Background: Hemophilia B is a rare bleeding disorder in males, characterized by a deficiency in coagulation factor IX (FIX). Replacement of FIX with a recombinant FIX (rFIX) fusion protein, to sustain therapeutic plasma levels, is recommended as both treatment and prophylaxis to prevent bleeding episodes, particularly intracranial hemorrhage (ICH).
Case presentation: This case report outlines the management of ICH in a 7-month-old infant with severe hemophilia B, following an accidental trauma-related event, resulting in a thin compound fracture of the left occiput. FIX levels were extremely low (˂1.0%) and large deletions of the coagulation F9 gene (including exons 1-6) were identified. Intensive treatment with a rFIX fusion protein conjugated to the immunoglobulin Fc fragment (rFIXFc) continued for 18 days before hospital discharge. A continuous regimen of weekly rFIXFc infusions was implemented. Thirty days after initiating rFIXFc therapy, neutralizing antibodies or FIX inhibitors (common in patients with large F9 gene deletions) were observed, causing a diffuse skin rash. Such allergic reactions typically indicate progression to potentially serious nephrotic syndrome. A unique immunotolerance regimen of oral oxatomide and intravenous hydrocortisone was started to proactively prevent allergic reactions in this patient during rFIXFc prophylaxis. Even though low titers of the inhibitor (0.6-1.0 Bethesda units) were observed occasionally during subsequent follow-up, there were no signs of further allergies or development of nephrotic syndrome.
Conclusion: This is an uncommon case in which rFIXFc was continued despite the appearance of an allergic reaction and the development of FIX inhibitors. Subsequent allergic reactions were prevented with a combination of oral oxatomide and intravenous hydrocortisone given prior to prophylactic rFIXFc. Further studies are recommended to determine the usefulness of this combination with rFIX therapy.
Keywords: Case report; Coagulation factor IX; Hemophilia B; Intracranial hemorrhage; rFIX.
© 2024. The Author(s).