DIFFERENTIATION AND CLONALITY OF LESIONAL LYMPHOCYTES IN SMALL PLAQUEPARAPSORIASIS

Background: Small plaque parapsoriasis is an idiopathic chronic dermat osis characterized by patches on the trunk and extremities that are of ten smaller than 5 cm in diameter and that sometimes have a digitate c ontour. These latter cases are often referred to as digitate dermatosi s. Histopathologic examination reveals a mild superficial perivascular lymphocytic infiltrate associated with mild spongiosis and parakerato sis. To characterize this disease more completely, we analyzed the dif ferentiation and clonality of lesional lymphocytes using immunohistolo gic and molecular biologic methods. Observations: We studied five case s using a frozen-section immunoperoxidase technique. In each case, the re was a predominantly CD4(+) T-cell infiltrate admired with CD8(+) T cells, Langerhans cells/indeterminate cells, and macrophages. In three cases, the clonality of lesional T cells was studied by denaturing gr adient gel electrophoresis of polymerase chain reaction-amplified T-ce ll receptor-gamma gene rearrangements. Two cases showed a dominant clo nal pattern, while one case exhibited a polyclonal pattern. Clinical f ollow-up disclosed persistent disease in one of the two clonal cases, while lesions in the other clonal case and the polyclonal case gradual ly resolved. Conclusions: Our findings indicate that small plaque para psoriasis is a clinically indolent, histopathologically nonspecific, p redominantly CD4(+) T-cell mediated disease that, at least in some cas es, contains a dominant T-cell clone. These features put small plaque parapsoriasis into a category with certain other members of the paraps oriasis group, namely, pityriasis lichenoides and lymphomatoid papulos is, which have been shown to be clonal T-cell disorders despite their clinically benign course. It remains to be determined if the dominant T-cell clones identified in some cases of small plaque parapsoriasis c an ever be the direct precursors of overt cutaneous T-cell lymphomas.