Frontiers in pathophysiology and management of thrombotic thrombocytopenic purpura

HIV-Associated Thrombotic Thrombocytopenic Purpura in a Virally Suppressed Patient With Normal CD4 Count: A Rare Presentation

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic process characterized by multiorgan failure secondary to microvascular thrombi comprising platelets and von Willebrand factor. HIV is a known risk factor for TTP. However, patients generally have low CD4+ count during initial presentation or subsequent flare-ups. This case report describes a 69-year-old man with HIV who presented with an initial presentation of TTP while having a prior history of HIV with a normal CD4 count and undetectable viral load on presentation. A 69-year-old Caucasian male with a previous history of HIV on antiretroviral therapy (ART), a history of recurrent deep vein thrombosis maintained on Coumadin, and no previous history of tobacco dependence or substance use presented to the emergency department with symptoms of fatigue and dyspnea worsening on exertion. The patient had stable vital signs on arrival. The initial lab workup was remarkable for hemoglobin of 9.3 g/dL, hematocrit 29%, platelets 22 x 109/L, prothrombin time (PT) 51 seconds, activated partial thromboplastin time (PTT) 41 seconds, international normalized ratio (INR) 4.3 (on warfarin), blood urea nitrogen (BUN) 29 mg/dL, creatinine 2.0 mg/dL, total bilirubin 1.8 mg/dL, lactate dehydrogenase (LDH) 1229 U/L, haptoglobin less than 10 mg/dL, reticulocyte count 6.21%, fibrinogen 519 mg/dL, and D-dimer within normal limits. A clinical diagnosis of TTP was made with a peripheral blood smear showing schistocytes, as well as evidence of hemolytic anemia and thrombocytopenia. Prompt initiation of treatment with plasma exchange therapy was started. The patient was also given high-dose steroids and prednisone 1 mg/kg with a prolonged taper. Due to the delay in improvement in platelet count, the patient was also given concurrent rituximab therapy. TTP in HIV is rare, primarily seen in HIV patients who have a high viral load, low CD4 count, or if there is a delay in starting ART. In HIV-induced TTP patients, the relationship between CD4 count and viral load is complex and not fully elucidated. Further research is needed to understand better the interplay between HIV parameters (such as CD4 count and viral load) and the development of TTP in HIV-infected individuals who are already on treatment. This understanding could aid in identifying high-risk patients and developing targeted interventions to prevent or manage TTP in this population.

A comparative study of anti-ADAMTS-13 antibody dynamics in immune-mediated thrombotic thrombocytopenic purpura

Background

Thrombotic thrombocytopenic purpura, particularly its immune-mediated variant (iTTP), necessitates accurate diagnostic approaches for effective management.

Objectives

To compare a chemiluminescence immunoassay (CLIA) and an enzyme-linked immunosorbent assay (ELISA) for testing ADAMTS-13 activity and detecting anti-ADAMTS-13 autoantibodies (AAbs) in patients with iTTP.

Methods

This study involved 31 paired samples from 12 iTTP patients. ADAMTS-13 activity was measured using the HemosIL AcuStar (Instrumentation Laboratory, CLIA) and Technozym (Technoclone) activity assay (ELISA). The presence of AAbs was assessed using Technozym ADAMTS-13-INH assay (ELISA) and HemosIL AcuStar activity (CLIA) within a Bethesda assay following mixing with normal pool plasma. von Willebrand factor (VWF) multimers were analyzed using the HYDRASYS-2 SCAN system and the HYDRAGEL 5- or 11-VW Multimer kits (Sebia). VWF activity levels were measured with the HemosIL AcuStar VWF:GPIbR on the ACL AcuStar Analyzer (IL).

Results

For ADAMTS-13 activity, a strong linear relationship and no bias between CLIA and ELISA were confirmed (slope = 1.01 [0.91, 1.11], intercept = 0.00 [-0.47, 0]). However, significant discrepancies were found in AAb detection during remission phases with ADAMTS-13 activity between 10% and 50%, with CLIA and ELISA showing significant divergence (P < .001, Cohen's g = 0.34). Consistently, VWF multimers and activity levels exhibited significantly different values between remission samples with ADAMTS-13 activity below 50% and above 50%. In longitudinal analysis of patients with multiple iTTP relapses, positivity to CLIA appears to precede ELISA in predicting exacerbations.

Conclusion

While CLIA and ELISA might be interchangeable for assessing ADAMTS-13 activity, they are not equivalent for detecting AAbs, particularly in patients in clinical remission with ADAMTS-13 activity between 10% and 50%.

Efficacy and relative safety of caplacizumab in immune-mediated thrombotic thrombocytopenic purpura: a systematic review and meta-analysis

Immune-mediated thrombotic thrombocytopenia purpura (iTTP) is a rare microvascular disease characterized by severe disseminated microvascular thrombose-bleeding syndrome. Caplacizumab has been approved for the treatment of iTTP in combination with Plasma Exchange (PE) and immunosuppressive therapy, but its role in iTTP therapy remains uncertain. Therefore, we conducted a meta-analysis to investigate the safety and efficacy of caplacizumab for the treatment of patients with iTTP. We searched electronic databases (PubMed, Embase, Cochrane Library, and Scopus) and reference lists of relevant articles to find articles published from 2015 to 2022. The time to normalization of the platelet count of the group caplacizumab is shorter than the group placebo (SMD = -0.72; 95% CI -0.88 to -0.56; P  < 0.05). Caplacizumab reduced the incidence of mortality (OR = 0.41; 95% CI 0.18-0.92; P  < 0.05), exacerbations (OR = 0.10; 95% CI 0.05-0.18; P  < 0.05), and recurrence (OR = 0.17; 95% CI 0.06-0.50; P  < 0.05). However, the bleeding events in the caplacizumab group were higher than those in the placebo group, especially severe bleeding events. There was no difference in ADAMTS13 activity and thromboembolic events between the two groups. Our analysis indicated that caplacizumab is effective and well tolerated for the treatment of iTTP.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42022362370.

Apadamtase Alfa: First Approval

Apadamtase alfa (ADAMTS13, recombinant-krhn; ADZYNMA), a human recombinant form of a disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13), is being developed by Takeda under license from KM biologics for thrombotic thrombocytopenic purpura (TTP) and sickle cell disease. On 9 November 2023, apadamtase alfa was approved in the USA for prophylactic and on-demand enzyme replacement therapy (ERT) in paediatric and adult patients with congenital TTP. Apadamtase alfa is under regulatory review for congenital TTP in the EU and Japan, and is under clinical development for immune-mediated TTP in several countries worldwide. Clinical development of apadamtase alfa for vaso-occlusive crisis related to sickle cell anaemia is underway in the USA. This article summarizes the milestones in the development of apadamtase alfa leading to this first approval in the USA for congenital TTP.

Plasmapheresis in the ICU

Therapeutic plasma exchange (TPE) is a treatment paradigm used to remove harmful molecules from the body. In short, it is a technique that employs a process that functions partially outside the body and involves the replacement of the patient's plasma. It has been used in the ICU for a number of different disease states, for some as a first-line treatment modality and for others as a type of salvage therapy. This paper provides a brief review of the principles, current applications, and potential future directions of TPE in critical care settings.

Successful Treatment of Refractory Thrombotic Thrombocytopenic Purpura (TTP) With Caplacizumab: A Case Report

We report a female patient who presented with generalized weakness, episodes of altered mental status and slurred speech, and a history of systemic lupus erythematosus. Initial investigations showed profound thrombocytopenia and schistocytosis on peripheral blood smear. PLASMIC score was promptly calculated, and plasma exchange with steroids was initiated based on the initial high PLASMIC score. Bone marrow examination showed hypocellular marrow without any other obvious abnormalities. The patient's platelet counts initially improved but had a quick decline, on which, rituximab and subsequently caplacizumab were introduced. The patient was discharged after stabilization with plasma exchange (PLEX) therapy as needed on an outpatient basis.