Pseudolymphoma of the skin: causes, symptoms, diagnosis, treatment

Pseudolymphomas of the skin are a group of benign lymphoproliferative processes of a reactive nature of a local or disseminated type, which can resolve after removal of the damaging agent or non-aggressive therapy.

B-cell pseudolymphoma (syn.: benign lymphadenosis of Beufverstedt, lymphocytoma of the skin, sarcoidosis of Spiegler-Fendt), is more common in children and adolescents. Clinically, it presents as fairly clearly demarcated, small, pinkish or bluish-red, solitary or (less often) multiple small-nodular elements. Sometimes there are infiltrative-plaque foci with a flat or raised surface, around which small elements are located, as well as solitary nodular foci. The most common localization is the face, auricles, neck, areola of the mammary glands, armpits, scrotum. Sometimes there are symmetrical disseminated miliary nodules on the face and trunk. Changes in the regional lymph nodes and in the peripheral blood may be observed, but the general condition of the patients is good. The development of the disease is associated with the spirochete Borrelia burgdorferi, which penetrates the skin through the bites of ticks - Ixodes ricinus.

Pathomorphology. The epidermis is unchanged, only slightly thickened, under it there is a narrow strip of collagen separating it from the infiltrate. The latter is clearly delimited, located around the vessels and appendages, less often diffuse, occupying the entire dermis, spreading to the subcutaneous tissue. The cellular composition of the infiltrate is rarely monomorphic, in connection with which H. Keri and H. Kresbach (1979) divide lymphocytoma into three types: lymphoreticular, granulomatous and follicular, although they do not deny the existence of mixed types. The main cellular composition is small lymphocytes, centrocytes, lymphoblasts and individual plasma cells. Among them are histiocytes (macrophages), forming the so-called starry sky. Individual histiocytes can be multinucleated, and their cytoplasm can contain phagocytized material (polychrome bodies). Macrophages are clearly visible due to the high content of hydrolytic enzymes in them. Sometimes neutrophilic and eosinophilic granulocytes, as well as tissue basophils, are found in the marginal zone of the infiltrate. In the follicular type, there are pronounced germinal centers that imitate secondary follicles of the lymph node, consisting of a wide lymphocytic ridge and a pale-colored center in which there are mainly centrocytes, histiocytes, centroblasts, sometimes with an admixture of plasma cells and immunoblasts. The clinical manifestation of this disease histologically corresponds mostly to the lymphoreticular and follicular types. The activity of stromal elements in the form of a fibroblastic reaction, new vascular formation, and an increase in the number of tissue basophils are very characteristic of lymphocytoma. In the disseminated form, this picture is more pronounced and the benign nature of the process is more difficult to recognize.

Phenotyping reveals positive B-cell markers (CD19, CD20, CD79a) in the follicular component, where concentrically located chains of dendritic CD21+ cells are also determined. Interfollicular spaces contain CD43+ T-lymphocytes. Reaction with IgM and IgA light chains confirms the polyclonal composition of the infiltrate. Genotyping does not reveal Ig gene rearrangements or intrachromosomal translocation. It is necessary to differentiate B-cell pseudolymphoma from immunocytoma, B-lymphoma from follicular center cells, and MALT-type lymphoma.

T-cell pseudolymphoma (syn.: lymphocytic infiltration of Jessner-Kanof) occurs mainly in adult men, predominantly on the forehead and sides of the face, as well as on the neck, occipital region, trunk and limbs, in the form of individual or multiple foci of a bluish-red or brownish-red color. The disease begins with the appearance of papules, which, increasing due to peripheral growth, form clearly demarcated plaques with a smooth surface. In the central part, as a result of regression of the process, the plaques acquire annular outlines. After several weeks or months, they disappear without a trace, but can reappear in the same or other places. The connection of this disease with chronic lupus erythematosus, not recognized by all, the reaction to light, infection and drugs indicate a reactive nature of the process.

Pathomorphology. The epidermis is mostly unchanged; large, often clearly demarcated infiltrates consisting of histiocytes, plasma cells, and small lymphocytes, which tend to be located around skin appendages and vessels, are noted in the subpapillary and reticular layers of the dermis. No follicles or germinal centers are observed. In the upper parts of the dermis, changes in the collagen substance are found in the form of basophilia, thinning of collagen fiber bundles, proliferation of fibroblasts, and other mesenchymal elements. Phenotyping shows that the predominant pool in the infiltrate is CD43+ T lymphocytes.

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