Demonstration of frequent occurrence of clonal T cells in the peripheral blood but not in the skin of patients with small plaque parapsoriasis

Clinical, immunohistological, and molecular biological data suggest the chr onic dermatosis small plaque parapsoriasis (SPP) to be a precursor of mycos is fungoides (MF), However, most data are contradictory and confusing due t o inexact definition of SPP. Recently, clonal T cells were detected in skin and blood samples of early MF. Because demonstration of identical T-cell c lones in skin and blood of SPP patients would indicate a close relationship of SPP to MF, we investigated the clonality of skin and blood specimens fr om 14 well-defined SPP patients. By a polymerase chain reaction (PCR) ampli fying T-cell receptor gamma rearrangements and subsequent high-resolution e lectrophoresis, clonal T cells were detected in 9 of 14 initial and 32 of 4 9 follow-up blood samples, but in 0 of 14 initial skin specimens. Even a do ne-specific PCR showing the persistence of the initial blood T-cell clone i n 20 of 20 follow-up samples, failed to detect the T-cell clone in the skin . In 2 patients, the clonal T cells were shown to be CD4(+). For the first time, the majority of SPP patients was shown to carry a T-cell clone in the peripheral blood. Although a relation between circulating clonal i cells a nd SPP cannot directly be proven by the applied techniques, our results ind icate blood T-cell clonality to be a characteristic feature of SPP and CTCL because analysis of multiple controls and clinical workup of our SPP patie nts excluded other factors simulating or causing a clonal T-cell proliferat ion. A sufficient cutaneous antitumor response but also an extracutaneous o rigin of the T-cell clones might explain the failure to detect skin infiltr ating clonal T cells. (C) 1999 by The American Society of Hematology.