Pattern of distribution and intensity of lymphoblastogenesis as an aid to distinguishing pseudolymphomas from lymphomas

SUMMARY Pseudotymphomas and malignant lymphomas may be distinguished on the basis of their protiferative activities, evaluated by radioautography after incorporation of tritiated thymidine. In malignant lymphomas, cells synthesizing DNA are numerous and are distributed regularly in the infiltrate. In pseudolymphomas many atypical cells do not synthesize DNA, and those labelled with [ 3 H]TdR arc often grouped in restricted areas of the infiltrate. Ideally, the term pseudolymphoma refers to a pathological process that histologically resembles malignant lymphoma but behaves in a benign fashion. A common feature which suggests a pseudolymphoma is the presence of a dense infiltrate containing atypical lymphocytoid cells, a number of which are in mitosis. In the last decade a number of distinct types of pseudolymphomas have been more clearly identified (Connors & Ackerman, 1976, 1979; Barr, Schneidman & Graham, 1978; Macaulay, 1978). Unfortunately, some lesions which appeared to be pseudolymphomas, particularly lymphomatoid papulosis, have antedated, and in some instances have been coincident with, the development of malignant lymphoma (Kawada el al ., 1969; Black & Wilson Jones, 1972; Dupont, 1973; Fine, Meltzer & Rudner, 1974; Macaulay, 1978; Pcrrot et al ., 1978; Messenger, Marshall & Summerly, 1981; Schecn, Doyle & Winkelmann 1981; Weinman & Ackerman, 1981). Conversely, some lesions with apparently unequivocal histological features of malignant lymphoma have been known to resolve uneventfully. Despite much effort, the usual conclusion is that there is no definable histological difference between some cutaneous pseudolymphomas that occur in patients who develop malignant lymphoma and in those who do not. Furthermore the boundaries between inflammatory reactions and pseudolymphomas or lymphomas are not yet established (Black, 1982; Thiers, 1982).