The role of immunohistochemical analysis in the diagnosis of parapsoriasis.

Parapsoriasis is a chronic dermatosis whose biological distinction from early mycosis fungoides, the most frequent form of cutaneous T-cell lymphoma, is still not clearly defined. Two types of parapsoriasis have been delineated: large-plaque parapsoriasis and small-plaque parapsoriasis. The lack of clinical and histological features, which may allow distinguishing parapsoriasis from early mycosis fungoides has prompted several investigations to assess the role of immunohistochemistry in establishing a conclusive diagnosis of these conditions. However, the additional data obtained by immunohistochemical analysis concerning the CD4/CD8 ratio, the aberrant expression of T-cell antigens and the expression of proliferation markers has not generally helped establish a more definitive diagnosis. This review critically discusses these immunohistochemical markers and their use in diagnosis of parapsoriasis.