[A rare cause of loss of consciousness: mastocytosis. Apropos of 3 cases].

The authors report three cases of syncope due to systemic mastocytosis. This is a rare cause of syncope but should be recalled in certain circumstances. In the light of these cases, the authors review the literature with respect to this unusual presentation. Syncope may occur at any age. Loss of consciousness may be more or less complete, brief or prolonged, isolated or recurrent and usually accompanied by prodromal symptoms. The least controversial physiopathogenic mechanism of these syncopes is intense vasoplegia induced by the release of vasoactive mediators, especially histamine. When there is a clinical suspicion of mastocytosis, even in the absence of skin changes, the diagnosis is confirmed by biopsy which shows abnormally high numbers of mastocytes irrespective of the organ biopsied. The treatment of acute forms with collapse is based on intravenous infusion of macromolecular fluids and injections of epinephrine. Prevention is by drugs which inhibit the synthesis of histamine, the degranulation of mastocytes and the production of prostaglandin D2.