Pernicious anemia is severe anemia most often affecting older adults, caused by failure of the stomach to absorb vitamin B12 and characterized by abnormally large red blood cells, gastrointestinal disturbances, and lesions of the spinal cord. Pernicious anemia is caused by a lack of intrinsic factor and could be an autoimmune disorder. The identification of various autoantibodies helps in the confirmation of the diagnosis and hence towards the patient management. In such patients, oral supplements or intramuscular injections of vitamin B12 are indicated.

Pernicious anaemia is the most common cause of cobalamin deficiency. Nervous disorders associated with cobalamin deficiency are neuropathy, optic atrophy, dementia and myelopathy (subacute combined degeneration). In this case, symptoms are those of posterior and lateral column dysfunction of the spinal cord, with diminished vibratory sensation, ataxia, weakness of limbs, hyperreflexia, extensor plantar response and spasticity. Macrocytosis and anaemia are often lacking. There is an inverse correlation between the degree of anaemia and the extent of nervous impairment. The most sensitive tool for the diagnosis of cobalamin deficiency is the serum cobalamin level. But a normal cobalamin assay does not fully exclude cobalamin deficiency. Levels of serum methylmalonic acid and total homocysteine are useful as ancillary tests in the diagnosis. Treatment is based on intramuscular injections of vitamin B12.