Overwhelming post-splenectomy Capnocytophaga canimorsus infection complicated by suspected infection-associated secondary thrombotic microangiopathy with a complement-mediated hemolytic uremic syndrome phenotype and extensive tissue necrosis after a dog bite

Abstract

Capnocytophaga canimorsus is a rare zoonotic pathogen that can cause fulminant sepsis in asplenic patients, including overwhelming post-splenectomy infection after dog bites. Its association with suspected infection-associated secondary thrombotic microangiopathy with a complement-mediated hemolytic uremic syndrome phenotype and the subsequent need for complex reconstructive surgery has rarely been reported. This case illustrates a distinctive clinical course characterized by sequential infectious, hematologic, and ischemic complications requiring phase-specific management. A 32-year-old woman with a history of childhood total splenectomy, known at the time of emergency department presentation, developed fever, nausea, and abdominal pain 2 days after sustaining superficial hand dog bites. The clinical presentation was consistent with Capnocytophaga canimorsus -associated overwhelming post-splenectomy infection (OPSI). She rapidly progressed to septic shock with disseminated intravascular coagulation and multiorgan failure. Blood cultures grew Capnocytophaga canimorsus . Despite initial control of the infection, persistent thrombocytopenia, microangiopathic hemolytic anemia, acute kidney injury, and ongoing organ dysfunction raised suspicion of infection-associated secondary thrombotic microangiopathy with a complement-mediated hemolytic uremic syndrome phenotype. Empiric eculizumab was initiated after multidisciplinary discussion and was followed by progressive hematologic and hemodynamic improvement over the subsequent days, alongside antimicrobial therapy, transfusion and coagulation support, continuous renal replacement therapy, and improvement of sepsis-associated DIC. The clinical course was complicated by extensive ischemic necrosis of all four extremities and the nose, necessitating staged reconstructive surgical interventions. At follow-up, the patient had returned home with preserved cognitive function but limited mobility requiring physical assistance. This case underscores the importance of early recognition of Capnocytophaga canimorsus infection in high-risk patients and highlights the need to consider infection-associated secondary thrombotic microangiopathy with a complement-mediated hemolytic uremic syndrome phenotype when thrombocytopenia, microangiopathic hemolysis, kidney failure, and organ dysfunction persist despite improvement of infection and DIC. Timely multidisciplinary, pathophysiology-guided interventions can be lifesaving, although substantial long-term disability may still occur.