Addisonian pernicious anaemia
anaemia due to deficiency of vitamin b12, most commonly as a result of failure to absorb the vitamin from the diet. There is release into the circulation of immature precursors of red blood cells, the same type of megaloblastic anaemia as is seen in folic acid deficiency. There is also progressive irreversible damage to the spinal cord (sub-acute combined degeneration).The underlying cause of the condition may be the production of antibodies against either the intrinsic factor that is required for absorption of the vitamin, or the cells of the gastric mucosa that secrete intrinsic factor. Atrophy of the gastric mucosa with ageing also impairs vitamin B12 absorption,and causes pernicious anaemia. Dietary deficiency of vitamin B12 may occur in strict vegetarians (vegans).