Clinical history: Skin lesion in a 45 year old woman.
What is the pattern? What is the favored diagnosis and features that suggest it? What immunohistochemistry would be helpful?
Mycosis fungoides is a form of cutaneous T-cell lymphoma. The histological pattern is superficial and perivascular dermatitis, lichenoid, and predominantly lymphocytic. The features that suggest mycosis fungoides as apposed to a non-neoplastic inflammatory lesion are:
epidermotropism (tendency for the lymphocytes to infiltrate into the epidermis)
lymphocytes with a clear perinuclear halo, especially involving lymphocytes within the epidermis
lymphocytes aligned along the basal layer
"fettuccini dermis": the pattern of collagen bundles separated by lymphocytes infiltrating between the bundles
cellular atypia, especially involving lymphocytes within the dermis, including:
cerebriform or hyperconvoluted nuclei
Pautrier's microabscesses: collection of lymphocytes at the epidermal junction or within the epidermis
In early lesions Pautrier's microabscesses may be absent and cellulary atypia may be mild. In addition, many of the lymphocytes present within the lesion represent a physiologic immune reaction and are not neoplastic.
Immunohistochemistry shows positivity for CD3, CD45 and CD4, however rare cases are CD4 negative and CD8 positive. They are CD30 negative, however they may transform into a CD30 positive large cell lymphoma, which carries a worse prognosis. The tumors frequently lack CD7 and Leu-8 expression, however these markers may be positive in tumors. Additionally, inflammatory processes may lose expression of CD7 or Leu-8, but usually not both.