Paroxysmal nocturnal haemoglobinuria (PNH) is a rare acquired haematopoietic stem cell disease characterized by complement-mediated intravascular hemolysis, thrombosis, and bone marrow failure. Eculizumab and ravulizumab are anti-C5 monoclonal antibodies that reduce hemolysis, anaemia and thrombotic risk, but are associated with increased risk of infection with encapsulated bacteria, including Neisseria meningitidis. We report a case of life-threatening infection by non-groupable Neisseria meningitidis in a young PNH patient treated with ravulizumab. Despite prompt admission to the intensive care unit, microbe isolation was delayed due to the negativity of capsular antigens, and the patient required intubation, dialysis, and transfusion support for pancytopenia. Notably, PNH disease activity remained controlled and no additional anti-C5 doses were administered. Increasing awareness regarding septic risk in PNH patients on complement inhibitors despite vaccinations is pivotal. A warning about serotypes generally not pathogenetic and not covered by vaccination, such as non-capsulated forms, is emerging.

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by intravascular hemolysis, thrombosis and bone marrow failure. Prior to the availability of specific therapy, PNH led to the death of around half of affected individuals, mainly through thrombotic complications, with a particular grim prognosis for patients presenting with classic PNH. The anti-C5 monoclonal antibody eculizumab has revolutionized treatment, controlling intravascular hemolysis and thrombosis occurrence, with improved long-term survival. However, eculizumab is infused on a lifelong 2 week basis and most of the patients are anemic, with some remaining transfusion-dependent. New anti-C5 agents reproduce the safety and efficacy of eculizumab, with improved patient convenience, while proximal complement inhibitors have been developed to address C3-mediated extravascular hemolysis, aiming to eventually improve hematological response. This review will describe the spectacular medical progress in PNH of the last 20 years, as well as the risks and benefits of a novel approach.

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized by complement-mediated intravascular haemolysis, severe thrombophilia and bone marrow failure. While for patients with bone marrow failure the treatment follows that of immune-mediated aplastic anaemia, that of classic, haemolytic PNH is based on anti-complement medication. The anti-C5 monoclonal antibody eculizumab has revolutionized treatment, resulting in control of intravascular haemolysis and thromboembolic risk, with improved long-term survival. Novel strategies of complement inhibition are emerging. New anti-C5 agents reproduce the safety and efficacy of eculizumab, with improved patient convenience. Proximal complement inhibitors have been developed to address C3-mediated extra-vascular haemolysis and seem to improve haematological response.