Hemolytic uremic syndrome associated with novel influenza A H1N1 infection

Influenza-induced thrombotic microangiopathy in a patient with cancer on proteasome inhibitor: a diagnostic dilemma

Thrombotic microangiopathy (TMA) in a cancer patient is a common complication of either cancer itself or anticancer therapy. Incidence of TMA from anticancer therapy was found to be > 15%, since the introduction of anti-angiogenic drugs like anti-vascular endothelial growth factor agents. It is, however, important to not ignore other causes of TMA such as bacteria, viruses, antiplatelet drugs, hereditary complement mutations, and autoimmune disorders. We present such a diagnostic dilemma in our patient who was admitted with influenza and was found to have TMA on renal biopsy, while on proteasome inhibitor (PI) therapy. With this case, we would like to highlight the importance of understanding the true cause of TMA to avoid unwarranted long-term discontinuation of life saving anti-cancer drugs after TMA resolution.

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.

Occurrence of atypical HUS associated with influenza B

Hemolytic uremic syndrome (HUS) is a disease characterized by thrombotic microangiopathy with a triad of non-immune hemolytic anemia, thrombocytopenia, and renal impairment. Approximately 10% of cases of HUS are classified as atypical (aHUS). While today many genetically forms of aHUS pathology are known, only about 50% of carriers precipitate the disease. The reason remains unclear, and triggering events like intercurrent infections have been postulated. In rare cases, influenza A is the known trigger of aHUS; however, no cases of influenza B have been reported.

CONCLUSION

We describe for the first time that influenza B strain as a trigger for aHUS in children with primary hereditary forms. We also showed in our three cases that immunization appears to be safe; however, this needs to be confirmed in a larger cohort. What is Known: • Known triggers of aHUS are infectious specimen. • Influenza A-associated aHUS cases are rarely published. What is New: • aHUS can be triggered by influenza B virus infection. • Influenza vaccination of patients with aHUS appears safe.

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.

Renal complications of seasonal and pandemic influenza A virus infections

Renal complications of influenza A virus infections are uncommon but can contribute to a deterioration in the patient's condition, which include acute kidney injury (AKI) in critically ill patients, rhabdomyolysis, hemolytic uremic syndrome (HUS), acute glomerulonephritis (AGN), disseminated intravascular coagulation (DIC), Goodpasture's syndrome, and acute tubulointerstitial nephritis (TIN). The clinical characteristics of AKI in critically ill patients with pandemic influenza A(H1N1) 2009 virus (A(H1N1)pdm09) infection are similar to uninfected patients. Underlying conditions associated with AKI include older age, diabetes mellitus, obesity, pregnancy, history of asthma, and chronic kidney disease. Histologic examination of the kidneys from patients with A(H1N1)pdm09 infection who died include acute tubular necrosis (ATN), myoglobin pigment, and DIC. A(H1N1)pdm09 is present in the kidneys of some patients. The clinical characteristics of patients with rhabdomyolysis associated with influenza A include younger age and the frequent occurrence of muscle symptoms. AKI occurs in approximately one third of patients with rhabdomyolysis due to influenza A. HUS is associated with A(H1N1)pdm09 as follows: Streptococcus pneumoniae-associated HUS following A(H1N1)pdm09 infection, HUS triggered by A(H1N1)pdm09 in patients with genetic complement dysregulation, and HUS associated with A(H1N1)pdm09 without known underlying disorder. AGN, Goodpasture's syndrome, and acute TIN are extremely rare complications of influenza A virus infection. Although the pathogenesis underlying renal injuries due to influenza A virus has not been delineated, some hypotheses have been advanced, including ATN due to renal hypoperfusion or rhabdomyolysis, glomerular microthrombosis due to DIC, direct viral injury to the kidney, and an altered immune system with systemic mononuclear cell activation following influenza A virus infections.

Management of hemolytic uremic syndrome

2011 has been a special year for hemolytic uremic syndrome (HUS): on the one hand, the dramatic epidemic of Shiga toxin producing E. coli -associated HUS in Germany brought the disease to the attention of the general population, on the other hand it has been the year when eculizumab, the first complement blocker available for clinical practice, was demonstrated as the potential new standard of care for atypical HUS. Here we review the therapeutic options presently available for the various forms of hemolytic uremic syndrome and show how recent knowledge has changed the therapeutic approach and prognosis of atypical HUS.

Viral-associated thrombotic microangiopathies

Thrombotic microangiopathies encompass a group of disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia associated with hyaline thrombi (comprised primarily of platelet aggregates in the microcirculation), and varying degrees of end-organ failure. Many primary (genetic) and secondary etiological predisposing factors have been described-namely pregnancy, autoimmune disorders, cancer, drugs and antineoplastic therapy, bone marrow transplantation/solid organ transplantation, and infections. In the setting of infectious diseases, the association with Shiga or Shiga-like exotoxin of Escherichia coli 0157:h7 or Shigella dysenteriae type 1-induced typical hemolytic uremic syndrome is well known. Recently however, an increasing body of evidence suggests that viruses may also play an important role as trigger factors in the pathogenesis of thrombotic microangiopathies. This is a comprehensive review focusing on the current understanding of viral associated/induced endothelial stimulation and damage that ultimately leads to the development of this life-threatening multisystemic disorder.

Pandemic H1N1 influenza A viral infection complicated by atypical hemolytic uremic syndrome and diffuse alveolar hemorrhage

We report here on a case of a 27-year-old man with atypical hemolytic uremic syndrome and diffuse alveolar hemorrhage associated with influenza A H1N1 infection. Treatment with oseltamivir, plasma exchange and hemodiafiltration for the hemolytic uremic syndrome and meticulous supportive care with steroid pulse therapy for the pulmonary alveolar hemorrhage was successful in this case. We discuss the relationship between hemolytic uremic syndrome and influenza A and the underlying immunologic factors that should be tested in a patient with atypical hemolytic uremic syndrome. We also discuss using steroid therapy for patients with H1N1-related diffuse alveolar hemorrhage.

Is complement a culprit in infection-induced forms of haemolytic uraemic syndrome?

Haemolytic uraemic syndrome (HUS) accounts for the most common cause of childhood acute renal failure. Characterized by the classical triad of a microangiopathic haemolytic anaemia, thrombocytopaenia and acute renal failure, HUS occurs as a result of Shiga-toxin producing microbes in 90% of cases. The remaining 10% of cases represent a heterogeneous subgroup in which inherited and acquired forms of complement dysregulation have been described in up to 60%. Emerging evidence suggests that microbes associated with HUS exhibit interaction with the complement system. With the advent of improved genetic diagnosis, it is likely that certain cases of infection-induced HUS may be attributed to underlying defects in complement components. This review summarises the interplay between complement and infection in the pathogenesis of HUS.

Pandemic H1N1 influenza A infection and (atypical) HUS--more than just another trigger?

Atypical hemolytic uremic syndrome (aHUS) is caused by mutations resulting in an exceedingly active alternative complement pathway. While today more than half a dozen genes are involved in aHUS pathology, only about 50% of carriers precipitate the disease. The reason for this phenomenon remains unclear, and triggering events like intercurrent infections have been postulated. In this context, reports on the development of (a)HUS in patients concomitantly diagnosed with pandemic H1N1 influenza A (pH1N1) infection are of great interest. They establish--for the first time in the literature--the link between aHUS and pH1N1 infection. While illnesses associated with pH1N1 infections during the recent pandemics were generally mild, secondary bacterial infections (e.g. Streptococcus pneumoniae) are known in patients with influenza A infections to not only aggravate the disease course, but also serve as a possible HUS trigger. Assuming pH1N1 was the cause of HUS in the cases reported here, it remains an interesting but unanswered hypothesis whether an underlying complement defect served as a susceptibility factor, at least in a subgroup of patients. In the future, pH1N1, but also pH1N1-associated, bacterial infections will have to be considered in (a)HUS patients, and further studies will be required to examine the role of the complement system in this condition.