DP24 Asymptomatic unilateral and linear papules and plaques in a female child

Abstract

Cutaneous reticulohistiocytosis is a rare subtype of non-Langerhans cell histiocytosis. It includes three different entities, namely ‘reticulohistiocytoma (RH),’ ‘diffuse cutaneous reticulohistiocytosis’ and ‘multicentric reticulohistiocytosis’ (MR). Solitary RH is the most commonly encountered form, while diffuse cutaneous RH (also known as single-system multifocal reticulohistiocytosis or SSmf RH according to latest classification) is a rare entity with around 30 reports in literature. A 7-year-old girl presented with asymptomatic skin-coloured-to-erythematous papules and nodules involving the right upper limb and back for 6 months duration. The lesions started over the dorsum of the right hand and gradually progressed in size and number to involve the forearm, arm and ipsilateral half of the back. There were no systemic symptoms. Two differential diagnoses of sarcoidosis and zosteriform cutaneous metastasis were considered. A punch biopsy for histopathology from the papule over the mid-forearm showed an atrophic epidermis and grenz zone and a dense diffuse dermal infiltrate. The infiltrate was composed of plump histiocytes, giant cells (oncocytic type), foamy histiocytes and lymphocytes. Immunohistochemistry (IHC) was positive for CD68 and negative for S100 and CD207. After the histopathology and IHC results were available, a diagnosis of multiple reticulohistiocytomas in a unilateral distribution was considered. Screening for systemic disease with chest X-ray and electrocardiography was negative. The child was managed conservatively and the parents counselled regarding prognosis and follow-up. SSmf RH is characterized by multiple lesions involving the trunk and/or extremities, with sparing of the fingers and juxta-articular and paronychial regions (unlike MR) and supportive IHC findings. The diagnosis is important as screening for systemic involvement is necessary to rule out MR, which has major prognostic importance. Once systemic involvement is excluded, it has a good prognosis, with no cases progressing to systemic involvement (longest follow-up of 5 years). The rarity of this case and importance of diagnosis make it significant.