In the present report, we describe the case of a 19-year-old woman who presented with diffuse abdominal pain and severe anemia. At admission, she presented with life-threatening medical conditions due to severe anemia and critical abdominal features. Her medical history was unremarkable. Findings on clinical images and laboratory parameters were consistent with an acute and severe hemolytic disorder; her Hb level had decreased to 3.9 g/dL, whereas the reticulocyte count, indirect bilirubin level, and lactate dehydrogenase concentration were elevated. On admission, the patient was transfused with packed red blood cells (12 units). A strongly positive result on direct antiglobulin test (IgG3 and C3d) was detected; the indirect antiglobulin test indicated a positive result at 4℃ and a negative result at 22℃ and 39℃ in the presence of a cold panagglutinin antibody (IgM). The concomitant acute abdominal condition was investigated by a comprehensive radiological work-up, including an abdominal echography and a body computed tomography scan, and revealed complete thrombosis of the portal and splenic veins as well as partial occlusion of the superior mesenteric vein. A diagnosis of mixed AIHA associated with SVT was made, and treatment with prednisone (1 mg/kg body weight/day) was promptly initiated; in addition, therapeutic subcutaneous Fraxiparine injections with warfarin were also administered. Additional laboratory investigations revealed no other causes of anemia and ruled out the presence of autoimmune disorders, infections, and liver diseases. Investigations into the possible causes for the development of the thrombosis, including all genetic and acquired abnormalities associated with hypercoagulability states, as well as those aimed to identify a possible underlying neoplastic etiology, did not provide any useful findings. Similarly, the presence of a paroxysmal nocturnal hemoglobinuria clone or abnormal Hb chains was ruled out.

The patient was discharged with continued warfarin treatment with a fraxiparine bridge. However, based on the patient's decision, the warfarin treatment was subsequently discontinued, whereas the fraxiparine was maintained for only 6 months, after which a careful reevaluation showed complete SVT resolution and full vein recanalization in the splanchnic area. Moreover, based on the clinical response, the prednisone dose was adjusted and tapered until the minimal effective maintenance dose was reached; immunohematological evaluations were regularly repeated and indicated completely negative results. However, an AIHA recurrence was observed 6 months after the reduction of prednisone to the lowest dosage. At this time, a second line treatment of rituximab (375 mg/m², 4 weekly courses) was given. A complete response by rituximab was achieved. At approximately 1 year after the primary diagnosis was made, the patient is doing well. As AIHA and acute SVT may have been the initial manifestations of underlying occult disorders, the patient is carefully and regularly evaluated to promptly diagnose any recurrence of her hematological complaints. Thus, we report a rare and unexplained association of primary mixed AIHA with acute SVT, both of idiopathic origin that simultaneously occurred in a young patient.