Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, clonal disorder of hematopoietic stem cells manifesting as hemolytic anemia, marrow failure, smooth muscle dystonia, and thrombosis. Deficiency of the glycosylphosphatidylinositol-anchored complement regulatory proteins, CD55 and CD59, due to somatic mutation of the phosphatidylinositol glycan class A (PIGA) gene, leads to complement-mediated lysis of PNH erythrocytes and activation of platelets, monocytes, and granulocytes.¹ Eculizumab and the newer, four-times longer half-life drug, ravulizumab, are humanized monoclonal antibodies that interfere with the cleavage of complement C5 and have changed the natural history of PNH.

Prior to therapeutic complement inhibition, thromboembolism (TE) was the leading cause of death in PNH.² Complement inhibitors are highly effective in reducing TE. In the combined clinical trials of eculizumab, Hillmen et al. found that eculizumab led to an 85% relative reduction in TE, but many patients remained on concomitant anticoagulation for both primary and secondary prophylaxis.³ In another study by Kelly et al., 58% of patients were on anticoagulation at the initiation of eculizumab and 45% of patients stopped primary prophylaxis with anticoagulation, but only one patient stopped anticoagulation for secondary prophylaxis.⁴ No thrombotic events were observed. Correlative laboratory data also supports that eculizumab decreases plasma markers of thrombosis, such as levels of prothrombin fragment F1 + 2, d-dimer and plasmin–antiplasmin complexes, and endothelial cell activation, such as tissue plasminogen activator, von Willebrand factor, and tissue factor pathway inhibitor.⁵ Primary prophylactic anticoagulation has not proven to be beneficial with the use of complement inhibitors, however, there is no data on how to manage anticoagulation in the setting of secondary prophylaxis.² Whether indefinite anticoagulation adds to secondary prevention of thrombosis in patients well controlled on terminal complement inhibition without additional risk factors remains an unanswered management dilemma in PNH, an important question since the median age of PNH is less than 50 years old and many have baseline thrombocytopenia.^{1, 6}

We identified 22 PNH patients evaluated at Johns Hopkins Hospital over a 15-year period from 2005 to 2020 with a history of TE, who were treated with C5 inhibition. Patients who met the following criteria were included: documented PNH clone in two cell lineages as assessed by flow cytometry, treatment with C5 inhibition for >6 months, history of TE, and 18 years or older at data collection. TE was confirmed by imaging or based on high clinical suspicion at the discretion of the treating hematologist. Eculizumab and ravulizumab were dosed at standard maintenance doses of 900 mg every 14 ± 2 days and 3300 mg every 8 weeks, respectively, except in five patients who received higher doses of eculizumab due to breakthrough hemolysis. Anticoagulation included warfarin, direct-acting oral anticoagulants, and low molecular weight heparin at therapeutic doses at the discretion of the treating physician. The study was approved by the Institutional Review Board of Johns Hopkins Hospital.

We evaluated thrombosis rates for the periods pre-C5 inhibition and following initiation of anti-C5 therapy in patients on complement inhibition alone and in those who remained on concomitant anticoagulation. The pretreatment patient-years (pre-C5 inhibition) included all TE events between diagnosis of PNH and treatment with a terminal complement inhibitor. The period on C5 inhibition was defined as the time from treatment initiation with C5 inhibition through the last follow-up or bone marrow transplant. We considered patients as being treated with C5 inhibitor monotherapy if they were never treated with anticoagulation or discontinued anticoagulation and remained on a C5 inhibitor alone. In the “C5 inhibitor monotherapy” group, we counted only the years since initiation of C5 inhibition and discontinuation of anticoagulation.

The incidence of TE was calculated as TE events per patient-years. We compared paired observations for thrombosis rates pre-treatment and while on C5 inhibition (with or without concomitant anticoagulation) using the exact Poisson method. Two-sided exact mid-p values are provided and p < .05 is considered significant.

Eighteen patients were treated with C5 inhibition alone without therapeutic anticoagulation, including 12 patients who discontinued anticoagulation after initiation of the C5 inhibitor and 6 patients who never received anticoagulation or could not tolerate anticoagulation. Four patients were treated with a C5 inhibitor and maintained on indefinite anticoagulation. The patients who continued on indefinite anticoagulation either had additional hypercoagulable risk factors (n = 2; one patient with antiphospholipid syndrome and one with a strong family history of venous TE) or continued due to patient or physician preference (n = 2).

Patient and TE characteristics are presented in Table 1. The median number of years from PNH diagnosis to initiation of anti-C5 treatment was 4 (range, 0–14) years in the C5 inhibitor monotherapy patients and 3.5 (range, 0.5–8) years in the patients maintained on indefinite anticoagulation. The median time on treatment with C5 inhibition was similar between the groups (10 vs. 9.5 years). The median time on anticoagulation in the group on C5 inhibitor monotherapy was 4 (range, 0–132) months, whereas patients maintained on indefinite anticoagulation were treated with anticoagulation for a median of 9 (range, 4–19) years. Patients in whom anticoagulation was stopped once on complement inhibition overlapped anticoagulation and the C5 inhibitor for a median of 6 (range, 0–132) months. Ten of the 12 patients in whom anticoagulation was discontinued were treated with anticoagulation for at least 3 months consistent with treatment for acute venous TE. The decision to stop anticoagulation was at the discretion of the treating clinician reflective of patient preference and bleeding risk.

Patients on C5 inhibitor monotherapy had 25.91 events/100 patient-years prior to C5 inhibition (25 events) versus 1.45 events/100 patient-years post-C5 inhibition and off anticoagulation (two events) (p < .001) (Table S1). In the four patients who were treated with a C5 inhibitor and indefinite anticoagulation, there were 38.71 events/100 patient-years prior to the C5 inhibitor (6 events) and 5.41 events/100 patient-years after (2 events) (p = .01). This corresponds to a relative reduction of 94.4% in patients on C5 inhibitor monotherapy and 86.0% in patients on concomitant anticoagulation and C5 inhibition. TE events that occurred prior to C5 inhibitor therapy included intra-abdominal and cerebrovascular locations, whereas following treatment with a C5 inhibitor, thrombosis occurred in more common locations, such as deep vein thrombosis (DVT) and pulmonary embolism. Three of the four TE events occurring in patients on C5 inhibitors were provoked (two associated with major surgeries and bilateral DVTs attributed to uterine compression), whereas only one pretreatment event was considered provoked, associated with a venous access device. Two gastrointestinal bleeding events, one meeting International Society on Thrombosis and Haemostasis (ISTH) criteria for major bleeding, occurred among two patients on anticoagulation alone.

Our data suggest that discontinuation of anticoagulation for secondary prevention of TE in PNH patients well-controlled (lactate dehydrogenase < 1.5 times the upper limit of normal) on terminal complement inhibition may be safe. Further, discontinuation of anticoagulation may be advantageous in reducing bleeding risk and complications of thrombocytopenia resulting from comorbid bone marrow failure or liver disease.² Our rate of TE in patients on C5 inhibition and no anticoagulation (1.45 events/100 patient-years) was similar to that reported in patients on eculizumab ± anticoagulation (1.07 events/100 patient-years³ and 0.8 events/100 patient-years⁴). Our study looks specifically at patients with a history of TE as opposed to all PNH patients, which may select for patients with higher granulocyte clones and a thrombotic form of PNH.¹ Our median period on C5 inhibition and off anticoagulation was also longer than previously reported.

To our knowledge, this is the largest reported series of PNH patients with a history of thrombosis who discontinued anticoagulation. No randomized clinical trials exist to address whether anticoagulation can be discontinued in PNH patients on terminal complement inhibition. This question ideally would be answered using this modality, however, given the rarity of PNH, it is unlikely that such a trial will be performed. Further, registry data in PNH may lack the longitudinal follow-up to address this question. The limitations of this study include its single-center, retrospective design. In addition, anticoagulation compliance was not routinely collected. We describe a relatively small number of patients, owing to the rarity of this disease; however, we report a long duration of follow-up for the majority of patients.

Anticoagulation remains the mainstay of treatment for acute TE. C5 inhibition should be initiated expeditiously after a thrombotic event, as anticoagulation alone is ineffective in preventing recurrence of complement-mediated TE. This study supports the idea that untreated PNH is a provoking factor for TE, and select patients may not require indefinite anticoagulation if well-controlled on complement inhibition and there are no other persistent provoking risk factors for TE. We recommend overlapping anticoagulation and complement inhibition for 3–6 months following the acute thrombotic event unless contraindicated due to bleeding risk and/or thrombocytopenia. The potential additional benefit of continued anticoagulation in reducing thrombosis must be weighed against the risk of bleeding on an individual basis after an informed discussion with patients.

阵发性睡眠性血红蛋白尿 (PNH) 是一种罕见的造血干细胞克隆性疾病，表现为溶血性贫血、骨髓衰竭、平滑肌肌张力障碍和血栓形成。由于 A 类磷脂酰肌醇聚糖 ( PIGA ) 基因的体细胞突变，糖基磷脂酰肌醇锚定的补体调节蛋白 CD55 和 CD59 缺乏，导致补体介导的 PNH 红细胞裂解以及血小板、单核细胞和粒细胞的激活。¹ Eculizumab 和半衰期延长四倍的新型药物 ravulizumab 都是人源化单克隆抗体，可干扰补体 C5 的裂解，并改变了 PNH 的自然史。

在补体抑制治疗出现之前，血栓栓塞 (TE) 是 PNH 死亡的主要原因。²补体抑制剂对于降低 TE 非常有效。在依库珠单抗的联合临床试验中，Hillmen 等人。研究发现，依库丽珠单抗使 TE 相对减少 85%，但许多患者仍同时接受一级和二级预防的抗凝治疗。³在 Kelly 等人的另一项研究中，58% 的患者在开始使用依库珠单抗时接受抗凝治疗，45% 的患者停止抗凝一级预防，但只有一名患者停止抗凝治疗进行二级预防。⁴未观察到血栓事件。相关实验室数据还支持依库丽单抗降低血栓形成的血浆标志物，例如凝血酶原片段 F1 + 2、d-二聚体和纤溶酶-抗纤溶酶复合物的水平，以及内皮细胞活化，例如组织纤溶酶原激活剂、血管性血友病因子和组织因子途径抑制剂。⁵尚未证明一级预防性抗凝对于使用补体抑制剂有益，但是，没有关于如何在二级预防中管理抗凝的数据。²对于终末补体抑制得到良好控制而没有其他危险因素的患者，无限期抗凝是否能增加血栓形成的二级预防，这仍然是 PNH 中尚未解决的管理困境，这是一个重要的问题，因为 PNH 的中位年龄不到 50 岁，而且许多人有基线血小板减少症。^{1, 6}

我们确定了 22 名在 2005 年至 2020 年 15 年间在约翰·霍普金斯医院接受评估的有 TE 病史的 PNH 患者，这些患者接受了 C5 抑制治疗。符合以下标准的患者被纳入：通过流式细胞术评估，在两个细胞谱系中记录有 PNH 克隆，C5 抑制治疗>6 个月，有 TE 病史，并且数据收集时年龄为 18 岁或以上。TE 通过影像学或根据临床高度怀疑由治疗血液科医生自行决定确认。依库珠单抗和拉维珠单抗的标准维持剂量分别为每 14 ± 2 天 900 mg 和每 8 周 3300 mg，但 5 名患者因突破性溶血而接受更高剂量的依库珠单抗。抗凝治疗包括华法林、直接作用口服抗凝剂和低分子量肝素，治疗剂量由治疗医生酌情决定。该研究得到了约翰·霍普金斯医院机构审查委员会的批准。

我们评估了单独使用补体抑制的患者和仍同时接受抗凝治疗的患者在 C5 抑制前和开始抗 C5 治疗后的血栓形成率。治疗前患者年（C5 抑制前）包括 PNH 诊断和末端补体抑制剂治疗之间的所有 TE 事件。C5抑制期定义为从C5抑制治疗开始到最后一次随访或骨髓移植的时间。如果患者从未接受过抗凝治疗或停止抗凝治疗并继续单独使用 C5 抑制剂，我们认为患者正在接受 C5 抑制剂单药治疗。在“C5抑制剂单药治疗”组中，我们仅计算自开始C5抑制和停止抗凝治疗以来的年数。

TE 的发生率计算为每患者年的 TE 事件。我们使用精确泊松法比较了治疗前和 C5 抑制（联合或不联合抗凝治疗）期间血栓形成率的配对观察结果。提供了两侧精确的中间p值， p  < .05 被认为是显着的。

18 名患者仅接受 C5 抑制治疗，未进行抗凝治疗，其中 12 名患者在开始使用 C5 抑制剂后停止抗凝治疗，6 名患者从未接受过抗凝治疗或不能耐受抗凝治疗。4 名患者接受 C5 抑制剂治疗并维持无限期抗凝治疗。继续无限期抗凝治疗的患者要么有额外的高凝危险因素（n  = 2；一名患者患有抗磷脂综合征，另一名患者有强烈的静脉 TE 家族史），要么由于患者或医生的偏好而继续接受治疗（n  = 2）。

患者和 TE 特征如表 1 所示。从 PNH 诊断到开始抗 C5 治疗的中位年数在 C5 抑制剂单药治疗患者中为 4 年（范围为 0-14 年），而在 C5 抑制剂单药治疗患者中为 3.5 年（范围为 0.5-8 年）患者维持无限期抗凝治疗长达数年。两组间 C5 抑制治疗的中位时间相似（10 年与 9.5 年）。C5抑制剂单药治疗组的中位抗凝时间为4（范围，0-132）个月，而维持无限期抗凝治疗的患者的中位抗凝时间为9（范围，4-19）年。在补体抑制后停止抗凝治疗的患者中，抗凝治疗和 C5 抑制剂的重叠时间中位数为 6 个月（范围：0-132）。12 名停止抗凝治疗的患者中有 10 名接受了至少 3 个月的抗凝治疗，与急性静脉 TE 的治疗一致。停止抗凝治疗的决定由治疗临床医生根据患者偏好和出血风险酌情决定。

接受 C5 抑制剂单药治疗的患者在 C5 抑制前发生了 25.91 起事件/100 患者年（25 起事件），而在 C5 抑制后和停止抗凝治疗后发生了 1.45 起事件/100 患者年（2 起事件）（p < .001）（表S1  ） 。在接受 C5 抑制剂和无限期抗凝治疗的 4 名患者中，C5 抑制剂治疗前/100 患者年有 38.71 起事件/100 患者年（6 起事件）和 C5 抑制剂后/100 患者年有 5.41 起事件/100 患者年（2 起事件）（p =  . 01）。这相当于接受 C5 抑制剂单药治疗的患者相对减少了 94.4%，而同时接受抗凝和 C5 抑制的患者则相对减少了 86.0%。C5抑制剂治疗前发生的TE事件包括腹腔内和脑血管部位，而C5抑制剂治疗后，血栓形成发生在更常见的部位，例如深静脉血栓（DVT）和肺栓塞。服用 C5 抑制剂的患者发生的 4 例 TE 事件中有 3 例是诱发的（其中 2 例与大手术和子宫受压导致的双侧 DVT 相关），而只有 1 例治疗前事件被认为是诱发的，与静脉通路装置相关。两名仅接受抗凝治疗的患者发生了两起胃肠道出血事件，其中一件符合国际血栓与止血学会 (ISTH) 大出血标准。

我们的数据表明，对于末端补体抑制控制良好（乳酸脱氢酶 < 正常上限的 1.5 倍）的 PNH 患者，停止抗凝治疗以进行 TE 二级预防可能是安全的。此外，停止抗凝治疗可能有利于降低出血风险和由共病骨髓衰竭或肝病引起的血小板减少症的并发症。²接受 C5 抑制且未接受抗凝治疗的患者中的 TE 发生率（1.45 次事件/100 名患者年）与接受依库珠单抗 ± 抗凝治疗的患者报告的 TE 率相似（1.07 次事件/100 名患者年 3 和 0.8 次事件/100 名患者^年）⁴ ). 我们的研究专门针对有 TE 病史的患者，而不是所有 PNH 患者，这可能会选择具有较高粒细胞克隆和血栓形成 PNH 的患者。¹我们使用 C5 抑制和停止抗凝治疗的中位时间也比之前报道的要长。

据我们所知，这是有血栓形成史且停止抗凝治疗的 PNH 患者最大的报道系列。目前还没有随机临床试验来探讨是否可以在接受终末补体抑制的 PNH 患者中停止抗凝治疗。理想情况下，可以使用这种方式回答这个问题，但是，鉴于 PNH 的稀有性，不太可能进行这样的试验。此外，PNH 中的注册数据可能缺乏解决这个问题的纵向后续行动。这项研究的局限性包括其单中心、回顾性设计。此外，并未常规收集抗凝依从性。由于这种疾病的罕见性，我们描述的患者数量相对较少；然而，我们报告大多数患者的随访时间较长。

抗凝治疗仍然是急性 TE 的主要治疗方法。血栓事件后应立即开始 C5 抑制，因为单独抗凝治疗无法有效预防补体介导的 TE 复发。这项研究支持这样的观点，即未经治疗的 PNH 是 TE 的诱发因素，如果补体抑制得到良好控制，并且不存在其他持续诱发 TE 的危险因素，部分患者可能不需要无限期抗凝治疗。我们建议在急性血栓形成事件后 3-6 个月内同时进行抗凝和补体抑制，除非因出血风险和/或血小板减少而禁忌。在与患者进行知情讨论后，必须根据个体情况权衡持续抗凝治疗在减少血栓形成方面的潜在额外益处和出血风险。