A 62-year-old man presented with asymptomatic skin lesions that were located exclusively on the thorax and had appeared more than 15 years earlier. The patient had no relevant medical or surgical history and was not taking regular medication. Physical examination revealed erythematous-brownish plaques without scaling or infiltration (Fig. 1A). The palms of the hands, soles of the feet, and the mucous membranes were free of any lesions. Darier sign was negative and neither lymphadenopathy nor organomegaly were evident on palpation.

Figure 1.

Clinical image. Erythematous and brown papules on both sides of the patient’s trunk.

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Although clinically the patient’s lesions could be considered compatible with mastocytosis, the duration of the lesions and the absence of Darier sign were striking. The clinical stability of the lesions over several years and the absence of palmoplantar involvement decreased the likelihood of secondary syphilis.

Results of laboratory tests revealed a normal biochemical profile and a normal complete blood count. The only findings of interest were polyclonal hypergammaglobulinemia with a slight increase in immunoglobulin (Ig) G and IgA, and an increase in acute phase reactants (erythrocyte sedimentation rate [ESR] and C-reactive protein [CRP]). Autoimmunity markers were negative and no alterations in urine sediment were observed.

A punch biopsy of one of the chest lesions showed superficial and deep infiltrate with perivascular and periadnexal involvement (Fig. 2A), as well as perineural involvement (Fig. 2B). Observation at higher magnification revealed that the infiltrate consisted of plasma cells (Fig. 2C). Immunohistochemistry showed positive staining for κ and λ Ig light chains (Fig. 3), with no light chain restriction. Based on these observations, the differential diagnosis included other entities characterized by plasma-cell-rich infiltrate including infectious diseases (e.g. syphilis, leishmania), autoimmune diseases (e.g. lupus), and neoplastic diseases (e.g. plasmacytoma). Syphilis serology was negative. The hematology department performed peripheral blood tests, which showed no alterations in white blood cells or in the proteinogram. In the absence of any clinicopathologic correlation or signs of hematological disease, and given the negative syphilis serology and the presence of plasma-cell-rich infiltrate, a diagnosis of cutaneous plasmacytosis was established based on the pathological findings. In accordance with the recommendations of the hematology department, no extension study was carried out owing to the duration of the lesions and the absence of systemic signs, lymphadenopathy, organomegaly, or laboratory abnormalities.

Figure 2.

Pathology images. A, Panoramic image showing superficial and deep perivascular and periadnexal infiltrate (hematoxylin-eosin [HE], original magnification ×20). B, Higher magnification image showing perineural infiltrate (HE, original magnification ×40). C, Detail of the inflammatory infiltrate, which consists of plasma cells.

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Figure 3.

Immunohistochemistry images showing positive staining for κ (A) and λ (B) immunoglobulin light chains.

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