RESUMO
BACKGROUND: Erdheim Chester disease (ECD) is a rare form of non-Langerhans histiocytosis that still presents a diagnostic and clinical dilemma. CASE PRESENTATION: We present a rare case of ECD, young 31 male with atypical localisation and soft tissue presentation and no bone involvement. He started clinical investigations due to subcutaneous tumour mass in the lumbar spine that caused severe back pain. Skin biopsy revealed ECD with Immunohistochemistry CD68+, CD10+, CD11c+, vimentin+, S100A4+. Activating BRAFV600E mutation was positive from the tumour tissue. The patient was referred to the haematology department. PET CT was performed for initial disease staging. Treatment was started with corticosteroids (methylprednisolone 0.5 mg/kg per day), and after 7 days, a significant clinical improvement was noticed in terms of pain disappearance with no need for pain killers. After two weeks, treatment with interferon Alfa (IFN-α) was started in a dose of 3 million units 3 times per week. After 4 months of interim treatment PET, CT revealed a significant reduction of the tumour mass. Therapy with IFN-α was continued, and the patient is still clinically in good condition. CONCLUSION: It can be concluded that shortening the time of diagnosis of ECD is essential in treatment outcome of this disease. Still, large studies have to confirm the best treatment of this rare condition.