Haemolytic-uraemic syndrome and thrombotic thrombocytopenic purpura--new insights into underlying biochemical mechanisms

Platelet and HIV Interactions and Their Contribution to Non-AIDS Comorbidities

Platelets are anucleate cytoplasmic cell fragments that circulate in the blood, where they are involved in regulating hemostasis. Beyond their normal physiologic role, platelets have emerged as versatile effectors of immune response. During an infection, cell surface receptors enable platelets to recognize viruses, resulting in their activation. Activated platelets release biologically active molecules that further trigger host immune responses to protect the body against infection. Their impact on the immune response is also associated with the recruitment of circulating leukocytes to the site of infection. They can also aggregate with leukocytes, including lymphocytes, monocytes, and neutrophils, to immobilize pathogens and prevent viral dissemination. Despite their host protective role, platelets have also been shown to be associated with various pathophysiological processes. In this review, we will summarize platelet and HIV interactions during infection. We will also highlight and discuss platelet and platelet-derived mediators, how they interact with immune cells, and the multifaceted responsibilities of platelets in HIV infection. Furthermore, we will give an overview of non-AIDS comorbidities linked to platelet dysfunction and the impact of antiretroviral therapy on platelet function.

Traumatic injury results in prolonged circulation of ultralarge von Willebrand factor and a reduction in ADAMTS13 activity

BACKGROUND

Increases in plasma von Willebrand Factor (VWF) levels, accompanied by decreases in the metalloprotease ADAMTS13, have been demonstrated soon after traumatic injury while downstream effects remain unclear.

STUDY DESIGN AND METHODS

A cohort of 37 injured trauma patients from a randomized control trial investigating the use of prehospital plasma transfusion were analyzed for activity and antigen levels of ADAMTS13 and VWF at 0 and 24 hours after admission. Relevant clinical data were abstracted from the medical records. Trauma patient plasma was analyzed via agarose gel electrophoresis to evaluate the effects of injury on VWF multimer composition compared to healthy controls.

RESULTS

von Willebrand factor levels were elevated at presentation (189% [110%-263%] vs. 95% [74%-120%]), persisting through 24 hours (213% [146%-257%] vs. 132% [57%-160%]), compared to healthy controls. Ultralarge VWF (UL-VWF) forms were elevated in trauma patients at both 0 and 24 hours, when compared to pooled normal plasma (10.0% [8.9%-14.3%] and 11.3% [9.1%-21.2%], respectively, vs. 0.6%). Circulating plasma ADAMTS13 activity was decreased at 0 hours (66% [47%-86%] vs. 100% [98%-100%]) and at 24 hours (72.5% [56%-87.3%] vs. 103% [103%-103%]) in trauma patients. ADAMTS13 activity independently predicted the development of coagulopathy and correlated with international normalized ratio, thromboelastography values, injury severity, and blood product transfusion.

CONCLUSION

Traumatic injury is associated with acute coagulopathy that is characterized by increased UL-VWF multimers and reduction in ADAMTS13, which correlates with blood loss, transfusion requirement, and injury severity. These findings suggest the potential for future trials targeting ADAMTS13 repletion to enhance clearance of VWF multimers.

ADAMTS13: origins, applications, and prospects

ADAMTS13 is an enzyme that acts by cleaving prothrombotic von Willebrand factor (VWF) multimers from the vasculature in a highly regulated manner. In pathologic states such as thrombotic thrombocytopenic purpura (TTP) and other thrombotic microangiopathies (TMAs), VWF can bind to the endothelium and form large multimers. As the anchored VWF chains grow, they provide a greater surface area to bind circulating platelets (PLTs), generating unique thrombi that characterize TTP. This results in microvasculature thrombosis, obstruction of blood flow, and ultimately end-organ damage. Initial presentations of TTP usually occur in an acute manner, typically developing due to an autoimmune response toward, or less commonly a congenital deficiency of, ADAMTS13. Triggers for TMAs that can be associated with ADAMTS13 deficiency, including TTP, have been linked to events that place a burden on hemostatic regulation, such as major trauma and pregnancy. The treatment plan for cases of suspected TTP consists of emergent therapeutic plasma exchange that is continued on a daily basis until normalization of PLT counts. However, a subset of these patients does not respond favorably to standard therapies. These patients necessitate a better understanding of their diseases for the advancement of future therapeutic options. Given ADAMTS13's key role in the cleavage of VWF and the prevention of PLT-rich thrombi within the microvasculature, future treatments may include anti-VWF therapeutics, recombinant ADAMTS13 infusions, and ADAMTS13 expression via gene therapy.

Gastroenteritis in an adult female revealing hemolytic uremic syndrome: Case report

Nowadays acute gastroenteritis infection caused by Escherichia coli (E. coli) O157:H7 is frequently associated with hemolytic uremic syndrome (HUS), which usually developed after prodromal diarrhea that is often bloody. The abdominal pain accompanied by failure kidney is a suspicious symptom to develop this disorder. Their pathological characteristic is vascular damage which manifested as arteriolar and capillary thrombosis with abnormalities in the endothelium and vessel walls. The major etiological agent of HUS is enterohemorragic (E coli) strain belonging to serotype O157:H7. The lack of papers about HUS associated to gastroenteritis lead us to report this case for explain the symptoms that are uncommon. Furthermore, this report provides some strategies to suspect and make an early diagnosis, besides treatment approach to improving outcomes and prognosis for patients with this disorder.

Exchange transfusion for neonate with haemolytic uremic syndrome

Introduction

Haemolytic uremic syndrome (HUS) is one of the most common causes of acute renal failure in children but it is uncommon in newborns. To our knowledge only five cases have been reported so far (probably underreported). The known modalities of treatment include transfusion of plasma and plasmapheresis. We report a case of neonatal HUS for whom we performed an exchange transfusion to good effect.

Case description

A term vaginally born baby, meconium stained and floppy at birth presented with severe anaemia in the first few hours of life. The baby later on developed renal failure and blood picture was suggestive of severe thrombocytopenia and microangiopathic haemolytic anaemia. No extra renal manifestations of birth asphyxia were noted. A double volume exchange transfusion was performed relatively early and subsequently platelet and haemoglobin stabilised and renal failure improved.

Discussion and evaluation

The clinical impression in this case was convincing of neonatal HUS, likely attributable to birth asphyxia but needs to be differentiated from disseminated intravascular coagulation (DIC) and thrombotic thrombocytopenic purpura (TTP). The coagulation profile is usually normal in HUS but it is abnormal in DIC, whereas in TTP one would find hyperbilirubinemia, increased creatinine, haemolysis etc. TTP is rare but not very uncommon in infancy. Congenital TTP is attributed to an inherent deficiency of ADAMTS-13, which is a vWF-cleaving metalloprotease. Irrespective of the etiology of HUS in our case, a dramatic response was observed with exchange transfusion. Transfusion of fresh frozen plasma (FFP) and plasmapheresis are known treatment modalities. FFP replaces the missing or altered complement factors and plasmapheresis removes antibodies, immune complexes and toxins. An exchange transfusion combines both these functions.

Conclusions

In the absence of facilities for plasmapheresis, exchange transfusion is a good alternative.

Update on von Willebrand factor multimers: focus on high-molecular-weight multimers and their role in hemostasis

Normal hemostasis requires von Willebrand factor (VWF) to support platelet adhesion and aggregation at sites of vascular injury. VWF is a multimeric glycoprotein built from identical subunits that contain binding sites for both platelet glycoprotein receptors and collagen. The adhesive activity of VWF depends on the size of its multimers, which range from 500 to over 10 000 kDa. There is good evidence that the high-molecular-weight multimers (HMWM), which are 5000-10 000 kDa, are the most effective in supporting interaction with collagen and platelet receptors and in facilitating wound healing under conditions of shear stress. Thus, these HMWM of VWF are of particular clinical interest. The unusually large multimers of VWF are, under normal conditions, cleaved by the plasma metalloproteinase ADAMTS13 to smaller, less adhesive multimers. A reduction or lack of HMWM, owing to a multimerization defect of VWF or to an increased susceptibility of VWF for ADAMTS13, leads to a functionally impaired VWF and the particular type 2A of von Willebrand disease. This review considers the biology and function of VWF multimers with a particular focus on the characterization of HMWM - their production, storage, release, degradation, and role in normal physiology. Evidence from basic research and the study of clinical diseases and their management highlight a pivotal role for the HMWM of VWF in hemostasis.

Complement factor H gene (CFH) polymorphisms C-257T, G257A and haplotypes are associated with protection against severe dengue phenotype, possible related with high CFH expression

Four genetic polymorphisms located at the promoter (C-257T) and coding regions of CFH gene (exon 2 G257A, exon 14 A2089G and exon 19 G2881T) were investigated in 121 dengue patients (DENV-3) in order to assess the relationship between allele/haplotypes variants and clinical outcomes. A statistical value was found between the CFH-257T allele (TT/TC genotypes) and reduced susceptibility to severe dengue (SD). Statistical associations indicate that individuals bearing a T allele presented significantly higher protein levels in plasma. The -257T variant is located within a NF-κB binding site, suggesting that this variant might have effect on the ability of the CFH gene to respond to signals via the NF-κB pathway. The G257A allelic variant showed significant protection against severe dengue. When CFH haplotypes effect was considered, the ancestral CG/CG promoter-exon 2 SNP genotype showed significant risk to SD either in a general comparison (ancestral × all variant genotypes), as well as in individual genotypes comparison (ancestral × each variant genotype), where the most prevalent effect was observed in the CG/CG × CA/TG comparison. These findings support the involvement of -257T, 257A allele variants and haplotypes on severe dengue phenotype protection, related with high basal CFH expression.

Thrombotic microangiopathy after living-donor liver transplantation

Thrombotic microangiopathy (TMA) is an infrequent but severe life-threatening disorder in solid organ transplant recipients. Few studies of TMA in living donor liver transplant (LDLT) recipients, however, have been reported. We investigated the clinical characteristics and prognostic factors of TMA after LDLT. Among 393 adult LDLT recipients, 30 patients (7.6%) were identified to have TMA. The 1-, 3- and 5-year survival rates of these patients were lower (60.6%, 52.5% and 47.7%, respectively) than those of patients without TMA (93.0%, 89.0% and 87.3%, respectively). Multivariate analysis confirmed that reduced administration of fresh frozen plasma and sensitization against HLA are closely related with TMA (odds ratio [OR]: 2.6 and 16.1, respectively). However, a review of the cases revealed that individual responses to treatment varied considerably and the main etiologies were difficult to determine. A comparison of the clinical factors suggested that late onset (>30 days), poor response to treatment and delayed diagnosis and/or treatment are associated with a poor outcome. Because the prevention of TMA in LDLT patients is difficult, early diagnosis and initiation of intensive therapies may be crucial to improve the prognosis.

[Hemolytic uremic syndrome in adults]

Hemolytic uremic syndrome (HUS) is related to a renal thrombotic microangiopathy, inducing hypertension and acute renal failure (ARF). Its pathogenesis involves an activation/lesion of microvascular endothelial cells, mainly in the renal vasculature, secondary to bacterial toxins, drugs, or autoantibodies. An overactivation of the complement alternate pathway secondary to a heterozygote deficiency of regulatory proteins (factor H, factor I or MCP) or to an activating mutation of factor B or C3 can also result in HUS. Less frequently, renal microthrombi are due to an acquired or a constitutional deficiency in ADAMTS-13, the protease cleaving von Wilebrand factor. Hemolytic anemia with schistocytes, thrombocytopenia without evidence of disseminated intravascular coagulation, and renal failure are consistently found. In typical HUS, a prodromal diarrhea, with blood in the stools, is observed, related to pathogenic enterobacteria, most frequently E. Coli O157:H7. HUS may also occur in the post partum period, and is then related to a factor H or factor I deficiency. HUS may also occur after various treatments such as mitomycin C, gemcitabine, ciclosporin A, or tacrolimus, and as reported more recently bevacizumab, an anti VEGF antibody. Atypical HUS are not associated with diarrhea, may be sporadic or familial, and can be related to an overactivation of the complement alternate pathway. More recently, some of them have been related to a mutation of thrombomodulin, which also regulates the alternate pathway of complement. In adults, several HUS are encountered in the course of chronic nephropathies: nephroangiosclerosis, chronic glomerulonephritis, post irradiation nephropathy, scleroderma, disseminated lupus erythematosus, antiphospholipid syndrome. Overall the prognosis of HUS has improved, with a patient survival greater than 85% at 1 year. Chronic renal failure is observed as a sequella in 20 to 65% of the cases. Plasma infusions and plasma exchanges are effective in most of the cases to treat hemolysis and thrombocytopenia. Steroid therapy is debated, as well as immunosuppressive drugs, including rituximab, in autoimmune forms. A new monoclonal anti-C5 antibody is tested, and seems to be effective in atypical HUS with abnormal complement alternate pathway activation. If terminal renal failure occurs, renal transplantation can be performed but the risk of recurrence, which very low in post infectious forms of HUS, is about 70 to 80% in genetic forms of complement regulatory protein deficiency.

The spectrum of thrombotic thrombocytopenic purpura: a clinicopathologic demonstration of tacrolimus-induced thrombotic thrombocytopenic purpura in a lung transplant patient

Immunosuppressive drugs used post-transplantation are among the most common causes of thrombotic thrombocytopenic purpura (TTP). Diagnosis is often confounded not only by its myriad presentations, but also because these manifestations may be explained by the comorbidities or complications of transplantation. A 61-year-old female who had a single lung transplant for severe chronic obstructive pulmonary disease maintained on corticosteroids, tacrolimus and mycophenolate mofetil, was admitted for fever, headache with confusion and lethargy. She was mildly anemic and thrombocytopenic. Peripheral smear showed rare fragmented red cells. Muddy brown casts were present on urinalysis. She was diagnosed with TTP. Tacrolimus was discontinued and the mental status of the patient, anemia and thrombocytopenia improved significantly.

Evidence based therapeutic apheresis in autoimmune and other hemolytic anemias

PURPOSE OF REVIEW

This article reviews recent publications that bear on the evidential basis for therapeutic apheresis in diseases in which hemolytic anemia is a prominent feature.

RECENT FINDINGS

Therapeutic plasma exchange continues to be reported sporadically in severe autoimmune hemolytic anemia, with inconsistent results. Autoimmune deficiency of ADAMTS13 has provided a compelling rationale for therapeutic plasma exchange in some patients with thrombotic thrombocytopenic purpura; conversely such deficiency is consistently absent in certain clinically similar syndromes for which therapeutic plasma exchange is not or may not be beneficial. Refinements in assays for ADAMTS13 should further clarify its role in idiopathic thrombotic thrombocytopenic purpura. Oral iron chelators have shown promise in recent trials in chronically transfused patients with sickle cell disease and may provide an alternative to red cell exchange to prevent iron overload.

SUMMARY

The proper role of therapeutic plasma exchange in the treatment of autoimmune hemolytic anemia remains uncertain. Therapeutic plasma exchange continues to be indicated for idiopathic thrombotic thrombocytopenic purpura regardless of ADAMTS13 levels, but more accessible and physiological ADAMTS13 assays may raise questions about the rationale for and value of plasma exchange in ADAMTS13 nondeficient patients. Oral iron chelation may obviate the need for red cell exchange as a means to prevent iron overload in chronically transfused patients with sickle cell disease.

Successful treatment of propafenone, digoxin and warfarin overdosage with plasma exchange therapy and rifampicin

We report here the successful treatment of a 16-year-old female who ingested 20 tablets of digoxin each containing 0.25 mg (total dose ingested equivalent to 0.1 mg/kg), 32 tablets of warfarin each containing 5mg (equivalent to 3.2 mg/kg), and approximately 15 tablets of propafenone each containing 300 mg (equivalent to 90 mg/kg). The patient developed hypotension and sinus bradycardia necessitating external cardiac pacing 17 hours after drug ingestion. In addition to gastric lavage, activated charcoal, blood alkalinisation, administration of vitamin K and temporary cardiac pacing, the authors performed plasma exchange for drug removal and administered rifampicin in order to increase the metabolism of digoxin, propafenone and warfarin. The patient was discharged without any sequelae. Plasma exchange may be lifesaving in drug ingestions where there is a low volume of distribution and high plasma protein binding. Rifampicin, an inducer of cytochrome p450, may be used in intoxications for elimination of drugs with inactive metabolites.

Thrombotic microangiopathies: an update

Thrombotic microangiopathies (TMA) are microvascular occlusive disorders characterized by hemolytic anemia caused by fragmentation of erythrocytes and thrombocytopenia due to increased platelet aggregation and thrombus formation, eventually leading to disturbed microcirculation with reduced organ perfusion. Although several disease states may manifest as TMA, the two most relevant conditions associated with TMA are thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), characterized by prominent brain or renal lesions, respectively. However, occasionally the clinical distinction between these two conditions can be difficult. In this review, we focus on the epidemiologic and diagnostic criteria as well as on the most recent insights into the pathophysiology and treatment of these two conditions.

Advances in the pathogenesis, diagnosis and treatment of thrombotic thrombocytopenic purpura and hemolytic uremic syndrome

The thrombotic microangiopathies are microvascular occlusive disorders characterized by hemolytic anemia caused by fragmentation of erythrocytes and thrombocytopenia due to increased platelet aggregation and thrombus formation, eventually leading to disturbed microcirculation with reduced organ perfusion. Depending on whether brain or renal lesions prevail, two different entities have been described: thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). However, not rarely the clinical distinctions between these two conditions remain questionable. Recent studies have contributed greatly to our current understanding of the molecular mechanisms leading to TTP and HUS. In this review, we briefly focus on the most important advances in the pathophysiology, diagnosis and treatment of these two thrombotic microangiopathies.

Successful plasma therapy for atypical hemolytic uremic syndrome caused by factor H deficiency owing to a novel mutation in the complement cofactor protein domain 15

Quantitative or functional deficiency of complement factor H results in uncontrolled complement activation. This leads to thrombotic microangiopathy and finally causes renal failure (atypical hemolytic uremic syndrome [aHUS]). By regular analysis of factor H in patients with aHUS, the authors found a complete factor H deficiency in an infant in whom aHUS developed at 8 months of age. Factor H was quantified by enzyme-linked immunosorbent assay and further analyzed by Western blot using a factor H-specific antibody. Complement activation was determined by measuring total hemolytic activity of the classical (CH50) and alternative (APH50) pathways, C3 and C3d. The sequence of factor H gene was determined. Serial factor H measurements after fresh frozen plasma infusion allowed calculation of a factor H half-life. Factor H was absent in plasma (<1 mug/mL), and the complement system was highly activated (CH50, APH50, C3 decreased; C3d increased). Genetic analysis identified a novel homozygous factor H mutation (T2770A; Y899Stop) in CCP domain 15, most likely causing defective protein secretion. Time course measurements of factor H after plasma infusion established a factor H half-life of about 6 days. By repetitive plasma infusions (20 mL/kg over about 2 to 3 hours) the authors were able to interrupt the vicious circle of thrombotic microangiopathy in a factor H-deficient patient with aHUS. Based on the measured factor H half-life of about 6 days, regular plasma infusions in 2-week intervals were given, which prevented further aHUS episodes and stopped the decline of kidney function.

Thrombotic microangiopathy in living-donor liver transplantation

BACKGROUND

Thrombotic microangiopathy (TMA) is a fatal complication characterized by microvascular occlusive disorder resulting in systemic or intrarenal platelet aggregation, severe thrombocytopenia, and microangiopathic hemolytic anemia. Only sporadic case reports of TMA after cadaveric or living-donor liver transplantation (LDLT) have been described.

METHODS

The authors report 10 (5% of the total series) TMA patients after LDLT and review the previously reported cases. TMA was diagnosed on the basis of progressive thrombocytopenia of unknown cause and microangiopathic hemolytic anemia, suggested by sharp elevation of serum lactate dehydrogenase levels and the presence of fractionated erythrocytes in blood smear.

RESULTS

Of the 10 patients with TMA, 7 presented with viral hepatitis (2 with hepatitis B and 5 with hepatitis C virus infection) as the cause of end-stage liver disease. Clinical diagnosis of TMA was made at a median interval of 18 days (range, 3-356 days) from the time of transplantation. Conversion of calcineurin inhibitors (CNI) was conducted in nine patients. One patient recovered after CNI conversion alone. Plasma exchange was performed in eight patients. Three patients died.

CONCLUSIONS

Immediate treatment of TMA should be initiated by reduction or conversion of CNI followed by plasma exchange. Hepatitis C virus infection might contribute to the high incidence of TMA in LDLT patients.

Two novel ADAMTS13 gene mutations in thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome (TTP/HUS)

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS) are now considered to be variants of one single syndrome called thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome (TTP/HUS). Key features are thrombocytopenia, hemolytic anemia, and subsequently impaired function of different organs, especially the kidneys and the central nervous system (CNS). One possible reason is the deficiency of von Willebrand factor-cleaving protease (vWF-CP) resulting in persistence of uncleaved, ultralarge von Willebrand factor multimers (ULvWFM).

METHODS

We report a patient who was initially diagnosed with Evans syndrome (hemolytic anemia and autoimmune thrombocytopenia) as infant. At 10 years of age he developed HUS-like disease with gastrointestinal tract infection, hemolytic anemia, thrombocytopenia,and acute renal failure. However, enteropathogenic Escherichia coli-like or Shiga-like toxins were not detected.

RESULTS

Further investigations revealed severe deficiency (<3%; normal >40%) of vWF-CP activity caused by compound heterozygosity of two novel ADAMTS13 gene mutations (1170 G>C [W390C] and 3735 G>A [W1245X]. vWF-CP autoantibodies were not detected. Periodic (every 2 weeks) treatment with fresh frozen plasma (FFP) maintained both platelet level and kidney function within normal range and prevented new episodes of TTP/HUS.

CONCLUSION

Enteropathogenic E. coli- and Shiga-like toxin-negative patients who present with hemolytic or thrombocytopenic episodes and HUS like symptoms should be tested for vWF-CP deficiency and other noninfectious reasons for TTP/HUS since plasma substitution possibly provides an efficient therapeutic option for this subgroup of patients.

Drug-induced thrombotic thrombocytopenic purpura/hemolytic uremic syndrome: a concise review

An extensive variety of drugs have been associated with thrombotic thrombocytopenic purpura and hemolytic uremic syndrome (TTP/HUS). Although a direct causal effect has usually not been proven, the cumulative evidence linking several drugs with TTP/HUS is strong. This paper reviews several categories of drugs including antineoplastics, immunotherapeutics and anti-platelet agents that have been reported to induce TTP/HUS. The pathogenesis of drug-induced TTP/HUS and the effectiveness of treatment regimens are also reviewed. A consensus on diagnostic criteria to accurately and consistently diagnose drug-induced TTP is needed.

Treatment of postpartum thrombotic microangiopathy with plasma exchange using cryosupernatant as replacement

Hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are rare but acknowledged problems of pregnancy and the postpartum period. These diseases together with thrombotic angiopathy are associated with high maternal and fetal mortality and severe long-term morbidity. We describe four women with postpartum HUS/TTP treated with plasma exchange cryosupernatant fraction of plasma (CFP) as replacement fluid. Anuria or oliguria at the beginning of treatment and thrombocytopenia [thromb- (29-68) x 109/L] were common features. Two of the patients developed a prolonged and more difficult clinical condition affecting the central nervous system and the liver and their platelet counts remained low despite the plasma exchange. The renal and hepatic function of all of the patients recovered fully. This small analysis lends weight to early plasma exchange with cryosupernatant as part of the treatment of postpartum HUS/TTP and suggests that persistent thrombocytopenia is a signal of more serious disease.

Von Willebrand factor--cleaving protease activity in thrombotic microangiopathy after living donor liver transplantation: a case report

Defective plasma activity of Von Willebrand factor (VWF)-cleaving protease (CP) and/or the inhibitors against this protease has been shown to have a pathological role in several forms of thrombotic microangiopathy (TMA). This report describes a patient for whom a diagnosis of TMA was made immediately after living donor liver transplantation. In this patient, activity of VWF-CP and its inhibitor were analyzed serially. At the onset of the disease, VWF-CP activity was quantified as 17%. Inhibitor against this protease was positive, with a titer of 0.6 Bethesda U/mL, and its inhibitory activity was quantified as 3.8 Bethesda U/mg immunoglobulin G. Laboratory parameters and clinical features were significantly improved after induction of plasma exchange (PE) with fresh frozen plasma and concurrent cessation of tacrolimus therapy. The inhibitors disappeared after one session of PE. However, VWF-CP activity after a transient increase and again decreased to subnormal levels after completion of PE. Nevertheless, this did not result in disease recurrence. In view of sustained VWF-CP activity at disease onset and the absence of definite correlations between levels of this protease and clinical features, abnormality of this enzyme system had no essential role in the pathogenesis of TMA in this case. Clinical findings suggest that TMA was tacrolimus-induced.

Renal transplantation in patients with hemolytic uremic syndrome: high rate of recurrence and increased incidence of acute rejections

BACKGROUND

The reported outcome of renal transplantation in patients with the hemolytic uremic syndrome (HUS) varies greatly, probably related to the diverse causes of HUS. In this single-center retrospective study, we have analyzed the recurrence rate, the incidence of acute rejections, and graft survival in patients suffering from adult-onset and childhood-onset HUS.

METHODS

The medical records of 35 patients with end-stage renal disease caused by HUS, who received 50 renal allografts, were reviewed. A definite recurrence of HUS was diagnosed if both clinical and histologic signs of thrombotic microangiopathy (TMA) were present in the absence of any endovasculitis. If there were signs of mild endovasculitis, a probable recurrence was diagnosed.

RESULTS

After first renal transplantation, 0 definite and 1 (6%) probable recurrence occurred in 18 patients with childhood-onset HUS, as opposed to 7 (41%) definite and 3 (18%) probable recurrences in 17 adult-onset HUS patients (odds ratio [OR], 13.4; 95% confidence interval [CI], 1.7-105.7). In the latter patients, early use of cyclosporine A increased the risk for recurrence. The incidence of acute rejections was increased compared with matched controls (OR, 1.52; 95% CI, 1.05-2.19 for adult-onset HUS and OR, 1.88; 95% CI, 1.34-2.62 for childhood-onset HUS). One-year graft survival in adult-onset HUS was poor (29%), whereas 1-year graft survival in childhood-onset HUS was comparable to matched controls.

CONCLUSIONS

In adult-onset HUS, the recurrence rate and the incidence of acute rejections are high, resulting in a detrimental graft survival. In childhood-onset HUS, the recurrence rate is low, but the posttransplantation course is complicated by an increased incidence of acute rejections.

Therapeutic plasma exchange in the intensive care setting

The potential to treat life-threatening conditions with therapeutic plasma exchange (TPE) is limited to a few situations. In severe pulmonary hemorrhage as a complication of several immune disorders (e.g., antiglomerular basement membrane antibody disease, Wegener's granulomatosus, lupus erythematosus), TPE should only be considered after conventional measures (mostly pulses of methylprednisolone) have been applied. Idiopathic familial and nonfamilial thrombotic thrombocytopenic purpura as well as the subset of the hemolytic uremic syndrome not associated with diarrhea are clear indications for TPE using fresh frozen plasma as replacement fluid. Patients with myasthenic crisis will also benefit from TPE and will improve within 1 day. Acute pancreatitis as a complication of the chylomicronemia syndrome has a poor prognosis and should be treated with TPE without any delay. In the case of drug overdose or intoxication, the efficiency of TPE to remove the offending drug is usually overestimated. In this situation, TPE is useful only when the plasma protein binding of the substance is high (>80%) and the volume of distribution is low (<0.2 L/kg body weight). TPE is not without risks and hazards (e.g., vascular access, bleeding, allergy), which should also be considered when discussing this extracorporeal therapy in otherwise refractory clinical conditions.

[Pathogenesis and clinical course of hereditary nephropathies]

Hereditary diseases have to be considered in the differential diagnosis of many kidney diseases. The kidney can be affected by systemic metabolic diseases such as primary hyperoxaluria or Fabry's disease. Inborn errors of the coagulation cascade or the complement system may cause familiar forms of the hemolytic uremic syndrome. Of central interest are hereditary cystic kidney diseases with autosomal dominant polycystic kidney disease as its most prominent example. Hereditary forms of the nephrotic syndrome are usually caused by abnormalities of podocyte function. Alport's syndrome is a classical example of a basement membrane disease. Of special interest are hereditary defects in tubular transport mechanisms such as carrier defects affecting sodium reabsorption along the tubulus.