Introduction: When Vascular Fragility Meets Vascular Remodeling
Pulmonary arterial hypertension (PAH) is a relentlessly progressive disease characterized by pulmonary vascular remodeling, elevated pulmonary vascular resistance, and right ventricular failure. Despite advances in targeted therapies, outcomes remain suboptimal in a subset of patients, particularly those with complex genetic or structural comorbidities.
Hereditary hemorrhagic telangiectasia (HHT) represents a distinct and paradoxical vascular disorder. Defined by fragile, malformed blood vessels and recurrent hemorrhage, HHT appears, at first glance, fundamentally incompatible with therapies that influence angiogenesis, vascular signaling, or hematopoiesis. When PAH and HHT coexist, clinicians are confronted with a rare but formidable therapeutic dilemma.
The advent of sotatercept—a first-in-class activin receptor type IIA ligand trap—has disrupted conventional thinking in PAH management. By targeting dysregulated signaling within the transforming growth factor-β (TGF-β) superfamily, sotatercept addresses the structural biology of pulmonary vascular disease rather than merely its hemodynamic consequences. Its use in HHT-associated PAH, however, raises immediate and legitimate concerns regarding bleeding risk.
This article examines the rationale, implications, and broader clinical significance of sotatercept therapy in PAH complicated by HHT, using a landmark case as a foundation for a deeper, practice-oriented discussion.
Pulmonary Arterial Hypertension in the Context of HHT
Pulmonary hypertension in patients with HHT is heterogeneous. Most cases arise from high-output states secondary to hepatic arteriovenous malformations, leading to elevated pulmonary pressures with relatively preserved pulmonary vascular resistance. Management in such cases focuses on controlling shunt physiology rather than pulmonary vasculopathy.
True pulmonary arterial hypertension, however, represents a far rarer phenotype in HHT. It mimics idiopathic or heritable PAH, with markedly elevated pulmonary vascular resistance, progressive right ventricular dysfunction, and poor long-term prognosis. This form is most commonly associated with pathogenic variants in genes encoding components of the TGF-β signaling pathway, particularly endoglin (ENG) and activin receptor-like kinase 1 (ALK1).
The coexistence of PAH and HHT is therefore not accidental but genetically coherent. Both diseases reflect dysregulation of vascular development, endothelial signaling, and cellular proliferation. This shared biology creates an opportunity—and a risk—for targeted intervention.
Therapeutic Constraints in HHT-Associated PAH
Standard PAH therapies target three principal pathways: endothelin signaling, nitric oxide signaling, and prostacyclin signaling. While effective in many patients, these agents present unique challenges in HHT.
Endothelin receptor antagonists may exacerbate anemia. Phosphodiesterase type 5 inhibitors have been associated with increased epistaxis and gastrointestinal bleeding. Prostacyclin pathway agents possess antiplatelet effects that may aggravate hemorrhagic tendencies. In patients with HHT, these risks are not theoretical; they frequently manifest clinically.
As a result, therapeutic escalation is often limited by bleeding rather than hemodynamics. Patients may reach maximal tolerated therapy while remaining symptomatic, functionally impaired, and at risk of disease progression. In this context, lung transplantation becomes the final option—a solution burdened by its own risks and limitations.
Sotatercept: A Mechanism Distinct from Vasodilation
Sotatercept introduces a fundamentally different approach to PAH therapy. Acting as a ligand trap for select members of the TGF-β superfamily, it restores balance between proliferative and antiproliferative signaling within the pulmonary vasculature. The result is inhibition of abnormal smooth muscle proliferation and promotion of vascular homeostasis.
Clinical trials have demonstrated substantial improvements in pulmonary vascular resistance, exercise capacity, and functional class when sotatercept is added to background PAH therapy. These effects suggest disease modification rather than transient symptomatic relief.
However, the same signaling pathways targeted by sotatercept are involved in angiogenesis and erythropoiesis. Reported adverse effects include epistaxis, telangiectasia formation, thrombocytopenia, and increases in hemoglobin levels. In HHT, where bleeding is intrinsic to the disease, these effects demand careful scrutiny.
Clinical Insight from a Landmark Case
The reported case involves a middle-aged woman with genetically confirmed HHT type 1 due to an ENG mutation, complicated by congenital heart disease and severe, long-standing PAH. Despite decades of treatment with prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase inhibitors, her disease progressed to the point of lung transplant evaluation.
The introduction of sotatercept marked a decisive shift. Within months, the patient experienced significant improvement in exertional capacity and quality of life—outcomes that had eluded years of maximal conventional therapy. This improvement was clinically meaningful, altering her functional trajectory and daily life.
Predictably, bleeding emerged as the principal adverse effect. The patient reported a marked increase in epistaxis frequency, from sporadic episodes to multiple events per week. Yet this increase did not translate into clinical deterioration. Hemoglobin levels rose rather than fell, reflecting sotatercept’s erythropoietic effects. No new telangiectasias, thrombocytopenia, or major hemorrhagic events were observed.
Understanding the Bleeding–Erythropoiesis Paradox
At first glance, increased bleeding accompanied by rising hemoglobin appears contradictory. However, this paradox is biologically plausible. Sotatercept inhibits activin signaling, a pathway known to suppress erythropoiesis. By lifting this suppression, the drug promotes red blood cell production, potentially offsetting blood loss from mucosal bleeding.
In the reported case, this balance favored hematologic stability despite increased epistaxis. While bleeding was subjectively bothersome, it remained manageable and did not compromise oxygen delivery or functional capacity. Importantly, the patient herself judged the trade-off acceptable, describing the benefits as “well worth it.”
This observation underscores a critical principle: bleeding risk must be evaluated not only by frequency, but by severity, reversibility, and overall impact on patient well-being.
Risk–Benefit Assessment in Advanced PAH
In patients with advanced, treatment-resistant PAH, the therapeutic goal shifts from optimization to salvage. At this stage, the alternatives to novel therapy are limited: progressive right heart failure, hospitalization, and transplantation.
Against this backdrop, the acceptance of moderate bleeding risk becomes rational rather than reckless. The key lies in careful patient selection, informed consent, and vigilant monitoring. Sotatercept should not be viewed as benign, but neither should it be dismissed solely on theoretical grounds.
This case illustrates that in selected patients, the benefits of sotatercept may decisively outweigh its risks—even in the presence of a bleeding-prone condition such as HHT.
Monitoring and Practical Management
The use of sotatercept in HHT-associated PAH demands a structured monitoring strategy. Baseline assessment should include bleeding history, hemoglobin levels, platelet counts, iron status, and epistaxis severity scoring. Early follow-up is essential, as bleeding events often occur within the first weeks of therapy.
Supportive management of epistaxis should be proactive rather than reactive. Nasal humidification, topical therapies, antifibrinolytics, and timely otolaryngology referral can substantially reduce symptom burden. Coordination with specialized HHT centers enhances safety and patient confidence.
Equally important is continuous reassessment of therapeutic goals. If bleeding becomes severe, refractory, or clinically destabilizing, dose adjustment or discontinuation must be considered. Flexibility and patient-centered decision-making are paramount.
Broader Implications for PAH Therapeutics
Beyond HHT, this case exemplifies a broader evolution in PAH management. Sotatercept represents a new class of agents that target vascular remodeling rather than vascular tone. As such therapies enter clinical practice, traditional contraindications and risk thresholds may require recalibration.
Rare disease populations often serve as stress tests for therapeutic innovation. Success in these settings does not guarantee universal applicability, but it expands the conceptual boundaries of what is possible. This first documented use of sotatercept in HHT-associated PAH does precisely that.
Conclusion: Innovation at the Edge of Evidence
The successful use of sotatercept in a patient with HHT-associated pulmonary arterial hypertension highlights both the promise and the complexity of next-generation PAH therapy. By addressing the structural drivers of disease, sotatercept offers hope where conventional therapies have failed.
The accompanying increase in bleeding underscores the need for caution, expertise, and individualized care. Yet it does not negate the drug’s potential value. In selected patients with advanced disease, sotatercept may offer meaningful improvement at an acceptable cost.
As evidence evolves, so too must clinical courage—tempered by vigilance, guided by biology, and anchored in patient priorities.
FAQ
Is sotatercept safe for patients with HHT and PAH?
Safety data are limited. Sotatercept may increase bleeding, but in selected patients with careful monitoring, benefits may outweigh risks.
Does increased epistaxis necessitate discontinuation of therapy?
Not necessarily. Severity, impact on hemoglobin, and patient tolerance should guide decisions rather than frequency alone.
Should sotatercept be considered before lung transplantation?
In treatment-resistant PAH, sotatercept may be considered as a bridge or alternative to transplantation on a case-by-case basis.
