with mycosis fungoides. Early phases of disease often resemble eczema or psoriasis.
Pautrier's abscesses, or microabscesses, are visible under a microscope, and are described as well-defined collections of mononuclear mycosis cells located within the epidermis. These findings are useful in diagnosing mycosis fungoides.
Mycosis fungoides can progress to Sezary syndrome when it infiltrates the bloodstream. This is described as leukemic involvement of malignant T-cells clonally matching those in the skin. Because of this, Sézary disease is sometimes considered a late stage of mycosis fungoides with lymphadenopathy.
On peripheral blood smear, a diagnostic finding in patients with Sezary syndrome are Sezary cells, which are described as having a prominent nuclear cleft. This clefting has lead to the term "cerebriform nuclei" as a description.
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