Value of PCR detection of TCR gamma gene rearrangement in the diagnosis of cutaneous lymphocytic infiltrates.

In this study, we analyzed the reliability and usefulness of the polymerase chain reaction (PCR) for the detection of T-cell receptor (TCR)gamma gene monoclonal rearrangement. We first tested for the specificity and sensitivity of this strategy, against the classical criteria of Southern blot analysis (SBA). Of the 27 samples tested, results agreed in all but two. Broader analysis of these cases demonstrated the high specificity (absence of false positives) of the PCR strategy, together with its limited sensitivity (10% of false negatives). The usefulness of this PCR approach was then tested on a panel of 28 biopsy specimens of cutaneous lymphocytic infiltrates. Monoclonal TCR gamma rearrangement was detected in seven of eight cases of early stage mycosis fungoides (MF), one of two Sezary syndrome (SS) cases, two of two non-MF T-cell lymphoma, and two of three lymphomatoid papulosis. Monoclonality was not detected in any of the 11 benign cases (parapsoriasis and inflammatory dermatosis). Results obtained with this new molecular strategy provide additional support for the hypothesis of a monoclonal origin for most early stage T-cell MF. They also suggest the heterogeneous nature of some lymphomatoid papulosis lesions. Therefore, due to the difficulty in detecting T-cell monoclonality by immunohistochemical techniques, PCR can be a useful alternative strategy to SBA. It could also be used as a complementary technique in the routine diagnosis of T-cell cutaneous infiltrates.