Approach to lymphoproliferative infiltrates of the skin. The difficult lesions.

Primary cutaneous lymphomas (CLs) are the second most common group of extranodal non-Hodgkin's lymphomas. Cutaneous T-cell lymphomas (CTCLs) account for 60% to 65% of all primary CLs, whereas 20% to 25% of CLs are of B-cell origin. Besides the most common and well-known forms of CL, such as mycosis fungoides and follicular B-cell lymphomas, there are some rare and unusual variants of CL that represent about 10% of lymphoproliferative skin infiltrates. Discussed in detail are T- and B-cell pseudolymphomas as simulators of CL, the group of parapsoriasis and early mycosis fungoides, circumscribed CTCL, such as pagetoid reticulosis and syringolymphoid hyperplasia, granulomatous variants of CTCL, the group of primary CD30+ CTCL and the controversies in the classification and some rare, but distinct cutaneous B-cell lymphomas. The final diagnosis in CL is based on a constellation of clinical, histopathologic, and molecular-biologic criteria.