Megadose methylprednisolone for Kasabach-Merritt syndrome.
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We report a 7-year-old girl with hemophagocytic lymphohistiocytosis and an uncommon complication of vascular retinopathy and visual sequelae. She was also verified to be complicated with dysfibrinogenemia. The patient was treated with etoposide, dexamethasone, and cyclosporin A. During the fifth hospital week, a generalized tonic-clonic convulsion developed followed by deep coma. When she regained full consciousness, she complained of a visual disturbance. The ophthalmologic examination showed bilateral extensive retinal edema with numerous cotton-wool spots, indicative of vaso-occlusive retinopathy. This is inconsistent with the main finding of previous cases with ocular involvement, namely papilledema. Severely reduced visual acuity and visual field defects remained in both eyes even after systemic therapy. An awareness of this rare but serious complication is important because it may be preventable by early institution of chemotherapy. The pathogenesis of the retinopathy is also discussed.
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In order to investigate the cause of hypofibrinogenemia in familial hemophagocytic lymphohistiocytosis (FHL), formalin-fixed and paraffin-embedded tissue sections of the spleen obtained at autopsy were examined by using immunohistochemical methods for the presence of fibrinogen antigens, and such antigens were detected in approximately 10% of the histiocytes in a diffuse staining pattern. This finding indicates uptake of fibrin and/or fibrinogen molecules by activated histiocytes and suggests that hypofibrinogenemia of FHL is caused by the direct action of activated histiocytes on factor X through Mac-1 receptors, subsequent activation of the common pathway of the coagulation protease cascade, and uptake of fibrin and/or fibrinogen molecules by such cells.
The authors describe the total excision of a huge occipital hemangioendothelioma in an infant with thrombocytopenia, hypofibrinogenemia, and anemia; treatment was followed by normalization of platelet count, blood cell count, and level of fibrinogen. Histological and clincial studies support the concept the disseminated intravascular coagulation was related to the thrombocytopenia and coagulation deficits found in this case.
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Staphylococcus aureus undergoes a density-dependent conversion in phenotype from tissue-adhering to tissue-damaging and phagocyte-evading that is mediated in part by the quorum-sensing operon, agr, and its effector, RNAIII. Contributions of host factors to this mechanism for regulating virulence have not been studied. We hypothesized that fibrinogen, as a component of the inflammatory response, could create spatially constrained microenvironments around bacteria that increase density independently of bacterial numbers and thus potentiate quorum-sensing-dependent virulence gene expression. Here we show that transient fibrinogen depletion significantly reduces the bacterial burden and the consequential morbidity and mortality during experimental infection with wild-type S. aureus, but not with bacteria that lack expression of the quorum-sensing operon, agr. In addition, it inhibits in vivo activation of the promoter for the agr effector, RNAIII, and downstream targets of RNAIII, including alpha hemolysin and capsule production. Moreover, both in vitro and in vivo, the mechanism for promoting this phenotypic switch in virulence involves clumping of the bacteria, demonstrating that S. aureus responds to fibrinogen-mediated bacterial clumping by enhancing density-dependent virulence gene expression. These data demonstrate that down-modulation of specific inflammatory components of the host that augment bacterial quorum sensing can be a strategy for enhancing host defense against infection.
Following envenomization by Echis carinatus sochureki, a professional snake handler developed a profound coagulopathy manifested by hemorrhage from the bite site, venipuncture sites and gums; coagulation testing revealed prothrombin and partial thromboplastin times greater than 150 seconds, a fibrinogen of 0 mg%, and marked elevation of fibrin degradation products. In addition, protein C antigen levels were undetectable. The coagulopathy was treated with cryoprecipitate; two different antivenoms were also administered with uncertain benefit. Subsequently, the properties of the venom and antivenoms were studied. Venom did not directly clot fibrinogen; however, venom concentrations as low as 0.2 micrograms/ml caused significant prothrombin activation. In addition, venom activated protein C in the absence of thrombomodulin, and this activity was inhibited by hirudin. The ability of four commercial antivenoms to neutralize the venom prothrombinase and hemorrhagic activity was measured. Three of the four antivenoms partially neutralized venom-induced prothrombin activation. Extreme differences in efficacy were found among the four antivenoms in neutralizing venom hemorrhagic activity in mice. This case illustrates the difficulty in managing the complex coagulopathy that can result from exotic snake envenomization, and identifies a new coagulant property of Echis carinatus venom (protein C activation).
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OBJECTIVES: To review the state of the art relating to congenital dysfibrinogenemia as a potential risk factor for thrombosis, as reflected by the medical literature and the consensus opinion of recognized experts in the field, and to make recommendations for the use of laboratory assays for assessing this thrombotic risk in individual patients. DATA SOURCES: Review of the medical literature, primarily from the last 10 years. DATA EXTRACTION AND SYNTHESIS: After an initial assessment of the literature, key points were identified. Experts were assigned to do an in-depth review of the literature and to prepare a summary of their findings and recommendations. A draft manuscript was prepared and circulated to every participant in the College of American Pathologists Conference on Diagnostic Issues in Thrombophilia. Each of the key points and associated recommendations were then presented for discussion at the conference. Recommendations were accepted if a consensus of experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form. CONCLUSIONS: Consensus was reached on 5 conclusions and 2 recommendations concerning the use of testing for dysfibrinogens in the assessment of thrombotic risk in individual patients. Detailed discussion of the rationale for each of these recommendations is found in the text of this article. Compared with the other, more common hereditary thrombophilias, dysfibrinogenemia encompasses a diverse group of defects with varied clinical expressions. Congenital dysfibrinogenemia is a relatively rare cause of thrombophilia. Therefore, routine testing for this disorder is not recommended as part of the laboratory evaluation of a thrombophilic patient. This is an evolving area of research, and further clinical studies may change these recommendations in the future.