Primary cutaneous plasmocytoma C90.0

Mac Intyre, 1850; Kahler, 1889

Rare, primary cutaneous (extramedullary) B-cell NHL lymphoma with a low malignancy grade (see below lymphoma, cutaneous B-cell lymphoma) without (primary detectable) systemic involvement.

Primary plasmacytomas of the skin are very rare.

Secondary (metastatic) manifestations of multiple myeloma are somewhat more common. They usually occur in scarring structures (e.g., sternotomy scars; Li A et al. ) and are associated with a much worse prognosis than primary cutaneous plasmacytomas(Yoo J et al.).

Unknown; extramedullary plasmocytomas are frequently found after organ transplants. Individual reports exist about an EBV association.

The average age is 70 years

Nodular or diffuse tumour cell aggregates in the entire dermis and possibly in subcutaneous fatty tissue. Mostly atypical plasmacytoid cells, mature or immature plasma cells; more rarely immunoblasts. No epidermotropy. Intracellular: immunoglobulins, often monoclonal IgA synthesis and more rarely IgG synthesis. In PAS preparations, PAS-positive inclusions in the cytoplasm (Russel corpuscles).

Immunohistology: Tumor cells are pos. for CD79a, CD38, CD138 and neg. for CD20 and CD45. The analysis of the IgH gene shows mostly monoclonality.

Histological and immunohistological clarification of the findings is important, as well as the exclusion of systemic involvement (extremely accelerated BSG, 1-h value:>100mm n.W., so-called fall reduction, proteinuria with L-chain excretion = (Bence-Jones proteins; Bence-Jones proteins are found in about 60% of all multiple myelomas from IgG or IgA light-chain myeloma). Low-dose CT is recommended as the most sensitive imaging method. Skeletal scintigraphy is less suitable because myeloma foci often do not store data. MRI and PET are suitable for extramedullary foci.

• Clinical differential diagnoses: S. and lymphoma, cutaneous B-cell lymphoma
• Histological differential diagnoses:
• Benign plasma cell proliferations
• cutaneous inflammatory pseudotumor.

The term plasma cytoma is only valid for the solitary monorganic infestation of an organ, in the absence of bone marrow infiltration.

Low-malignant B-cell NHL, as a systemic disease with mostly multilocular or diffuse penetration of the bone marrow by malignant cloned plasma cells, is called"multiple myeloma".

Only in the case of systemic infestation (multiple myeloma) do the following parameters become diagnostically relevant: BSG elevation, paraproteinemia, paraproteinuria (Bence-Jones sample), also cryoglobulins. X-ray skull: mothlike osteolysis (Note: myeloma cells do not have osteolytic activities of their own; however, they stimulate osteolysis by means of various osteoporosis types). Cytokines (RANKL =receptor activator of NF-kB-ligand, MIP-1 = macrophage inflammatory protein = CCL3) stimulate osteoclast and inhibit osteoblast activity. Plasmacellular bone marrow infiltrations, cryoglobulinemia; extremely elevated BSG.

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