A 65-year-old man presents to the clinic with complaints of fatigue, difficulty walking, and memory problems that have been progressively worsening over the past 6 months. He also reports numbness and tingling in his hands and feet. His past medical history is significant for type 2 diabetes which is managed with metformin. He lives alone and has a history of alcohol use, consuming approximately 3-4 drinks per day for the past 20 years. His vital signs are: temperature 98.4°F (36.9°C), heart rate 88 beats/minute, blood pressure 130/78 mmHg, and respirations 16/minute. Neurological examination reveals decreased vibration and position sense in his lower extremities, and his gait is ataxic. Laboratory tests reveal a hemoglobin A1c of 6.8%, a hemoglobin level of 10.2 g/dL, and a mean corpuscular volume (MCV) of 110 fL. Further testing shows elevated methylmalonic acid and homocysteine levels.
Which of the following is the most likely diagnosis?
The correct answer is:
B) Iron deficiency anemia
Vitamin B12 deficiency presents with megaloblastic anemia and characteristic neurological symptoms, including peripheral neuropathy, loss of position and vibration sense, ataxia, memory impairment, and subacute combined degeneration of the spinal cord. Elevated methylmalonic acid and homocysteine levels are diagnostic markers for vitamin B12 deficiency. The patient's symptoms, laboratory findings, and elevated methylmalonic acid and homocysteine levels are consistent with vitamin B12 deficiency. His history of alcohol use may contribute to nutritional deficiencies, including vitamin B12 deficiency.
Answer choice A: Folate deficiency, is incorrect. While folate deficiency can also cause megaloblastic anemia, it does not typically cause neurological symptoms or elevated methylmalonic acid levels.
Answer choice B: Iron deficiency anemia, is incorrect. Iron deficiency anemia presents as microcytic anemia, not megaloblastic anemia, and does not cause neurological symptoms.
Answer choice C: Sideroblastic anemia, is incorrect. Sideroblastic anemia is a microcytic anemia and does not present with elevated methylmalonic acid or neurological symptoms.
Answer choice D: Thalassemia minor, is incorrect. Thalassemia minor is a microcytic anemia and does not cause elevated methylmalonic acid or neurological symptoms.
Key Learning Point
Vitamin B12 deficiency presents with megaloblastic anemia and neurological symptoms, with elevated methylmalonic acid and homocysteine levels serving as diagnostic markers.
