Unilesional, single‐system cutaneous Langerhans cell histiocytosis in an 11‐month‐old infant

An 11-month-old male infant was referred to our department with a six-month history of a progressive, red-brown nodule with central erosion, measuring 1.5 cm in diameter and firm to palpation, on the dorsum of his right foot (Figure 1a). Dermatoscopy revealed a symmetrical bizonal architecture with a reddish outer rim made up of punctate vessels and an inner erosive area with white scales and brown globules (Figure 1b). The remaining integument, the mucosa, and subcutaneous lymph nodes were unremarkable. The lesion was completely excised to rule out melanoma and other differential diagnoses including juvenile xanthogranuloma, atypical Spitz tumor, or solitary mastocytoma. Histopathology showed hyperparakeratosis and a dense dermal infiltrate of large epithelioid cells with pale cytoplasm and indented reniform nuclei (Figure 2a), with focal epidermotropism and multiple foci of intraepidermal cell accumulations. The infiltrate was accompanied by scattered lymphocytes, eosinophils, and extravasated erythrocytes. Large epithelioid cells stained positive for CD1a, CD207, and S-100 (Figure 2b), thus confirming Langerhans cell histiocytosis (LCH). Further pediatric workup as well as a complete blood count, liver and kidney function tests, serum electrophoresis, ultrasound of the abdomen and lymph nodes, and a skeletal survey were unremarkable, leading to the diagnosis of unilesional, single-system, cutaneous LCH. No new lesions have occurred in the four months since the initial diagnosis. Langerhans cell histiocytosis represents a clonal proliferation of abnormal myeloid dendritic cells with subsequent accumulation in different organs [1]. Most commonly affecting infants and children [2], the clinical spectrum of LCH ranges from single-system disease (e. g. skin or bone) to multisystem disease (e. g. skin, liver, spleen, and bone marrow) with potentially fatal outcome [2]. Skin lesions of LCH frequently resemble seborrheic dermatitis or eczema and are predominantly found on the scalp or face [3]. Skin involvement may be observed in spontaneously resolving skin-limited disease as well as in potentially life-threatening multisystem disease [2, 4]. Single-system, cutaneous disease – as diagnosed here – is rare and accounts for only 2 % of LCH cases [5]. LCH confined to the oral mucosa is equally rare [6]. Hashimoto and Pritzker first described self-limited cutaneous LCH (SLCLCH) in 1973 [7]. More recently, Wheller et al. reported a rare series of 35 SLCLCH cases [8]. In our case, the solitary lesion was completely excised; future spontaneous regression may therefore only be assumed based on available data. Skin lesions in SLCLCH are congenital or appear shortly after birth. The clinical presentation typically consists of red-brown or purple, firm papules preferentially located on the head, trunk, extremities, or at acral sites [8]. The trunk is the most commonly reported location (37 %) and men are predominantly affected (63 % of reported cases) [8]. About 30 % of SLCLCH cases show solitary lesions, whereas the majority of patients have multiple lesions [9]. The differentiation between self-limited LCH and LCH forms with progressive systemic involvement is crucial, given that extracutaneous involvement is associated with a worse prognosis and may require systemic treatment (e. g. chemotherapy) [8]. As clinical aspects and histopathology alone are insufficient with respect to differentiating the two forms, detailed workup and close follow-up examinations are required. Zunino-Gouturbe et al. have suggested regular physical exams at least every two years [9]. There are as yet no reports on systemic involvement in self-limited LCH with solitary lesions [8]. By contrast, several authors have reported multilesional self-limited LCH