Unmasking Vitamin B12 Deficiency Misdiagnosed as Myelodysplastic Syndrome.

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. 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. 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.