Unmasking Vitamin B12 Deficiency Misdiagnosed as Myelodysplastic Syndrome

Background: Pancytopenia is characterized by a decrease in all three types of blood cells. Instead of being a standalone disease, it acts as a common outcome resulting from various factors, including infections, autoimmune disorders, genetic issues, nutritional deficiencies, and malignancies. Pinpointing the root cause of pancytopenia poses a challenge but is essential for devising an effective treatment plan and predicting the likely prognosis. Vitamin B12 deficiency is a common cause of megaloblastic anemia, pancytopenia, and various neuropsychiatric symptoms. However, diagnosing vitamin B12 deficiency lacks a definitive gold standard. Case Presentation: We present two cases where patients initially exhibited pancytopenia with seemingly normal vitamin B12 levels. Based on a bone marrow biopsy, they were initially diagnosed with myelodysplastic syndrome (MDS). Subsequent investigations revealed elevated serum methylmalonic acid (MMA) levels, leading to a revised diagnosis of vitamin B12 deficiency. Both patients showed positive responses to adequate vitamin B12 supplementation. Conclusion: Our case series highlights the importance of ruling out alternative causes of dysplasia in MDS when solely morphological abnormalities are observed on a bone marrow biopsy. It also underscores the crucial aspect of assessing MMA and homocysteine levels in individuals with normal vitamin B12 levels when there is a high clinical suspicion of B12 deficiency.