Case Presentation: A 39-year-old male with no past medical history presented with four days of a constant “pins and needles” sensation located from fingertips through elbows bilaterally as well as progressive shortness of breath and fatigue. He reported feeling unbalanced and light-headed. Additionally, for seven months he experienced confusion including word finding difficulties. Further history revealed a strict vegan diet for 20 years with no vitamin supplementation. Vital signs were notable for blood pressure 85/48 mmHg, heart rate 60 bpm, and normal oxygen saturation. Physical exam showed sublingual pallor and slow conversational speech. Laboratory results revealed pancytopenia with white blood cell count 1.7k/mcL, hemoglobin 4.5 gm/dL, mean corpuscular volume 103 fL and platelets 111k/mcL. Indirect bilirubin was elevated 1.74 mg/dL with a low reticulocyte index 0.1, elevated lactate dehydrogenase >3600 unit/L, and low haptoglobin < 3 mg/dL. Vitamin B12 level was undetectable at <50 pg/mL and normal folic acid. Thorough infectious and autoimmune workups including syphilis, HIV, viral hepatitis, EBV, Parvovirus, and systemic lupus erythematous were unremarkable. Intrinsic factor and parietal cell antibodies were negative. Imaging studies were unrevealing. During his hospital stay, he received three units of packed red blood cells and two subcutaneous doses of 1000 mcg B12 with rapid improvement in his mental status and paresthesia. He was discharged with parenteral B12 supplementation.

Discussion: Anemia related to B12 (cobalamin) deficiency is most frequently due to pernicious anemia and less commonly as a result of dietary deficiency. Vitamin B12 is an important cofactor in DNA and RNA synthesis found in animal products. A deficiency leading to clinical consequences typically takes one to four years to develop. Patients can develop pancytopenia and neurologic consequences. Laboratory work is consistent with hemolysis, and in this case, represents ineffective erythropoiesis which results in intramedullary hemolysis where poorly formed erythropoietic cells are phagocytosed in the bone marrow. Unlike other causes of hemolytic anemia, the reticulocyte count and index is low in B12 deficiency, consistent with a hypoproliferative state and poor marrow response. Subacute combined degeneration is the most feared neurologic sequelae and is characterized by demyelination of the dorsal, lateral, and spinocerebellar tracts of the spinal cord. Common effects include sensory deficits, paresthesia, weakness, ataxia, and gait disturbance, while severe cases cause spasticity and paraplegia. Recovery from neurologic symptoms typically takes several months after B12 supplementation and in some cases are permanent. It was important to consider alternative etiologies such as malignancy, rheumatologic, and infectious in the preliminary workup.

Conclusions: Ultimately, the key history finding of a strict vegan diet and unrevealing secondary workup allowed for the diagnosis and treatment of vitamin B12 deficiency. Luckily, our patient’s symptoms of mental fog, ataxia and paresthesia improved rapidly with supplementation. This case highlights the importance of vitamin B12 supplementation for patients following a strict vegan or vegetarian diet.