Purpose or Case Report: Langerhans cell histiocytosis (LCH) is a rare neoplastic disorder of abnormal proliferation of Langerhans cells affecting predominantly pediatric populations; sites of involvement include cutaneous, osseous, hematopoietic, and multisystem disease (1). Cutaneous involvement is common in children, though thymic involvement is rarely described (2). We report a case of an 8-month-old female infant with a dyad of cutaneous and thymic LCH. The purpose of this paper is to highlight a potentially underdiagnosed manifestation of infantile LCH and consider thymic sonography in infant LCH staging evaluation.

A one-month old female presented with skin lesions and pruritus suspicious for atopic dermatitis failing to respond to therapy. Punch biopsy demonstrated cutaneous LCH. Staging non-contrast chest computed tomography (CT) showed multiple very faint calcifications in the thymus (figure 1) which could have been obscured by intravenous contrast administration. Ultrasound demonstrated multiple echogenic foci in the thymus (figure 2). Pathology confirmed thymic LCH. Throughout her presentation, the patient’s clinical symptoms of LCH were limited to diffuse pruritic cutaneous lesions. Thymic involvement changed patient management to chemotherapy infusion. At the time of this report she has shown no signs of disease progression and she remains clinically stable.
Methods & Materials: Case Report
Results: Cutaneous involvement is common in children and may spontaneously regress, respond to treatment, or progress to multisystem disease (2). Isolated thymic involvement is rare and is described only by a handful of isolated case reports, and cutaneous and thymic involvement have been rarely published (3-5). Thymic LCH affects only an estimated 2.6% based on 50 case reports in 50 years presented as a series (6). Prognosis of LCH is influenced by the specific organs involved and extent of involvement, however the prognostic significance of thymic involvement is unknown.
The dyad of cutaneous and thymic LCH is rare, though potentially underestimated as CT findings may be subtle or masked by contrast. Ultrasound findings in this case and prior case reports were clear. Ultrasonography is not standard in staging evaluation of LCH; we suspect that thymic LCH is underdiagnosed.
Conclusions: This report highlights a rare dyad of cutaneous and thymic LCH in an infant. We propose thymic ultrasound during staging evaluation of LCH, especially in infant populations.