Case Presentation: A previously healthy 27-year-old man presented with one week of generalized weakness and lightheadedness upon standing. He works in construction (installing fireplaces) but had been unable to work during the last week due to symptoms. On presentation, he was tachycardic with HR 120; vital signs were otherwise normal. Exam was notable for significant pallor. No hepatosplenomegaly, lymphadenopathy, or signs of bleeding. Initial labs were notable for WBC count 1.0 (absolute neutrophil count 420), hemoglobin 2.6, platelets 32, INR 1.3. Mean corpuscular volume (MCV) unable to be measured due to severe anemia. Total bilirubin was 1.6 with direct bilirubin 0.3. Lactate dehydrogenase (LDH) was 3305 (upper limit of normal 250 U/L), and direct antiglobulin test (DAT) was positive with positive IgG and C3d. Additional labs revealed haptoglobin < 10 and reticulocyte percent 5.9%. Peripheral blood smear showed severe macrocytic anemia with occasional schistocytes and polychromasia, severe leukopenia, and thrombocytopenia. Infectious workup, including fungal serologies, was negative. Patient received 2 units packed RBCs with appropriate response in hemoglobin. Ultimately, vitamin B12 resulted as undetectable (< 150 pg/mL), and patient was started on daily intramuscular vitamin B12.Patient was discharged with daily oral and weekly intramuscular Vitamin B12 supplementation with close follow up with hematology. Intrinsic factor blocking antibody returned positive after discharge, consistent with pernicious anemia. Two weeks after discharge, repeat labs showed resolution of pancytopenia. LDH had decreased, indicating improvement in hemolysis. Repeat DAT was negative.
Discussion: Vitamin B12 deficiency is relatively common in the United States, affecting approximately 5% of adults under 60 years old, with increased prevalence in older adults. This patient presented with severe pancytopenia with neutropenia and evidence of warm autoimmune hemolytic anemia (AIHA). Investigation revealed vitamin B12 deficiency secondary to pernicious anemia, which is an uncommon cause of vitamin B12 deficiency in young adults. Macrocytic anemia is a well-known manifestation of B12 deficiency, but other hematologic abnormalities can occur.Pancytopenia, neutropenia, and AIHA are rare hematologic manifestations of severe vitamin B12 deficiency. The differential for new-onset pancytopenia is broad and includes genetic, malignant, autoimmune, infectious, and nutritional etiologies. Severe pancytopenia in this previously healthy patient initially raised concern for hematologic malignancies or other disorders of impaired hematopoiesis. This patient was ultimately diagnosed with a reversible condition, and vitamin B12 replacement led to rapid resolution of patient’s severe anemia, neutropenia, and hemolysis.This case describes an uncommon presentation of a common condition, highlighting the importance of considering B12 deficiency in a variety of clinical presentations.
Conclusions: Vitamin B12 deficiency is a common condition that can rarely lead to severe hematologic abnormalities, which can mimic life-threatening conditions like hematologic malignancies. It is important that hospitalists recognize vitamin B12 deficiency as a possible etiology of pancytopenia, neutropenia, and AIHA. Vitamin B12 deficiency is a reversible condition, and timely identification can aid in early diagnosis and treatment, as well as potentially avoiding unnecessary investigations.