The value of molecular analysis by PCR in the diagnosis of cutaneous lymphocytic infiltrates

The diagnosis and classification of cutaneous lymphomas remain a challenge for the clinician and dermatopathologist. This diagnostic dilemma is mainly encountered in the distinction between an early malignant lymphoma and a benign reactive lymphocytic infiltrate (pseudolymphoma). Until the beginning of the 1980s, our diagnostic tools were limited to the clinical presentation, course, and histopathology in diagnosis and classification of lymphocytic infiltrates. Advances in immunology and, in particular, in molecular genetics with the introduction of the Southern blot technique and the polymerase chain reaction (PCR) have revolutionized the diagnosis of lymphocytic infiltrates by determination of clonality. In some series, more than 90% of cutaneous T-cell lymphomas have a clonal rearrangement of the T-cell receptor gamma-chain gene, as opposed to very low percentages of rearrangement in T-cell pseudolymphomas. However, the presence of clonality does not necessarily imply malignancy. Cases of pseudolymphomas, lichen planus and pityriasis lichenoides et varioliformis acuta were reported with clonal lymphocytic proliferations. Therefore, care should be exercised in the evaluation of the results of molecular analysis, and these should always be correlated with the clinical, histological and immunophenotypic picture to arrive at the correct diagnosis. It may be expected that the molecular methods for diagnosis of lymphocytic infiltrates will be improved and refined in future, and that sensitivity and specificity will increase.