Differential diagnosis between T-cell lymphoma and Hodgkin's disease: the value of mitotic counts and pericapsular infiltration.

The distinction between peripheral T-cell lymphoma (PTCL) and Hodgkin's disease (HD), particularly HD of the mixed cellularity subtype (HDMC), can be difficult at times using current morphologic criteria. This study assessed the value of using mitotic activity and pericapsular invasion in discriminating between the two diseases. Mitotic activity was evaluated in 64 cases of HDNS (nodular sclerosis), 51 of HDMC, 14 of HDLP (lymphocyte predominant), 7 of HDLD (lymphocyte depleted), and 28 cases of PTCL. The number of mitoses in random high-power fields (hpf) was counted independently by two observers. Interobserver agreement on mitotic counts was achieved with a 0.97 coefficient of correlation. Statistical analyses demonstrated significant differences in mitotic counts between HD and PTCL (p less than 0.01), but not within the subtypes of HD. A value of greater than 20 mitoses/20 hpf was obtained in only 10% of HD, in contrast to 70% of PTCL. The mitotic rate was greater than 40/20 hpf in 43% of PTCL, but in no case of HD. In addition, perinodal extension of disease was a significant differentiating feature between PTCL and HD, especially HDMC (p less than 0.001). There was also a significant difference in the age distribution between patients in the two disease groups, with PTCL being seen more frequently in the older age group. The results of this study confirm that counting of mitoses is reproducible, and that mitotic activity and the presence of pericapsular disease are two additional morphologic criteria that are helpful in making the distinction between HD and PTCL.