Advances and challenges in the management of complement-mediated thrombotic microangiopathies

Complement-Mediated Thrombotic Microangiopathy Associated with Lupus Nephritis Treated with Eculizumab: A Case Report

Thrombotic microangiopathies (TMAs) involve multiple organ systems due to the presence of microangiopathic hemolysis. One such condition, atypical hemolytic uremic syndrome (aHUS), is a complement-mediated process that is part of a spectrum of disorders that have underlying complement dysfunction of the alternative pathway due to overactivity or decreased self-nonself discrimination by innate immunity. Complement-amplifying conditions such as pregnancy may unmask a diagnosis of aHUS. We present an important case of a pregnant 23-year-old Hispanic female who presented in mid-gestation (21 weeks) with an initial diagnosis of systemic lupus erythematosus (SLE) complicated by aHUS. She met clinical criteria for aHUS on presentation and was found to have a pathogenic CFHR1–3 homozygous deletion. She has been treated with intravenous and oral steroids, cyclophosphamide, subsequently also with plasma exchange, and finally with eculizumab with partial improvement in renal function. This case adds to the emerging literature showing that SLE and aHUS (or complement-mediated TMA) can be successfully treated with C5 blockade.

Therapeutic Plasma Exchange in Renal Disorders

Nephrologists use hemodialysis and hemofiltration to remove low molecular weight toxic constituents, and increasingly deploy therapeutic plasma exchange (TPE)/plasmapheresis to eliminate higher molecular weight substances such as immunoglobulins or immune complexes from plasma. This review discusses different modalities of TPE, their application in renal disorders, its rationale and complications. TPE is recommended based on evidence, in alloantibody-mediated diseases such as humoral antibody mediated renal transplant rejection, autoantibody mediated glomerulonephritis (GN) disorders for example, anti-glomerular basement membrane GN, as well as in antineutrophil cytoplasmic antibody mediated GN and antibody mediated thrombotic thrombocytopenic purpura. In many other renal illnesses, the rational use of TPE is gaining currency. Double membrane filtration, immune adsorption and cryofiltration are important modifications in TPE

Genetic Susceptibility to Postdiarrheal Hemolytic-Uremic Syndrome After Shiga Toxin-Producing Escherichia coli Infection: A Centers for Disease Control and Prevention FoodNet Study

Background

Postdiarrheal hemolytic-uremic syndrome (D+HUS) following Shiga toxin-producing Escherichia coli (STEC) infection is a serious condition lacking specific treatment. Host immune dysregulation and genetic susceptibility to complement hyperactivation are implicated in non-STEC-related HUS. However, genetic susceptibility to D+HUS remains largely uncharacterized.

Methods

Patients with culture-confirmed STEC diarrhea, identified through the Centers for Disease Control and Prevention FoodNet surveillance system (2007-2012), were serotyped and classified by laboratory and/or clinical criteria as having suspected, probable, or confirmed D+HUS or as controls and underwent genotyping at 200 loci linked to nondiarrheal HUS or similar pathologies. Genetic associations with D+HUS were explored by multivariable regression, with adjustment for known risk factors.

Results

Of 641 enrollees with STEC O157:H7, 80 had suspected D+HUS (41 with probable and 32 with confirmed D+HUS). Twelve genes related to cytokine signaling, complement pathways, platelet function, pathogen recognition, iron transport, and endothelial function were associated with D+HUS in multivariable-adjusted analyses (P ≤ .05). Of 12 significant single-nucleotide polymorphisms (SNPs), 5 were associated with all levels of D+HUS (intergenic SNP rs10874639, TFRC rs3804141, EDN1 rs5370, GP1BA rs121908064, and B2M rs16966334), and 7 SNPs (6 non-complement related) were associated with confirmed D+HUS (all P < .05).

Conclusions

Polymorphisms in many non-complement-related genes may contribute to D+HUS susceptibility. These results require replication, but they suggest novel therapeutic targets in patients with D+HUS.

Plasma exchange in thrombotic microangiopathies (TMAs) other than thrombotic thrombocytopenic purpura (TTP)

Thrombotic microangiopathies (TMAs) are a diverse group of disorders that are characterized by common clinical and laboratory features. The most commonly thought-of TMA is thrombotic thrombocytopenic purpura (TTP). Because of the marked improvement in patient mortality associated with the use of therapeutic plasma exchange (TPE) in TTP, this therapy has been applied to all of the TMAs. The issue, however, is that the pathophysiology varies and in many instances may represent a disorder of the endothelium and not the blood; in some cases, the pathophysiology is unknown. The use of TPE is further obscured by a lack of strong supporting literature on its use, with most consisting of case series and case reports; controlled or randomized controlled trials are lacking. Evidence supporting the use of TPE in the treatment of TMAs (other than TTP and TMA-complement mediated) is lacking, and therefore its role is uncertain. With the greater availability of genetic testing for mutations involving complement regulatory genes and complement pathway components, there seems to be a percentage of TMA cases, other than TMA-complement mediated, in which complement pathway mutations are involved in some patients. The ability of TPE to remove abnormal complement pathway components and replace them with normal components may support its use in some patients with TMAs other than TTP and TMA-complement mediated.

Atypical Hemolytic Uremic Syndrome: A Brief Review

Atypical hemolytic uremic syndrome (aHUS) is a disease characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia and acute kidney injury. The histopathologic lesions of aHUS include thrombotic microangiopathy involving the glomerular capillaries and thrombosis involving arterioles or interlobar arteries. Extra-renal manifestations occur in up to 20% of patients. The majority of aHUS is caused by complement system defects impairing ordinary regulatory mechanisms. Activating events therefore lead to unbridled, ongoing complement activity producing widespread endothelial injury. Pathologic mutations include those resulting in loss-of-function in a complement regulatory gene (CFH, CFI, CD46 or THBD) or gain-of-function in an effector gene (CFB or C3). Treatment with the late complement inhibitor, eculizumab – a monoclonal antibody directed against C5 – is effective.

Pernicious Anemia Associated Cobalamin Deficiency and Thrombotic Microangiopathy: Case Report and Review of the Literature

A 43-year-old Hispanic male without significant previous medical history was brought to emergency department for syncope following a blood draw to investigate a 40 lbs weight loss during the past 6 months associated with decreased appetite and progressive fatigue. The patient also reported a 1-month history of jaundice. On examination, he was hemodynamically stable and afebrile with pallor and diffuse jaundice but without skin rash or palpable purpura. Normal sensations and power in all extremities were evident on neurological exam. Presence of hemolytic anemia, schistocytosis, thrombocytopenia, and elevated lactate dehydrogenase (LDH) was suggestive of thrombotic thrombocytopenic purpura (TTP). However, presence of leukopenia, macrocytes, and an inadequate reticulocyte response to the degree of anemia served as initial clues to an alternative diagnosis. Two and one units of packed red blood cells were transfused on day 1 and day 3, respectively. In addition, one unit of platelets was transfused on day 2. Daily therapeutic plasma exchange (TPE) was initiated and continued until ADAMTS-13 result ruled out TTP. A low cobalamin (vitamin B12) level was evident at initial laboratory work-up and subsequent testing revealed positive intrinsic factor-blocking antibodies supporting a diagnosis of pernicious anemia with severe cobalamin deficiency. Hematological improvement was observed following vitamin B12 supplementation. The patient was discharged and markedly improved on day 9 with outpatient follow-up for cobalamin supplementation.

Current evidence on the discontinuation of eculizumab in patients with atypical haemolytic uraemic syndrome

Background. Atypical haemolytic uraemic syndrome (aHUS) is a rare, life-threatening disorder for which eculizumab is the only approved treatment. Life-long treatment is indicated; however, eculizumab discontinuation has been reported. Methods. Unpublished authors' cases and published cases of eculizumab discontinuation are reviewed. We also report eculizumab discontinuation data from five clinical trials, plus long-term extensions and the global aHUS Registry. Results. Of six unpublished authors' cases, four patients had a subsequent thrombotic microangiopathy (TMA) manifestation within 12 months of discontinuation. Case reports of 52 patients discontinuing eculizumab were identified; 16 (31%) had a subsequent TMA manifestation. In eculizumab clinical trials, 61/130 patients discontinued treatment between 2008 and 2015. Median follow-up post-discontinuation was 24 weeks and during this time 12 patients experienced 15 severe TMA complications and 9 of the 12 patients restarted eculizumab. TMA complications occurred irrespective of identified genetic mutation, high risk polymorphism or auto-antibody. In the global aHUS Registry, 76/296 patients (26%) discontinued, 12 (16%) of whom restarted. Conclusions. The currently available evidence suggests TMA manifestations following discontinuation are unpredictable in both severity and timing. For evidence-based decision making, better risk stratification and valid monitoring strategies are required. Until these exist, the risk versus benefit of eculizumab discontinuation, either in specific clinical situations or at selected time points, should include consideration of the risk of further TMA manifestations.

Atypical Hemolytic Uremic Syndrome Secondary to Lupus Nephritis, Responsive to Eculizumab

Among the spectrum of disease manifestations associated with systemic lupus erythematosus, lupus nephritis is particularly concerning due to the potential for renal failure. This autoimmune attack may not, however, be limited to the kidney and is increasingly being recognized as a trigger for atypical Hemolytic Uremic Syndrome (aHUS). Atypical HUS falls under the spectrum of the thrombotic microangiopathies (TMAs) – a group of disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia, and end organ damage. Although plasma exchange is considered first-line therapy for thrombotic thrombocytopenic purpura – a TMA classically associated with autoimmune depletion of ADAMTS-13 – aHUS demonstrates less reliable responsiveness to this modality. Instead, use of the late complement inhibitor Eculizumab has emerged as an effective modality for the management of such patients. Diagnosis of aHUS, however, is largely clinically based, relying heavily upon a multidisciplinary approach. Herein we present the case of a patient with atypical HUS successfully treated with Eculizumab in the setting of Class IV-G (A) lupus nephritis and hypocomplementemia.

Management of Thrombotic Microangiopathic Hemolytic Anemias with Therapeutic Plasma Exchange: When It Works and When It Does Not

Thrombotic microangiopathies are a heterogeneous group of inherited and acquired disorders sharing a common clinical presentation of microangiopathic hemolytic anemia, thrombocytopenia, and organ damage. These disorders have been treated with plasma exchange (TPE) based on randomized controlled trials, which found this therapy to be effective in thrombotic thrombocytopenic purpura (TTP). For the remaining disorders, low- to very low-quality evidence exists for the use of TPE. When TPE is applied, the treatment regimen used for TTP is usually applied. There is a need for further evaluation of the role of TPE in the treatment of thrombotic microangiopathies other than TTP.