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Langerhans cell histiocytosis (LCH) is a rare disease affecting both genders and can occur at any age. It often evolves through successive flares, and its severity varies from benign forms that don't require treatment to life threatening disease. Some patients have important functional impairment with psychological and social consequences and prolonged disability. LCH may affect only one organ, with uni- or multifocal involvement or be multisystem disease involving multiple organs. The organs most frequently involved are bones, lung, skin and the endocrinal system. Pulmonary LCH is strongly related to smoking. Some patients have mixed histocytosis combining LCH and other histiocytic disorders. The diagnosis relies on the histological study of tissues samples, and shows tissue infiltration with large cell with pale cytoplasm and reniform nucleus, staining for CD1a and Langerin (CD207) on immunohistochemistry. The BRAF V600E mutation is observed in tissue samples in approximately half of patients and the activation of the RAS-RAF-MEK-ERK pathway has been shown to be constantly activated in LCH lesions, regardless the BRAF status. These findings represent an important forward step in the understanding of the physiopathology of the disease. Treatment must be adapted to the severity of the disease and goes from conservative observation to systemic chemotherapy. Therapies targeting the RAS-RAF-MEK-ERK pathway are promising treatments for progressive disease., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

Giant-cell arteritis (GCA) and Takayasu arteritis (TAK) are primary systemic granulomatous large-vessel vasculitides. Whether both entities represent distinct phenotypic expressions of a shared etiopathogenic process remains hypothetical. GCA more commonly affects subjects of northern European background while the clinical observation that TAK might be more common in populations of Asian or African ancestry needs to be confirmed by epidemiological studies. Distinct human leukocyte antigen class II associations were identified as genetic risk factors of GCA and TAK. The increasing incidence of GCA also suggests an environmental cause. Temporal artery biopsy is the main diagnostic test for GCA, although MRI and Doppler ultrasonography of the temporal or occipital arteries may also reveal vessel wall inflammation. MRI, CT and positron emission tomography with 18F fluodeoxyglucose have progressively replaced conventional invasive imaging modalities for study of large-vessel disease. The diagnostic accuracy of these 3 imaging modalities seems equivalent, but their value in the follow-up of GCA and TAK is less clear. According to studies based on modern imaging techniques, 70-80% of patients with newly diagnosed GCA show an involvement of the aorta and/or the major branches of the aorta. Glucocorticoids are the reference therapy for GCA. Adjunctive therapy, notably with methotrexate, appears to enhance disease control and reduce glucocorticoid exposure. IL-6 blockade has hope as a new treatment option for GCA. Principles of therapy for TAK are similar to those of GCA, except that TNFα blockers, particularly infliximab, seem to show good results in TAK and revascularization procedures are an important part of the TAK therapy., (Copyright © 2012. Published by Elsevier Masson SAS.)