A patient with pernicious anemia

A young man with anemia had paresthesiae of his feet and difficulty in walking. Investigations revealed that he had a macrocytic anemia due to Vitamin B12 deficiency. 

Pernicious anemia is due to Vit B12 deficiency. This is a macrocytic anemia with a megaloblastic reaction in the bone marrow. Patients with pernicious anemia can also have pancytopenia because of defective cell formation in the bone marrow. Neurological disorders involving the spinal cord, peripheral nerves and sometimes the brain are what gives this anemia the adjective 'pernicious' which means dangerous. The neurological complications of Vit B12 deficiency can occur without the anemia and anemia can be present without the neurological complications.

Pernicious anemia is often associated with gastric atrophy and hypochlorhydria which leads to poor iron absorption and associated iron deficiency. Gastric atrophy increases the risk of gastric adenocarcinoma in patients with pernicious anemia.

Autoantibodies directed against the gastric parietal cells and the intrinsic factor produced by these parietal cells are the usual cause of pernicious anemia. These patients are therefore at increased risk of other autoimmune diseases involving the thyroid, pancreas and adrenal glands.

Serum LDH levels are useful in diagnosis because they are elevated in patients with haemolytic anemia. Once the diagnosis is made, treatment is started with either cyanocobalamin or hydroxocobalamin. These are given as injections subcutaneously or intramuscularly until the desired response is achieved. Maintenance doses of Vit B12 need only be given once a month because the body requires very low amounts of Vit B12 per day (1ug per day). It may also be possible for maintenance doses of Vit B12 to be given orally in high daily doses because, even without intrinsic factor, about 1 percent of Vit B12 is absorbed from the gut.

People at risk of pernicious anemia are those who do not consume either meat or milk because the natural source of Vit B12 is from these two dietary products.

Data published by the Institute of Medical Research in 1994 (article) gives us an idea of the prevalence of Vitamin B12 deficiency in Malaysia. In the year 1993 to 1994 it was around 8.2 percent (based on a sample of around 9000 patients who were suspected to have Vit B12 deficiency). 

Macrocytic anemia can also be due to folic acid deficiency. Folic acid deficiency can cause cognitive changes, depression, dementia and rarely the spinal cord and peripheral nerve damage of Vitamin B12 deficiency. Both folic acid and Vitamin B12 are therefore important vitamins for the blood and nervous system (article).