A 72-year-old woman was referred to our clinic for evaluation of asymptomatic, erythematous papules and nodules on her trunk, which had been present for 3 months. The patient's medical history revealed that 2 years earlier she was diagnosed with right breast adenocarcinoma (T2 N1 M0, stage IIB, infiltrating ductal type). She underwent mastectomy and axillary lymphadenectomy, followed by systemic chemotherapy and local radiation therapy. The patient reported that several months prior to this presentation she had been diagnosed with scabies and had been treated with benzyl benzoate 10% cream. Physical examination showed the presence of multiple papular and nodular lesions, varying from 0.5 to 1.5 cm. The lesions were located at the site of the mastectomy scar, on the right axilla (Figure 1), and on the abdomen. She was otherwise healthy and no lymphadenopathy was detected.
On the basis of a clinical impression of cutaneous metastases from breast carcinoma, an excisional biopsy of a papular lesion from the right axilla was performed for histopathologic examination. Hematoxylin-eosin–stained tissue sections showed the presence of a top-heavy, dense, perivascular, and interstitial polymorphous infiltrate, located in the superficial and deep dermis (Figure 2). The infiltrate was composed of small lymphocytes, histiocytes, plasma cells, and numerous eosinophils (Figure 3). No pleomorphic cells, mitoses, or areas of necrosis were seen. The epidermis was slightly hyperplastic. Immunohistochemical analysis revealed a mixed infiltrate with a predominance of CD3- and CD4-positive T lymphocytes, clusters of CD20-positive B lymphocytes with germinal centers (Figure 4), and CD68-positive histiocytes. B lymphocytes exhibited a polytypic expression of κ and λ light chains. Molecular analysis of immunoglobulin (Ig) H and T-cell receptor genes showed a germline polyclonal configuration.
What is your diagnosis?
Pathologic Diagnosis: B-Cell Pseudolymphoma
Cutaneous pseudolymphomas encompass a heterogeneous group of T-cell and B-cell benign reactive lymphoproliferative diseases resembling malignant lymphomas clinically and, above all, histopathologically. T-cell pseudolymphomas are histopathologically characterized by a superficial bandlike infiltrate located in the upper dermis or, rarely, by a nodular pattern.1
B-cell pseudolymphomas commonly show a nodular or diffuse polymorphous infiltrate throughout the dermis. The infiltrate consists of lymphocytes admixed with histiocytes, eosinophils, and plasma cells. In some cases, a small number of large lymphocytes with atypical nuclei and prominent nucleoli may be observed. Germinal centers are usually present and can be divided into 2 types: (1) the small-cell nodular form, which shows typical center formation and lacks cellular pleomorphism; and (2) the large-cell nodular form, which is characterized by large pleomorphic lymphocytes and many mitotic figures, and which can be difficult to distinguish from lymphoma. Other cell types that may be found in germinal centers are T-helper cells, macrophages with tingible bodies, and dendritic cells. In rare instances, plasma cells may be the predominant cells.1–3 Establishing a histopathologic differential diagnosis between cutaneous B-cell pseudolymphoma and B-cell lymphoma may be very difficult. An immunohistochemical finding of monotypic light chain expression or lack of detectable immunoglobulin in cutaneous B-cell lymphoma is the most important criterion in the differential diagnosis.1,4
The diagnosis should always be based on the combination of clinical, histopathologic, immunohistochemical, and gene rearrangement findings.5,6 In our patient, the medical history, the presence of a mixed cellular infiltrate, the polyclonal expression of κ and λ light chains, and the germline configuration of IgH and T-cell receptor genes gave support to the diagnosis of scabies-induced B-cell pseudolymphoma.
Nodular scabies appears with erythematous brownish papules and/or nodules and is most frequently located on the elbows, genitalia, and axillae. Lesions are often extremely pruritic and may persist for several months after treatment.7 Nodular scabies is the most common example of persistent mixed lymphomatoid reaction to arthropod bites, likely representing an hypersensitivity reaction to retained mite parts or persisting antigens, although mites are only seldom identified in long-standing lesions.8,9 When the causative agent of pseudolymphoma is known, its removal results in clinical remission of cutaneous lesions. In idiopathic cases, treatment is not mandatory; lesions tend to be chronic and indolent, and spontaneous regression may occur over months or a few years, even if recurrence has been reported.7 In selected patients, treatment may include surgical excision, cryosurgery, local radiation therapy, and topical or intralesional corticosteroids.7,10 Our patient refused any therapy, and 3 months after initial observation the clinical features were unchanged.
References
The authors have no relevant financial interest in the products or companies described in this article.