A patient with a papulo–nodular lesion on the shoulder

A man in his 40s presented with an asymptomatic erythematous, infiltrated plaque, topped by multiple papular and nodular lesions on the left shoulder that appeared 8 months prior (Figure 1). The patient reported no systemic symptoms, fever or weight loss. He had significant medical history, denied any recent travels complete clinical examination was otherwise normal, including lymph node areas. work-up blood test (blood cell count, C-reactive protein levels, hepatic, renal thyroid function, electrolytes, serum electrophoresis, infectious serologies for HIV, hepatitis B C syphilis), 18F-FDG PET/CT cranioencephalic magnetic resonance imaging (MRI) normal. punch biopsy performed 2a,b). Cutaneous Rosai–Dorfman disease (CRDD) (Sinus histiocytosis massive lymphadenopathy). Histological immunohistochemical (S-100 protein) analysis of skin specimen showed a characteristic feature emperipolesis 2a,b) strong staining histiocytes S-100 3) which confirmed diagnosis RDD. An increase IgG4-positive plasma cells also observed 4). Due to lack involvement, CRDD made. In this case, surgical resection performed. RDD, non–Langerhans histiocytosis, include painless noninflammatory cervical enlargement, fever, leukocytosis neutrophilia, elevated erythrocyte sedimentation rate, anaemia hypergammaglobulinemia.1 Extranodal involvement is 40% cases. rare benign form RDD characterized histiocytic proliferation exclusively located into skin.2, 3 We report observation CRDD, frequently misdiagnosed clinically. Patients have older mean age female predominance compared patients.2, 4 case herein concerned young (in 40s), has been rarely described. patients may usually yellow, reddish-brown violaceous papules, nodules plaques. Plaque nodule papules distinctive here. can be either single numerous, most common distribution these head upper part body. Diagnosis must supported biopsies histological immunochemistry analysis. representative histologic dense dermal infiltrate images (intact inflammatory histiocyte cytoplasm, lymphophagocytosis) mixed infiltrate. immunohistochemistry reveals expressing PS100, CD163 CD68, macrophagic markers, but not CD1a.2-4 numbers typical S100-positive histiocytes, importance as well quality quantity response variable.4 Although association between IgG4-related remains controversial, Histiocyte Society recommends evaluation all cases cells. cells, it our patient, should documented interpreted regarding clinical, serological radiological context.3 exact pathophysiology unknown, polyclonal cellular suggests reactive process rather than neoplastic one. link some infections suspected. Several are associated autoimmune diseases lymphomas.2 therefore indicated PET/CT, MRI tests. For localized disease, excision first choice. refractory cases, oral steroids, dapsone, thalidomide, methotrexate, retinoids, doxycycline imatinib proposed. prognosis good possibility spontaneous resolution.5, 6 Evolution seems extremely rare.4 Differential included primary cutaneous B-cell lymphoma (pCBCL), dermatofibrosarcoma protuberans infection due nontuberculosis mycobacterium. There three main subtypes pCBCL: marginal zone lymphoma, follicle centre diffuse large leg type. They manifest red-to-violaceous pink nodules, plaques tumours. based specific histologic, immunohistochemical, cytogenetic molecular features.7 Dermatofibrosarcoma low-grade slow-growing malignant sarcoma, presenting large, bumpy, multinodular tumour adherent surface without ulcerating it, infiltrating dermis hypodermis often beyond palpable limits. (monomorphous spindle storiform pattern) detection translocation t(17;22)(q22;q13), present 90% cases.8, 9 Clinical features mycobacterium polymorphic (nodules, plaques, abscesses, ulcers), multiple, one limb disseminated. considered presence uncharacterized eruption, especially immunocompromised patients. Histopathological findings nonspecific; tissue culture PCR assays necessary identify species.10 This illustrates appearance diagnostic challenge clinician. Fanny Ickx Axel De Greef literature search prepared manuscript. Diane Declaye Léo-Paul Secco were charge investigation process. Marie Baeck reviewed approved manuscript decided submit publication. authors conflict interest. given written informed consent use deidentified, anonymized, aggregated data details (including photograph) Data available request from authors.