A cytologic diagnosis of BRAF^V600E Erdheim-Chester disease on pericardial fluid

We report the case of a 74-year-old woman admitted to the emergency unit for resting dyspnea. Clinical presentation, cardiac MRI and echocardiography were consistent with cardiac tamponade requiring emergency pericardiocentesis. Cytologic examination of the pericardial fluid revealed the presence of CD68^pos CD1a^neg S100^neg foamy histiocytes (Fig. 1). Additional investigations complied with the diagnosis of Erdheim-Chester histiocytosis. Treatment with αIFN was initiated but the patient developed severe neutropenia that contraindicated further administration. The detection of BRAF^V600E mutation on histiocytes isolated from the pericardial liquid and CNS involvement (cerebral masses) prompted the administration of vemurafenib, a selective BRAF^V600E kinase inhibitor. Four months after the initiation of low-dose vemurafenib, pericarditis almost resolved and cerebral masses decreased by 50% (Fig. 2). To our knowledge, analysis of pericardial fluid allowing the diagnosis of Erdheim-Chester disease and the detection of the BRAF^V600E mutation has in fact been rarely described in the literature. This case report and the successful evolution under vemurafenib also support the use of BRAF^V600E inhibitors in αIFN-intolerant patients with BRAF^V600E mutation, particularly in case of heart and central nervous system involvement.