TTP/HUS: observational studies generate hypotheses that lead to randomized controlled trials

Atypical haemolytic uremic syndrome (aHUS) and membranoproliferative glomerulonephritis (MPGN), different diseases or a spectrum of complement-mediated glomerular diseases?

Historically, patients with kidney diseases caused by genetic or acquired dysregulation of the complement alternative pathway have been grouped into clinical syndromes, C3 glomerulopathy (C3GN/DDD) and thrombotic microangiopathy (TMA), specifically atypical haemolytic uremic syndrome (aHUS). Recent data suggested that these diseases share a common pathophysiology and that patients can transition between glomerulopathies in this spectrum. Histopathologically, the main difference cited is the immunofluorescence (IF) findings, with C3 predominance in C3 glomerulopathy (compared with immunoglobulins and complements in immune complex-mediated membranoproliferative glomerulonephritis (MPGN)) and negative IF in TMA. We report a case in which a patient presented with hypertension, seizures, proteinuria, renal impairment and immune complex-mediated MPGN on kidney biopsy. Months later, she presented with classical TMA. She failed to respond to steroids and plasma exchange therapy but subsequently made a remarkable haematological and renal recovery after eculizumab treatment, thus supporting an underlying complement dysregulation and a diagnosis of aHUS.

Plasma exchange for kidney disease: what is the best evidence?

Therapeutic plasma exchange (TPE) has been used as adjunctive therapy for various kidney diseases dating back to the 1970s. In many cases, support for TPE was on mechanistic grounds given the potential to remove unwanted large molecular-weight substances such as autoantibodies, immune complexes, myeloma light chains, and cryoglobulins. More recently, growing evidence from randomized controlled trials, meta-analyses, and prospective studies has provided insights into more rational use of this therapy. This report describes the role of TPE for the 6 most common kidney indications in the 2013 Canadian Apheresis Group (CAG) registry and the evidence that underpins current recommendations and practice. These kidney indications include thrombotic microangiopathy, antiglomerular basement membrane disease, anti-neutrophil cytoplasmic antibody-associated vasculitis, cryoglobulinemia, recurrence of focal and segmental glomerulosclerosis in the kidney allograft, and kidney transplantation.

Development and validation of a predictive model for death in acquired severe ADAMTS13 deficiency-associated idiopathic thrombotic thrombocytopenic purpura: the French TMA Reference Center experience

BACKGROUND

Acquired thrombotic thrombocytopenic purpura is still associated with a 10-20% death rate. It has still not been possible to clearly identify early prognostic factors of death. This study involved thrombotic thrombocytopenic purpura patients with acquired severe (<10% of normal activity) ADAMTS13 deficiency and aimed to identify prognostic factors associated with 30-day death.

DESIGN AND METHODS

The study involved a prospective cohort of patients and was carried out between October 2000 and August 2010. A validation cohort of patients was set up from September 2010 to August 2011. Altogether, 281 (analysis cohort) and 66 (validation cohort) consecutive adult thrombotic thrombocytopenic purpura patients with acquired severe ADAMTS13 deficiency were enrolled. The study evaluated 30-day mortality after treatment initiation according to characteristics at inclusion.

RESULTS

Non-survivors (11%) were older (P=10(-6)) and more frequently presented arterial hypertension (P=5.10(-4)) and ischemic heart disease (P=0.013). Prognosis was increasingly poor with age (P=0.004). On presentation, cerebral manifestations were more frequent in non-survivors (P=0.018) and serum creatinine level was higher (P=0.008). The most significant independent variables determining death were age, severe cerebral involvement and LDH level 10 N or over. A 3-level risk score for early death was defined and confirmed in the validation cohort using these variables, with higher values corresponding to increased risk of early death.

CONCLUSIONS

A risk score for early death was defined in patients with thrombotic thrombocytopenic purpura and validated on an independent cohort. This score should help to stratify early treatment and identify patients with a worse prognosis.

Thrombotic microangiopathy: current knowledge and outcomes with plasma exchange

The classification of thrombotic microangiopathy has evolved and expanded due to treatment and mechanistic advances. The two basic clinical forms of thrombotic microangiopathy (excluding disseminated intravascular coagulation [DIC]), thrombotic thrombocytopenic purpura (TTP), and hemolytic uremic syndrome (HUS) encompass a wide range of primary and secondary forms. The advent of plasma therapy and the identification of an inhibitor to ADAMTS13 in the idiopathic or acute forms of TTP and its absence in diarrheal HUS have had a major impact on our current classification of thrombotic microangiopathy. In adults, the difficulty of differentiating TTP, which is much more common than HUS and the need for a speedy diagnosis to provide life-saving plasma therapy has resulted in the term TTP/HUS for adult forms of thrombotic microangiopathy that present with unexplained thrombocytopenia and microangiopathic hemolytic anemia without a DIC. In this adult population a primary idiopathic and hereditary form as well as eight known secondary categories or clinical forms of TTP/HUS have been identified. HUS also embraces a primary (atypical HUS) and secondary forms (majority, diarrheal HUS secondary to Escherichia coli 0157:H7). In children, who present with HUS with no preceding history of diarrhea, plasma therapy is also offered on an urgent basis and studies are carried out to determine if they are suffering an abnormality in complement activation that may require eculizumab therapy. The advent of plasma therapy in the treatment of thrombotic microangiopathy has led to a clearer understanding of the role of ADAMTS13, both short- and long-term outcomes and the need for future surveillance and intervention.

Attending rounds: microangiopathic hemolytic anemia with renal insufficiency

The classification of thrombotic microangiopathy has evolved and expanded due to treatment and advances in understanding of the diseases associated with this clinical presentation. The three clinical forms of thrombotic microangiopathy-thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS), and disseminated intravascular coagulation-encompass a wide range of disorders that can be classified as either primary (idiopathic) or secondary to another identifiable disease or clinical context. Identification of an inhibitor to a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) in the idiopathic and acute forms of TTP, recognition of the absence of ADAMTS13 inhibition in diarrheal HUS, identification of complement abnormalities in atypical HUS, and a better understanding of the role of plasma therapy, rituximab, and eculizumab therapy have all had a major effect on current understanding of the thrombotic microangiopathies. In this Attending Rounds, a patient with a thrombotic microangiopathy is presented, along with discussion highlighting the difficulty of differentiating TTP from HUS and disseminated intravascular coagulation, the need for a prompt diagnosis, and the role for plasma therapy in appropriately selected patients. The discussion attempts to provide a simple clinical approach to the diagnosis, treatment options, and future course of adults and children suffering from a thrombotic microangiopathy.