[Pelvic mass in 70 years old patient: Difficult diagnosis of Erdheim-Chester disease]. / Masse pelvienne chez un patient de 70 ans : diagnostic difficile de maladie d'Erdheim-Chester.

Erdheim-Chester disease (EC) is a rare disease that is included in Group L in the 2016 revised classification of Langheransian histiocytoses. This disease may be clinically asymptomatic or manifest as a multi-systemic and life-threatening condition. All organs can be affected but typically there is bone involvement, retroperitoneal fibrosis, pituitary involvement, involvement of large vessels, lung, pleura or central nervous system. We are reporting a 70-year-old patient who, as of 2014, had a pelvic mass with retroperitoneal fibrosis and large vessel vasculitis without a definite diagnosis. Histological and molecular examination of the surgical specimen of the pelvic mass with the discovery of the BRAF V600E mutation provided new elements for the definitive diagnosis of Erdheim-Chester disease. We will describe the clinical, histological and molecular features to be known in EC disease.

BRAF-mutated histiocytosis of the skull lacking the expression of Langerhans cell markers.

Langerhans cell histiocytosis (LCH) is a rare condition affecting children more frequently than adults. LCH can involve any organ in the body and has a wide spectrum of clinical presentation from a single self-healing bone lesion to a multisystemic life-threatening disease. The diagnosis of LCH requires histology with compatible clinical and radiological findings. Positive immunochemistry for both CD1a and CD207 is required for a definitive diagnosis of LCH. The majority of LCH shares oncogenic BRAFV600E mutation. We report the case of a 55-year-old adult who presented with a single lytic self-healing lesion of the skull, invading adjacent soft tissues. The histology and cytology were also typical of LCH, and tumor cells contained the BRAFV600E mutation. However, histiocytes were negative for CD1a and CD207. We suggest that this case might be considered as LCH, despite its abnormal phenotype.
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