S-100-negative indeterminate cell histiocytosis: A case report of an 8-month-old boy

Abstract

Introduction: Indeterminate cell histiocytosis (ICH) is a rare cutaneous neoplastic disorder, characterised typically by the presence of dendritic cells with CD1a, S-100 and CD68 positivity. The absence of Birbeck's granules differentiates it from Langerhans cell histiocytosis (LCH). We present a case of ICH with an atypical immunohistochemical profile (CD1a positive with S-100 negative) in an infant boy. Case presentation: An 8-month-old Caucasian boy presented with four-month history of multiple (20-30) erythematous papules over his forearms, thighs, trunk and scalp, with sparing of the mucosa. The lesions appeared asymptomatic and he was otherwise healthy, with constipation as his only medical condition. On examination, he had no obvious congenital abnormalities, neurologic deficits or organomegaly. His bloods tests, chest X-ray, and abdominal ultrasound were unremarkable. Two punch biopsies showed an infiltrate of histiocytoid cells throughout dermis with intervening zones of necrosis. Immunophenotype was positive for CD1a and CD43, patch weak CD68 and negative for Langerin, CD45 and s100, favouring a diagnosis of ICH over LCH. The cutaneous lesions were treated with topical corticosteroids with good effect to date, and the patient will have follow-up with the dermatology and medical oncology teams for ongoing screening for associated malignancies. Discussion: To date, there have been less than 100 cases of ICH, with even rarer reports of ICH with S-100 negativity. This case is significant as our patient is the youngest documented case of ICH in the medical literature and contributes towards enabling a greater understanding of the pathogenesis and management of this variant.L6347383472021-04-15 <br />