Laboratory Studies
A complete blood cell count with differential should be performed, and a high lymphocyte count or the presence of Sézary cells suggests mycosis fungoides/cutaneous T-cell lymphoma (MF/CTCL).
Procedures
Skin biopsy
Skin biopsy with immunophenotyping analysis and gene rearrangement studies should be performed.
Histologic Findings
Histopathology of small plaque parapsoriasis shows a mild superficial perivascular lymphocytic infiltrate with a nonspecific inflammatory infiltrate of CD4+ and CD8+ T cells. However, CD4+ T cells are predominant. The epidermis may show mild spongiosis, focal hyperkeratosis, scale crust, parakeratosis, and occasional exocytosis. Often, the pattern is not diagnostic and is nonspecific. Lymphocytes are small and do not show atypical features.
In large plaque parapsoriasis, a superficial dermal inflammatory infiltrate consists predominantly of lymphocytes. Numerous lymphocytes abut the dermal-epidermal junction and single lymphocytes can be observed in the epidermis. Lymphocytes are generally small and do not show atypical nuclei. Blood vessels are dilated, and melanophages can be present. The epidermis shows flattening of the rete ridges when epidermal atrophy is prominent on clinical examination. Acanthosis of the epidermis and irregular hyperkeratosis of the cornified layer are present. In contrast to small plaque parapsoriasis, spongiosis is absent.
Gene rearrangement studies can assist in excluding MF or CTCL.
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Small plaque parapsoriasis.
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Small plaque parapsoriasis.
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Large plaque parapsoriasis.
