[Mosquito bite allergies terminating as hemophagocytic histiocytosis: report of a case].

A 21-year-old woman had suffered from repeated vasculitis and panniculitis with fever and chills after following mosquito bites since age 7. These manifestations were confirmed with a direct mosquito bite test during her admission to another hospital at age 17. The patient presented to our hospital with progressive dyspnea, productive cough and intermittent fever for one week. In addition to the bilateral infiltrative lesions on chest roentgenography, hepatosplenomegaly with an abnormal liver function test, pancytopenia, and elevated IgE were also detected. Blood and sputum cultures grew no microorganisms. Epstein-Barr virus-IgM, Cytomegalovirus-IgM and Mycoplasma pneumonia antibodies were all negative. Bone marrow aspiration and biopsy revealed histiocytosis with hemophagocytosis. No atypical histiocyte was found. The patient was put on dexamethasone treatment with improvement. Unfortunately, symptoms relapsed two weeks later. A repeated bone marrow aspiration and biopsy revealed a picture similar to the previous one. Despite antibiotic administration and ventilator support, a rapidly deteriorated course terminated in the patient's death by respiratory failure. Mosquito bite allergies were reported to be associated with malignant histiocytosis in Japan. However, atypical histiocytes were not found in our case upon repeated bone marrow aspirations, biopsies and skin biopsies. Mature histiocytes with hemophagocytosis were prominent instead. Reactive histiocytosis was thus favored rather than malignant histiocytosis. Although opportunistic infection cannot be excluded, we propose that a mosquito bite allergy with consequent histiocytic activation by antigen, immune complex or IgE is the possible pathogenetic mechanism for hemophagocytic histiocytosis in this patient.