Thrombotic thrombocytopenic purpura and the atypical hemolytic uremic syndrome: an update

Systemic Lupus Erythematosus (SLE) and Thrombotic Thrombocytopenic Purpura (TTP) Presenting as Recurrent Strokes: A Case Report

Thrombotic thrombocytopenic purpura (TTP) is a rare but potentially life-threatening condition characterized by fever, acute hemolysis, thrombocytopenia, renal dysfunction, and CNS dysfunction. A peripheral smear shows schistocytes because of microangiopathy. It is extremely rare for TTP and systemic lupus erythematosus (SLE) to coexist. This report details an Indian female patient's uncommon clinical presentation of TTP linked to SLE. A 52-year-old woman presented to the emergency department with complaints of altered sensorium and weakness of the right side of the body. She was initially evaluated as a case of a cerebrovascular accident. CT brain imaging revealed multiple ischemic infarcts involving both cerebral hemispheres. MRI brain confirmed the same. During further evaluation, she was found to have hemolytic anemia, thrombocytopenia, and nephrotic range proteinuria. Immunological investigations confirmed SLE. A peripheral smear revealed schistocytes, and the PLASMIC score confirmed a high risk of TTP. The patient was treated with immunosuppressants, plasma exchange, and hemodialysis, along with other supportive measures. The patient showed a positive response to the therapy mentioned, with improved power and renal function. The patient denied a renal biopsy and was discharged after two weeks. This case report emphasizes the importance of the association between TTP and SLE.

Viruses and thrombocytopenia

Thrombocytopenia, characterized by a decrease in platelet count, is a multifaceted clinical manifestation that can arise from various underlying causes. This review delves into the intriguing nexus between viruses and thrombocytopenia, shedding light on intricate pathophysiological mechanisms and highlighting the pivotal role of platelets in viral infections. The review further navigates the landscape of thrombocytopenia in relation to specific viruses, and sheds light on the diverse mechanisms through which hepatitis C virus (HCV), measles virus, parvovirus B19, and other viral agents contribute to platelet depletion. As we gain deeper insights into these interactions, we move closer to elucidating potential therapeutic avenues and preventive strategies for managing thrombocytopenia in the context of viral infections.

Trends of Coagulation Parameters in Human Immunodeficiency Virus Patients

Background and Objectives: HIV disease is recognized to cause inconsistencies in coagulation via various pathways during infection. Some studies have indicated that HIV-infected patients are prone to developing thrombocytopenia, thrombosis, or autoantibodies that may cause difficulties in diagnosis. This study is intended to measure the trend of coagulation parameters in Sudanese patients with HIV. Materials and Methods: A cross-sectional study was carried out in patients with HIV admitted to the Sudan National AIDS Program (SNAP) from January 2018 to December 2019. Prothrombin time (PT), partial thromboplastin time (PTT), thrombin time (TT), D-dimer (DD), hemoglobin (HB), total lymphocyte count (TLC), platelet count (PLT), and a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13), were evaluated among HIV Sudanese patients. Results: Out of the 44 HIV patients included, 6 (13.6%) were found to have thrombotic thrombocytopenic purpura-like events and 12 (27.2%) had antiphospholipid antibodies, of whom 8 (66.6%) showed anticardiolipin antibody (1gG (75%) and IgM (25%)) and 4 showed lupus anticoagulants. The HB, TLC, and PLT values were found to be significantly lower in HIV patients than in control (p = 0.000, 0.000, and 0.050, respectively). The PT and ADAMTS13 values showed no significant difference between HIV patients and control (p = 0.613 and 0.266, respectively). The PTT, TT, and DD values were found to be augmented in HIV patients versus the control (p = 0.000). Conclusions: Thrombotic thrombocytopenic purpura-like events among HIV Sudanese patients were explored. In addition, antiphospholipid antibodies were strikingly seen in these patients. Additional research is anticipated to confirm these diagnoses.

Rare Presentation of Atypical Hemolytic Uremic Syndrome in a Child With Acute Lymphocytic Leukemia and Pancreatitis

Atypical hemolytic uremic syndrome (aHUS) is associated with significant mortality and morbidity, including acute renal injury, anemia and thrombocytopenia. Rare cases of aHUS in a child with acute leukemia before diagnosis or during chemotherapy have been reported. We report a pediatric case of B-cell acute lymphoblastic leukemia complicated by pancreatitis with concomitant aHUS following induction chemotherapy.

Thrombotic Thrombocytopenic Purpura in Interferon Beta-1a-Treated Patient Diagnosed with Relapsing-Remitting Multiple Sclerosis: A Case Report

Background: Secondary thrombotic thrombocytopenic purpura (TTP) due to interferon beta-1a intramuscular (im) treatment is an uncommon adverse effect with only a few cases in multiple sclerosis patients reported worldwide. TTP together with haemolytic uremic syndrome (HUS) are classic forms of thrombotic microangiopathy, characterized by small-vessel platelet micro-thrombi that manifest clinically in a similar manner. Most common signs and symptoms include bruises and ecchymosis, neurologic symptoms and renal impairment. Interferon beta-1a represents one of the first-line therapies for relapsing-remitting multiple sclerosis due to its accessibility and efficacy. Case presentation: A 36-year-old woman who was previously diagnosed with relapsing-remitting multiple sclerosis had received weekly intramuscular injections with beta-interferon-1a (Avonex 30 mcg). After 9 months of treatment, she presented bruises and ecchymosis on her limbs and torso, epistaxis, gingival bleeding aggravated within 48 h and a persistent headache that was non-responsive to common analgesics. Haematology tests revealed typical results for thrombotic microangiopathy, including severe thrombocytopenia (4000/mm³) and microangiopathic haemolytic anaemia with frequent schistocytes on the peripheral blood smear. Once the beta-interferon administration was ceased and upon the initiation of methylprednisolone, the symptoms remitted. Conclusions: In this case study, we portrayed the particular association between the remission phase of multiple sclerosis and the violent onset of interferon-induced thrombotic thrombocytopenic purpura.

Genomic investigation of inherited thrombotic microangiopathy-aHUS and TTP

Thrombotic microangiopathies (TMA) are a heterogeneous group of red cell fragmentation syndromes characterized by a tendency for thrombosis and pathognomonic red cell fragments in peripheral blood, which results in thrombosis in the microvasculature due to endothelial damage. Genomic investigations into inherited TMAs are of diagnostic, prognostic and therapeutic value. Here, we present two cases that capture the importance of performing genomic testing in rare disorders. Treatment options for these conditions, such as plasma exchange and monoclonal antibodies against complement factors, are intensive and expensive health care interventions. The results of genomic investigation into rare TMAs can better inform the clinicians and their patients of prognosis and suitable personalized treatment options.

ISTH guidelines for the diagnosis of thrombotic thrombocytopenic purpura

BACKGROUND

Despite an increase in our understandings of pathogenesis of thrombotic thrombocytopenic purpura (TTP), the approaches for initial diagnosis and management of TTP vary significantly.

OBJECTIVE

The evidence-based guidelines of the International Society on Thrombosis and Haemostasis (ISTH) are intended to support patients, clinicians, and other health care professionals in their decisions about the initial diagnosis and management of acute TTP.

METHODS

In June 2018, ISTH formed a multidisciplinary panel that included hematologists, an intensive care physician, nephrologist, clinical pathologist, biostatistician, and patient representatives, as well as a methodology team from McMaster University. The panel composition was designed to minimize the potential conflicts of interests. The panel used the Grading of Recommendations Assessment, Development, and Evaluation approach and the Population, Intervention, Comparison, Outcome framework to develop and grade their recommendations. Public comments were sought and incorporated in the final document.

RESULTS

The panel agreed on three recommendations covering the initial diagnosis with emphasis on the importance of ADAMTS13 testing (eg, activity, anti-ADAMTS13 IgG or inhibitor) and assessment of the pretest probability of TTP by clinical assessment and/or the risk assessment models like the PLASMIC or French score. The panel noted how availability and turnaround time of ADAMTS13 test results might affect early diagnosis and management, in particular the use of caplacizumab.

CONCLUSIONS

There is a lack of high-quality evidence to support strong recommendations for the initial diagnosis and management of a suspected TTP. The panel emphasized the importance of obtaining ADAMTS13 testing in a proper clinical context. Future research should focus on how to monitor and act on ADAMTS13 levels during remission.

Differential contribution of C5aR and C5b-9 pathways to renal thrombic microangiopathy and macrovascular thrombosis in mice carrying an atypical hemolytic syndrome-related factor H mutation

Atypical hemolytic uremic syndrome (aHUS) is a form of thrombotic microangiopathy (TMA) caused by dysregulated complement activation. Clinically, aHUS is effectively treated by an anti-C5 monoclonal antibody (mAb) but whether the disease is mediated by the C5a receptor (C5aR) or C5b-9 pathway, or both, is unknown. Here we address this in a factor H mutant mouse (FH^R/R) which developed complement-mediated TMA as well as macrovascular thrombosis caused by an aHUS-related factor H point mutation (mouse W1206R, corresponding to human W1183R). C5 deficiency and anti-C5 mAb treatment blocked all disease manifestations in FH^R/R mice. C5aR1 gene deficiency prevented macrovascular thrombosis in various organs but did not improve survival or reduce renal TMA. Conversely, C6 or C9 deficiency significantly improved survival and markedly diminished renal TMA but did not prevent macrovascular thrombosis. Interestingly, as they aged both FH^R/R C6^-/- and FH^R/R C9^-/- mice developed glomerular disease reminiscent of C3 glomerulonephritis. Thus, C5aR and C5b-9 pathways drove different aspects of disease in FH^R/R mice with the C5aR pathway being responsible for macrovascular thrombosis and chronic inflammatory injury while the C5b-9 pathway caused renal TMA. Our data provide new understanding of the pathogenesis of complement-mediated TMA and macrovascular thrombosis in FH^R/R mice and suggest that C5 blockade is more effective for the treatment of aHUS than selectively targeting the C5aR or C5b-9 pathway alone.

Atypical Thrombotic Thrombocytopenic Purpura Presenting as Stroke

Here we report a case of atypical thrombotic thrombocytopenic purpura that presented as an ischemic cerebrovascular accident. A 56-year-old man with multiple cardiovascular risk factors presented with sudden left-sided weakness, slurred speech, and left facial droop. He showed mild improvement when he was treated with thrombolytic therapy according to the hospital stroke protocol. Later in the course, he developed thrombocytopenia followed by schistocytes revealed by peripheral blood smear and other lab abnormalities. Thrombotic thrombocytopenic purpura (TTP) was suspected, and he was treated with total plasma exchange that improved his condition significantly. This case shows that TTP can have unusual and atypical presentations either with the first episode or upon relapse, making diagnosis extremely difficult. Because patients may not present the expected clinical findings, it is important to be aware of variant presentations. In the early stages of the disease, platelet aggregation and thrombus formation may not be widespread, and thrombocytopenia and microangiopathic hemolytic anemia may not be clinically evident. Patients can present soon after the onset of symptoms when the typical laboratory abnormalities may not have had ample time to manifest. Although most other similar cases in the literature had a previous typical presentation of the disease before an atypical presentation, our patient's first presentation was atypical. An atypical presentation of disease in a patient with cardiovascular risk factors may therefore be extremely difficult to diagnose. We believe that TTP should be considered for any patient presenting with stroke and thrombocytopenia.

Blocking Properdin Prevents Complement-Mediated Hemolytic Uremic Syndrome and Systemic Thrombophilia

Background Properdin (P) is a positive regulator of the alternative pathway of complement activation. Although P inhibition is expected and has been shown to ameliorate the alternative pathway of complement-mediated tissue injury in several disease models, it unexpectedly exacerbated renal injury in a murine model of C3 glomerulopathy. The role of P in atypical hemolytic uremic syndrome (aHUS) is uncertain.Methods We blocked P function by genetic deletion or mAb-mediated inhibition in mice carrying a factor H (FH) point mutation, W1206R (FH^R/R), that causes aHUS and systemic thrombophilia with high mortality.Results P deficiency completely rescued FH^R/R mice from premature death and prevented thrombocytopenia, hemolytic anemia, and renal disease. It also eliminated macrovessel thrombi that were prevalent in FH^R/R mice. All mice that received a function-blocking anti-P mAb for 8 weeks survived the experimental period and appeared grossly healthy. Platelet counts and hemoglobin levels were significantly improved in FH^R/R mice after 4 weeks of anti-P mAb treatment. One half of the FH^R/R mice treated with an isotype control mAb but none of the anti-P mAb-treated mice developed stroke-related neurologic disease. Anti-P mAb-treated FH^R/R mice showed largely normal renal histology, and residual liver thrombi were detected in only three of 15 treated mice.Conclusions These results contrast with the detrimental effect of P inhibition observed in a murine model of C3 glomerulopathy and suggest that P contributes critically to aHUS pathogenesis. Inhibition of P in aHUS may be of therapeutic benefit.

Acute kidney injury in a patient with hemolytic anemia and thrombocytopenia

Atypical hemolytic uremic syndrome (HUS) is clinically difficult to distinguish from HUS and thrombotic thrombocytopenic purpura. Atypical HUS results from dysregulation of complement activation causing thrombotic microangiopathy affecting multiple organ systems. Atypical HUS is associated with high morbidity and mortality, making early recognition and appropriate therapy necessary to improve patient outcomes.

Case Series of 3 Patients Diagnosed With Atypical Hemolytic Uremic Syndrome Successfully Treated With Steroids, Plasmapheresis, and Rituximab

Rationale

Atypical hemolytic uremic syndrome, which has a high probability of chronic kidney disease, morbidity, and mortality, needs to be promptly recognized when patients present with microangiopathic hemolysis.

Presenting Concerns of the Patient

Three patients present with laboratory parameters consistent with a thrombotic microangiopathy. With a suspected diagnosis of thrombotic thrombocytopenic purpura, steroids with plasmapheresis were initiated.

Diagnoses

With ADAMTS13 levels reported normal, the suspected diagnoses were reevaluated. Given ongoing renal impairment, atypical hemolytic uremic syndrome was strongly considered.

Interventions

When local funding issues precluded the prompt use of eculizumab, 4 doses of weekly rituximab were trialed.

Outcome

Over 2 years later, all 3 patients have sustained durable remissions defined by the absence of kidney impairment or laboratory investigations concerning for microangiopathic hemolytic relapse.

Lessons Learned

In cases of a suspected autoimmune mechanism leading to atypical hemolytic uremic syndrome, long-term use of eculizumab may not be required.

Influenza-associated thrombotic microangiopathies

Thrombotic microangiopathy (TMA) refers to phenotypically similar disorders, including hemolytic uremic syndromes (HUS) and thrombotic thrombocytopenic purpura (TTP). This review explores the role of the influenza virus as trigger of HUS or TTP. We conducted a literature survey in PubMed and Google Scholar using HUS, TTP, TMA, and influenza as keywords, and extracted and analyzed reported epidemiological and clinical data. We identified 25 cases of influenza-associated TMA. Five additional cases were linked to influenza vaccination and analyzed separately. Influenza A was found in 83%, 10 out of 25 during the 2009 A(H1N1) pandemic. Two patients had bona fide TTP with ADAMTS13 activity <10%. Median age was 15 years (range 0.5-68 years), two thirds were male. Oligoanuria was documented in 81% and neurological involvement in 40% of patients. Serum C3 was reduced in 5 out of 14 patients (36%); Coombs test was negative in 7 out of 7 and elevated fibrin/fibrinogen degradation products were documented in 6 out of 8 patients. Pathogenic complement gene mutations were found in 7 out of 8 patients tested (C3, MCP, or MCP combined with CFB or clusterin). Twenty out of 24 patients recovered completely, but 3 died (12%). Ten of the surviving patients underwent plasma exchange (PLEX) therapy, 5 plasma infusions. Influenza-mediated HUS or TTP is rare. A sizable proportion of tested patients demonstrated mutations associated with alternative pathway of complement dysregulation that was uncovered by this infection. Further research is warranted targeting the roles of viral neuraminidase, enhanced virus-induced complement activation and/or ADAMTS13 antibodies, and rational treatment approaches.

Expert Statements on the Standard of Care in Critically Ill Adult Patients With Atypical Hemolytic Uremic Syndrome

A typical hemolytic uremic syndrome (aHUS) presents similarly to thrombotic thrombocytopenic purpura (TTP) and other causes or conditions with thrombotic microangiopathy (TMA), such as disseminated intravascular coagulation or sepsis. Similarity in clinical presentation may hinder diagnosis and optimal treatment selection in the urgent setting in the ICU. However, there is currently no consensus on the diagnosis or treatment of aHUS for ICU specialists. This review aims to summarize available data on the diagnosis and treatment strategies of aHUS in the ICU to enhance the understanding of aHUS diagnosis and outcomes in patients managed in the ICU. To this end, a review of the recent literature (January 2009-March 2016) was performed to select the most relevant articles for ICU physicians. Based on the paucity of adult aHUS cases overall and within the ICU, no specific recommendations could be formally graded for the critical care setting. However, we recognize a core set of skills required by intensivists for diagnosing and managing patients with aHUS: recognizing thrombotic microangiopathies, differentiating aHUS from related conditions, recognizing involvement of other organ systems, understanding the pathophysiology of aHUS, knowing the diagnostic workup and relevant outcomes in critically ill patients with aHUS, and knowing the standard of care for patients with aHUS based on available data and guidelines. In conclusion, managing critically ill patients with aHUS requires basic skills that, in the absence of sufficient data from patients treated within the ICU, can be gleaned from an increasingly relevant literature outside the ICU. More data on critically ill patients with aHUS are needed to validate these conclusions within the ICU setting.

Kidney Diseases Associated With Alternative Complement Pathway Dysregulation and Potential Treatment Options

Atypical hemolytic uremic syndrome and C3 glomerulopathy (dense deposit disease and C3 glomerulonephritis) are characterized as inappropriate activation of the alternative complement pathway. Genetic mutations affecting the alternative complement pathway regulating proteins (complement factor H, I, membrane cofactor protein and complement factor H-related proteins) and triggers (such as infection, surgery, pregnancy and autoimmune disease flares) result in the clinical manifestation of these diseases. A decade ago, prognosis of these disease states was quite poor, with most patients developing end-stage renal disease. Furthermore, renal transplantation in these conditions was associated with poor outcomes due to graft loss to recurrent disease. Recent advances in targeted complement inhibitor therapy resulted in significant improvement in disease remission, renal recovery, health-related quality of life and allograft survival.

Murine systemic thrombophilia and hemolytic uremic syndrome from a factor H point mutation

Complement plays a key role in host defense, but its dysregulation can cause autologous tissue injury. Complement activation is normally controlled by regulatory proteins, including factor H (FH) in plasma and membrane cofactor protein (MCP) on the cell surface. Mutations in FH and MCP are linked to atypical hemolytic uremic syndrome, a type of thrombotic microangiopathy (TMA) that causes renal failure. We describe here that disruption of FH function on the cell surface can also lead to disseminated complement-dependent macrovascular thrombosis. By gene targeting, we introduced a point mutation (W1206R) into murine FH that impaired its interaction with host cells but did not affect its plasma complement-regulating activity. Homozygous mutant mice carrying this mutation developed renal TMA as well as systemic thrombophilia involving large blood vessels in multiple organs, including liver, lung, spleen, and kidney. Approximately 30% of mutant mice displayed symptoms of stroke and ischemic retinopathy, and 48% died prematurely. Genetic deficiency of complement C3 and factor D prevented both the systemic thrombophilia and renal TMA phenotypes. These results demonstrate a causal relationship between complement dysregulation and systemic angiopathy and suggest that complement activation may contribute to various human thrombotic disorders involving both the micro- and macrovasculature.

Clinical Practice Guidelines for the Management of Atypical Hemolytic Uremic Syndrome in Korea

Atypical hemolytic uremic syndrome (aHUS) is a rare syndrome characterized by micro-angiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. The major pathogenesis of aHUS involves dysregulation of the complement system. Eculizumab, which blocks complement C5 activation, has recently been proven as an effective agent. Delayed diagnosis and treatment of aHUS can cause death or end-stage renal disease. Therefore, a diagnosis that differentiates aHUS from other forms of thrombotic microangiopathy is very important for appropriate management. These guidelines aim to offer recommendations for the diagnosis and treatment of patients with aHUS in Korea. The guidelines have largely been adopted from the current guidelines due to the lack of evidence concerning the Korean population.

Postinfectious Hemolytic Uremic Syndrome

Post-infectious hemolytic uremic syndrome (HUS) is caused by specific pathogens in patients with no identifiable HUS-associated genetic mutation or autoantibody. The majority of episodes is due to infections by Shiga toxin (Stx) producing Escherichia coli (STEC). This chapter reviews the epidemiology and pathogenesis of STEC-HUS, including bacterial-derived factors and host responses. STEC disease is characterized by hematological (microangiopathic hemolytic anemia), renal (acute kidney injury) and extrarenal organ involvement. Clinicians should always strive for an etiological diagnosis through the microbiological or molecular identification of Stx-producing bacteria and Stx or, if negative, serological assays. Treatment of STEC-HUS is supportive; more investigations are needed to evaluate the efficacy of putative preventive and therapeutic measures, such as non-phage-inducing antibiotics, volume expansion and anti-complement agents. The outcome of STEC-HUS is generally favorable, but chronic kidney disease, permanent extrarenal, mainly cerebral complication and death (in less than 5 %) occur and long-term follow-up is recommended. The remainder of this chapter highlights rarer forms of (post-infectious) HUS due to S. dysenteriae, S. pneumoniae, influenza A and HIV and discusses potential interactions between these pathogens and the complement system.

Role of the skin biopsy in the diagnosis of atypical hemolytic uremic syndrome

INTRODUCTION

Atypical hemolytic uremic syndrome (aHUS) is a prototypic thrombotic microangiopathy attributable to complement dysregulation. In the absence of complement inhibition, progressive clinical deterioration occurs. The authors postulated that a biopsy of normal skin could corroborate the diagnosis of aHUS through the demonstration of vascular deposits of C5b-9.

MATERIALS AND METHODS

Biopsies of normal skin from 22 patients with and without aHUS were processed for routine light microscopy and immunofluorescent studies. An assessment was made for vascular C5b-9 deposition immunohistochemically and by immunofluorescence. The biopsies were obtained primarily from the forearm and/or deltoid.

RESULTS

Patients with classic features of aHUS showed insidious microvascular changes including loose luminal platelet thrombi, except in 2 patients in whom a striking thrombogenic vasculopathy was apparent in biopsied digital ulcers. Extensive microvascular deposits of the membrane attack complex/C5b-9 were identified, excluding 1 patient in whom eculizumab was initiated before biopsy. In 5 of the 7 patients where follow-up was available, the patients exhibited an excellent treatment response to eculizumab. Patients without diagnostic clinical features of aHUS failed to show significant vascular deposits of complement, except 2 patients with thrombotic thrombocytopenic purpura including 1 in whom a Factor H mutation was identified.

CONCLUSIONS

In a clinical setting where aHUS is an important diagnostic consideration, extensive microvascular deposition of C5b-9 supports the diagnosis of either aHUS or a subset of thrombotic thrombocytopenic purpura patients with concomitant complement dysregulation; significant vascular C5b-9 deposition predicts clinical responsiveness to eculizumab.

Successful treatment of relapsing autoimmune thrombotic thrombocytopenic purpura with rituximab

Thrombotic thrombocytopenic purpura (TTP) is a rare but life-threatening condition characterized by thrombotic microangiopathy. The standard treatment for TTP is plasmapheresis. For refractory or relapsing cases, various immunosuppressive agents have been tried, and among them rituximab has shown promising results. TTP is rarer in the pediatric age group and the use of rituximab in children with TTP is limited. Reported herein is the successful treatment of relapsing autoimmune TTP with rituximab in a 12-year-old girl.

Eculizumab therapy leads to rapid resolution of thrombocytopenia in atypical hemolytic uremic syndrome

Eculizumab is highly effective in controlling complement activation in patients with the atypical hemolytic uremic syndrome (aHUS). However, the course of responses to the treatment is not well understood. We reviewed the responses to eculizumab therapy for aHUS. The results show that, in patients with aHUS, eculizumab therapy, when not accompanied with concurrent plasma exchange therapy, led to steady increase in the platelet count and improvement in extra-renal complications within 3 days. By day 7, the platelet count was normal in 15 of 17 cases. The resolution of hemolytic anemia and improvement in renal function were less predictable and were not apparent for weeks to months in two patients. The swift response in the platelet counts was only observed in one of five cases who received concurrent plasma exchange therapy and was not observed in a case of TMA due to gemcitabine/carboplatin. In summary, eculizumab leads to rapid increase in the platelet counts and resolution of extrarenal symptoms in patients with aHUS. Concurrent plasma exchange greatly impedes the response of aHUS to eculizumab therapy. Eculizumab is ineffective for gemcitabine/carboplatin associated TMA.

Atypical Hemolytic Uremic Syndrome: Differential Diagnosis from TTP/HUS and Management

Atypical hemolytic uremic syndrome (aHUS) is a rare form of thrombotic microangiopathy (TMA). It has an unfavorable outcome with death rates as high as 25% during the acute phase and up to 50% of cases progressing to end-stage renal failure. Uncontrolled complement activation through the alternative pathway is thought to be the main underlying pathopysiology of aHUS and corresponds to all the deleterious findings of the disease. Thrombotic thrombocytopenic purpura (TTP) and Shiga toxin-associated HUS are the 2 other important TMA diseases. Although differentiating HUS from TTP is relatively easy in children with a preceding diarrheal illness or invasive S. pneumoniae, differentiating aHUS from TTP or other microangiopathic disorders can present a major diagnostic challenge in adults. ADAMTS13 analysis is currently the most informative diagnostic test for differentiating TTP, congenital TTP, and aHUS. Today empiric plasma therapy still is recommended by expert opinion to be used as early as possible in any patient with symptoms of aHUS. The overall treatment goal remains restoration of a physiological balance between activation and control of the alternative complement pathway. So it is a reasonable approach to block the terminal complement complex with eculizumab in order to prevent further organ injury and increase the likelihood organ recovery. Persistence of hemolysis or lack of improvement of renal function after 3-5 daily plasmaphereses have to be regarded as the major criteria for uncontrolled TMA even if platelet count has normalized and as an indication to switch the treatment to eculizumab. Eculizumab has changed the future perspectives of patients with aHUS and both the FDA and the EMA have approved it as life-long treatment. However, there are still some unresolved issues about the follow-up such as the optimal duration of eculizumab treatment and whether it can be stopped or how to stop the therapy.