Epidermotropic B-Cell Lymphoma

The patient is an 89 y/o male who presented with an explosive onset of a generalized skin rash that clinically resembled pityriasis rosea. The rash differs from classic pityriasis rosea as a number of the lesions were fairly infiltrative plaques and as well there was a plum-colored nodule in the wrist area. The patient otherwise feels well.

This distinctive clinical presentation along with the histomorphology and phenotypic profile is diagnostic of a very rare form of B-cell lymphoma consistent with so-called epidermotropic B cell lymphoma. In fact the epidermotropic properties are present on all three biopsies but are best exemplified by the original biopsy where an interesting pattern of neoplastic B-cells colonizing the basal layer of the epidermis is observed. As with other cases of epidermotropic B-cell lymphoma the cell of origin does not appear to be of follicle center derivation based on the lack of staining for CD10 and BCL6 on our repeat stain. The neoplastic B cells express an activated phenotype in that they are bcl-2 and MUM-1 positive and also express IgG. It has been postulated that this form of B-cell lymphoma is of marginal zone derivation and indeed the phenotypic profile would be consistent with this construction

Large cell transformation is a feature of this particular case. We have encountered large cell transformation in the past in epidermotropic marginal zone lymphoma. A very unique feature of this case is the angioinvasive and perineural invasion in a fashion somewhat reminiscent of the type of angiotropic B-cell lymphomas that occur in the setting of lymphomatoid granulomatosis.

The concept of epidermotropic B cell lymphoma as a distinct form of B-cell neoplasia is an emerging one. There is almost exclusive involvement in older men presenting with a distinctive pityriasis rosea-like rash. These patients are often times otherwise asymptomatic although investigations frequently do disclose splenic involvement as well as bone marrow involvement. The clinical course is one that does respond very well to chemotherapeutic intervention with an overall excellent prognosis despite clinical and h stomorphologic features that could be indicative of a more aggressive clinical course (i.e., the degree of angioinvasion and large cell transformation).

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Slide 1: At low power, one can appreciate the atypical, extensive lymphocytic infiltrate.

Slide 2: There is a component of interface change whereby lymphocytes are present along the dermal-epidermal junction with concomitant vacuous alteration of the basal layer keratinocytes with attendant epidermal attenuation alternating with zones of psoriasiform hyperplasia accompanied by slight hyperkeratosis. The papillary dermis is somewhat edematous. The lymphocytes that are permeative of the epidermis to define this vacuous interface process are small to intermediate in size showing rounded to somewhat angulated nuclear contours with nuclear hyperchromasia.

Slide 3: There is an extensive dermal infiltrate which assumes a very orderly arrangement around blood vessels, nerves and the eccrine coil. There is some component of interstitial infiltration as well. This infiltrate is very atypical and far exceeds the degree of intraepidermal lymphoid atypia recognizing that there is likely a histomorphologic spectrum of this abnormal lymphoid process ranging from the smaller lymphocytes that prevail in the epidermis to the larger ones found in the dermis. Within the dermis there are many lymphocytes that are in the 15-20 micron size range.

Slide 4: In analyzing the CD3 positive T cell component and comparing it to the CD20 positive B cell populace (see next photo) the overall T to B cell ratio is in the 1:1 realm.

Slide 5: Of note, is the fact that the CD20 preparation does highlight B lymphocytes within the epidermis demonstrating that the lymphocytes that colonize the basal layer of the epidermis in fact are of B cell lineage with a similar epitheliotropic B cell populace noted within the outer root sheath epithelium of the hair follicle. In addition, the very large atypical lymphocytes that prevail within the dermis are highlighted by CD20.

Slide 6: The Ki-67 proliferation index is higher in the areas of larger cell infiltration with an overall percentage in the 30% realm.

Slide 7: 20% or so of the infiltrate shows nuclear staining for c-Myc.