RESUMO
BACKGROUND: Langerhans cell histiocytosis previously known as histiocytosis X is a rare disease of children and young adults with a very broad clinical spectrum. In children, its annual incidence is estimated between 0.2-0.5 per 100,000. CASE REPRESENTATION: An 8-year-old Moroccan girl with no known personal or family history presented to our institution with painful swelling of both forearms. An X-ray and magnetic resonance imaging were inconclusive. We then performed a biopsy curettage (of her left forearm). Microscopic analysis followed by immunohistochemical analysis disclosed a diagnosis of Langerhans cell histiocytosis. No chemotherapy was necessary. Clinical and radiological improvement was achieved after 6 months. CONCLUSION: The particularity of this observation is the bilaterality of the lesion on both forearms and it has not previously been reported. Langerhans cell histiocytosis should be included in the differential diagnosis of osteomyelitis and Ewing's sarcoma.