Pautrier microabscesses

Pautrier microabscesses are small, well-circumscribed clusters of atypical lymphocytes (typically CD4+ helper T-cells) located within the epidermis, often surrounded by a clear halo due to retraction artifact. They are a hallmark histopathologic feature of mycosis fungoides, the most common cutaneous T-cell lymphoma, and its leukemic variant, Sézary syndrome. Pathophysiologically, mycosis fungoides arises from malignant transformation of skin-homing CD4+ T-cells that show epidermotropism—migration into the epidermis without significant spongiosis, distinguishing it from inflammatory dermatoses. The neoplastic cells have characteristic cerebriform (brain-like, convoluted) nuclei visible on histology. Clinically, mycosis fungoides progresses through patch, plaque, and tumor stages, often mimicking eczema or psoriasis early on, making biopsy essential for diagnosis. Pautrier microabscesses are highly specific but only found in a minority of biopsies (varies by stage), so their absence does not rule out the diagnosis. Immunohistochemistry typically shows loss of normal T-cell antigens (e.g., CD7) in the malignant population, aiding diagnosis. Clinical associations include waxing/waning skin patches that can progress to lymphadenopathy and visceral involvement in advanced disease, and when circulating Sézary cells with cerebriform nuclei are seen in peripheral blood, this indicates Sézary syndrome. This is a high-yield board topic given its classic association with CTCL and distinctive microscopic appearance, frequently tested with an image-based question showing epidermal lymphocyte clusters.