Hemophilia is derived from hemo (blood) and philia (love), is recognized as the most common and severe hemorrhagic disorder. Depending upon the pathophysiology, there are three types of hemophilia -A, B, and C, caused by the deficiency or dysfunction of factors VIII, IX, and XI, respectively. It can be hereditary, which is more common, and a rare variety is the acquired one. Acquired hemophilia is due to the autoantibodies that develop against a coagulation factor. Mostly the antibodies develop against the factor VIII, hence commonly known as "acquired hemophilia A" (AHA).
Patients with autoantibodies may present with catastrophic bleeding; they usually do not have any past medical history of bleeding episodes or disorder. Its diagnosis is often difficult because of its rarity and the complexity of the laboratory workup. This article describes the clinical and biological features, in addition to the therapeutic strategies for this disease.
Clinically, the presentation varies from life-threatening bleeds on one end to the mild or no bleeds on the other end. The presentation with life-threatening bleeding is usually seen during the initial several weeks, although it can happen at any point during disease if the appropriate treatment is not initiated.
In about half of the cases diagnosed with acquired hemophilia, no cause or precipitating factor is recognized. For the other half, an underlying disease or a precipitating factor can be identified. Various factors that can predispose to the development of acquired hemophilia A (AHA) may include the following,
Acquired hemophilia is rare, with an overall incidence of 1.5 per million per year. However, the incidence varies with age from 0.045 per million per year in children younger than 16 years of age to 14.7 per million per year in adults older than 85 years. Hence, the disease is more common in adults than in children. There are reports that 80% of the patients are older than 65 years. The median age ranges from 73.9 years to 78 years. There has been no evidence of any genetic pattern and is overall equal in males and females.
Although in the age bracket 20 to 40 years it is more common in females while in adults older than 85 years, it is more commonly seen in males. The increased incidence in females in the reproductive years (20 to 40 years) can be attributed to the higher risk of the disease during pregnancy, in the post-partum period until 12 months after delivery.
Factor VIII (FVIII) serves as a cofactor to factor IX (FIX) for the conversion of factor X (FX) to Xa and hence leading to the production of thrombin on the activated platelets’ surface. Factor VIII is a 330-kDa precursor protein. The proteolytic processing converts the domain structure of factor VIII from A1-a1-A2-a2-B-a3-A3-C1-C2 into heterodimers of heavy and light chains. Most of the acquired inhibitors of FVIII bind to the A2, A3, or C2 domains. The domains A2 and A3 are responsible for factor VIII binding to factors IXa and X, while the domain C2 binds factor VIII to the phospholipids and von Willebrand factor. Autoantibodies that develop in patients with acquired hemophilia are non-complement fixing as well as non-precipitating, belong to the IgG class (mostly IgG1 and IgG4).
These antibodies bind to the domains in time and the temperature-dependent manner in second-order kinetics. However, they do not result in complete factor VIII inactivation invitro; the measurable factor activity offers little if no clinical benefit in controlling hemorrhage. The kinetics of antibody interaction with factor VIII vary with the autoantibodies in acquired hemophilia A (AHA) and alloantibodies that appear in congenital hemophilia. Alloantibodies can altogether abolish the factor activity, whereas the autoantibodies result in markedly decreased factor activity, although the slight residual FVIII activity is not protective clinically. The breakdown of immune tolerance can result from a combination of genetic and environmental factors. FVIII deficiency results in insufficient production of thrombin on the surface of activated platelets.
A complete history should be taken of immunological diseases, the medication, as well as the broad range of associated medical conditions that predispose the patient for acquired hemophilia. The age, gender, presenting complaints, past medical history, previous surgical notes, and drug history should be carefully assessed to make a differential diagnosis. The diagnosis of acquired hemophilia A (AHA) should be considered in patients with a recent onset of abnormal bleeding, especially in the elderly and peripartum women. The presentation of an elderly patient or one during the post-partum period with acute and new-onset bleeding with no prior history of any bleeding should raise suspicion for AHA in the mind of the provider. However, it should be kept in mind that almost 50% of the patients diagnosed with acquired hemophilia do not have any precipitating or predisposing factor.
Sometimes the clinical picture is mild. However, they should not be neglected because they are often the first manifestation of a condition that can be life-threatening at any time with the occurrence of severe bleeding events.
The rarity of this pathology can be the reason for an excessive delay in diagnosis. Whenever the history points out any etiological factor, a complete and detailed physical examination should be carried out in addition to ordering investigations to reach the diagnosis. The patients develop spontaneous, extensive subcutaneous hematomas, without favoring factor. The classical presentation is with purpura and soft tissue bleeding. More severe hemorrhagic complications are also possible, which are discussed later. Unlike congenital hemophilia, hemarthrosis is uncommon.
When the history and physical examination raise suspicion, the diagnosis of acquired hemophilia should be confirmed by a complete blood count and a coagulation profile. The complete blood test reveals a normal platelet count, whereas the coagulation profile shows an isolated prolonged activated partial thromboplastin time (aPTT) by 2 to 3 times its normal value. Prolonged aPTT can be attributed to the deficiency of multiple factors of the intrinsic pathway, including FVIII, FIX, FXI, FXII, as well as the presence of antibodies against these factors. To rule out either of the causes of the functional deficiency of the factors mixing studies are helpful.
These studies are performed by mixing normal plasma with that of the patient in a 1 to 1 ratio. An improvement in the aPTT after a mixing study points to the deficiency of coagulation factors in the patient, whereas if the mixing study does not correct the aPTT, it points to the presence of factor inhibitors, that have rendered the normal plasma factors dysfunctional as well. The mixing study requires the plasma to be incubated for 1 to 2 hours before proceeding with the study. The quantitative assays of factor activity and measurement of factor inhibitor levels should be performed and are considered diagnostic. In addition to an isolated prolonged aPTT, a failed mixing study, and normal prothrombin time (PT), a patient with acquired hemophilia also shows a decreased FVIII activity and increased levels of factor inhibitor autoantibodies.
The antibody titers are described in the Bethesda unit (BU), which represents the amount of inhibitor that leads to 50% residual FVIII:C activity. The Nijmegen modification to the Bethesda method has helped to standardize the acidity as well as the concentration of protein in the testing mixture, which reduces the probability of an artifactual measurement, hence leading to increased specificity of the test.
In cases with massive bleeding, the complete blood count may reveal decreased hemoglobin levels. There are rare cases where patients do not have a prolonged aPTT, hence in such incidents, the clinical judgment of the provider, as well as interprofessional team collaboration, is required.
The treatment recommendations usually rely on the clinical judgment and expertise of the providers who have treated patients with acquired hemophilia A (AHA). The reason being the unavailability of an international consensus for management.
The management of AHA, however, comprises of a two-pronged therapy approach in which both modalities go hand in hand. These are
The requirement for hemostasis management is primarily dependent on the severity of bleeding, as well as its location. It should be noted that the autoantibody titer is not directly correlated to the bleeding severity. As mentioned earlier, although there might be some residual factor activity detectable, it does not play a vital role in the clinical picture of the patient.
In a patient that presents with mild bleeding and is not needing to undergo an emergent invasive procedure, with autoantibody titers of equal to or less than five BU, observation is sufficient. These titers have been reported to disappear in 25% of cases within a few months when these were secondary to pregnancy or antimicrobial therapy. In cases with minor bleeding that require treatment, the approach is usually limited to avoiding any invasive procedure as well as the discontinuation of medication that is associated with bleeding. In patients with a residual factor VIII levels of more than 5 percent and autoantibody titers less than 2 BU, desmopressin (0.3–0.4 mg/kg) has been reported to be helpful with increasing the factor VIII levels. However, the rise in factor levels is transient but usually proves to be useful in minor bleeding cases. As compared to desmopressin, the human factor VIII is found to be superior in situations with low autoantibody titers, but the requirement of extraordinary amounts of FVIII, to saturate the neutralizing autoantibody, is a significant limitation.
Patients who present with major bleeding (72%) require initiation of appropriate antihemorrhagic treatment in a timely fashion. Suppose the antibody titer is low (<5BU) treatments, including human factor VIII or desmopressin, may be considered as the first-line therapy if the hemostatic levels of FVIII can be achieved which is only possible with low titers of antibody. In cases with high titers, first-line treatment is the use of bypassing agents. The bypassing agents are named so because of their mechanism of action. They act by bypassing the need for factor VIII in the coagulation pathway in the production of thrombin. These agents include activated prothrombin complex concentrate (aPCC) and recombinant activated Factor VII (rFVIIa). The prothrombin complex concentrate, which is plasma-derived and contains exogenously activated vitamin K dependent factors (factors II, VII, IX, X).
Although both bypassing agents differ in their pharmacokinetics and biochemical properties, neither has shown to be more effective over the other in the clinical settings. Some studies do suggest that rFVIIa should be preferred over aPCC. However, the cost aspect of rFVIIa is a downside to its widespread usage. The recommended dosage of aPCC is 100 U/kg per dose or 200 u/kg/day. In contrast, the dosage of rFVIIa is similar to the one used in congenital hemophilia, i.e., 90 μg/kg every 2–3 hours until sufficient hemostasis has been achieved. The half-life of rFVIIa is about 2 hours, while that of aPCC is around 4 to 7 hours. Either of the two bypassing agents can be used as a first-line in the treatment. However, the choice can be influenced by the patient's history of response, patient's convenience, preference (recombinant vs. plasma derive product), and availability of the product. If the first-line therapy fails, evidence suggests prompt initiation of the alternate bypassing agent, may be useful. Using both agents simultaneously should be avoided except in cases of a failure of adequate response with one in a life-threatening bleeding scenario.
Treatment response is monitored clinically as no laboratory test has been approved for assessing the efficacy of the treatment. Global hemostatic assays have been used to determine thrombin generation, but, the results show no correlation with the patients' status clinically. Older patients and patients with comorbidities (cardiovascular diseases, cancers, and pregnancy) are a higher risk of developing complications, including arterial and venous thromboses, with the use of increased doses of these agents.
In the case of mucosal bleeding, there is supporting evidence for the concomitant use of antifibrinolytic therapy.
Once treatment is successful, to prevent bleeding in the future, there are recommendations for prophylactic therapy by using low doses of bypassing agents.
The treatment of AHA depends on correcting the pathophysiology that arises due to the presence of factor autoantibody. In the presence of the autoantibody, the patient is always at risk of life-threatening bleeding, and the complete eradication of the inhibitor is vital for improving survival in patients. Inhibitor eradication therapy should be initiated along with hemostatic therapy as the delay has been associated with poor patient outcomes. For this purpose, the first-line treatment includes prednisone (1 mg/kg/day). It can be used alone or cyclophosphamide (50 to 100 mg/day) can be added, although evidence suggests that the combined use is correlated with better patient outcomes.
The inhibitor eradication therapy is considered successful with undetectable titers of autoantibody (<0.6 BU) along with normal factor VIII levels (>50%). Indications for second-line immunosuppression include factor VIII levels not increasing, and autoantibody titers are not decreasing at 3 to 5 weeks with appropriate treatment and adequate patient compliance. Relapse may occur, which imposes a long follow up. Rituximab is an anti-CD20 monoclonal antibody successfully applied in the management of various autoimmune conditions and may be a valuable agent in managing acquired hemophilia. It may be considered in cases of intolerance to standard immunosuppressive therapy or resistance. 2-chlorodeoxyadenosine has also been shown to be effective in the treatment of some trials.
The hemorrhage due to acquired hemophilia is challenging to differentiate from other bleeding diatheses. The main differential diagnosis includes
Three extensive studies have shown that the mortality rate of acquired hemophilia A (AHA) lies between 8% to 22%. Still, more recent studies have shown lower mortality rates owing to the anti-hemorrhagic treatments.
Low FVIII is associated with a lower rate of complete remission and survival. Besides incomplete remission, other risk factors for death include advanced age and underlying malignancy. The development of alloantibodies in congenital hemophilia has shown no correlation with mortality as opposed to the autoantibodies in acquired hemophilia.
However, in the post-partum period, AHA has an excellent prognosis in about 97% of the patients. In many cases of AHA that occur in the post-partum period, spontaneous remission has been reported with the disappearance of the autoantibodies at an average of 30 months.
Acquired hemophilia can lead to several complications if the appropriate treatment is not initiated in a timely fashion. A few common complications include
The patients should be educated about compliance with medication as well as the complications that can arise. The patients should be told regarding the importance of close follow up with the provider for monitoring and the relapse of acquired hemophilia. Due to the risk of relapse, patients should promptly consult a provider in case of bleeding so that disease recurrence can be detected as early as possible. Patients should be provided with written instructions about the procedures that predispose the patient to a risk of bleeding like shaving, brushing teeth, etc. to achieve better patient outcomes.
Diagnosis should be suspected in case of bleeding in a patient without a history of coagulopathy.
The diagnosis must be considered in the presence of an isolated prolonged aPTT.
As acquired hemophilia is a rare but potentially life-threatening disease, it is a clinically challenging condition. Because this disease can be challenging to manage, patients should be referred to a specialized center for hemophilia, and any invasive procedures that need to be performed diagnostically or therapeutically should require clearance from the specialists.
Acquired hemophilia lacks specific treatment recommendations due to the absence of high-level evidence as opposed to the congenital form. The guidelines developed for congenital hemophilia may be utilized to support decisions in acquired hemophiliacs.
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