31st July 2023

Pernicious Anaemia

Describes autoimmune destruction of gastric parietal cells that secrete intrinsic factor, reducing vitamin B12 absorption. B12 is key in the erythropoiesis and in myelination of neurons, leading to the clinical features. Pernicious anaemia is the most common cause of B12 deficiency; the differential includes dietary deficiency (especially seen in vegans), disease of the terminal ileum (e.g., Crohn’s disease) or previous gastrectomy.

Pernicious anaemia is strongly associated with other autoimmune conditions; thus, a thorough past medical history and family history is required. The associations, clinical features and investigations are summarised in Table 1. The condition is rare in those <40 years old. Diagnosis is usually made with positive autoantibodies following clinical suspicion.

Table 1: Associations, clinical features and investigations for pernicious anaemia.

Management involves B12 replacement in the form of intramuscular hydroxocobalamin. If there are no neurological features, 3 injections per week are given for the first 2 weeks, followed by injections once every 3 months. The 1mg doses are given more frequently if neurological features are present; contact the haematology team for an appropriate regimen.

Schematic showing normal absorption of vitamin B12 from the diet. In pernicious anaemia, there is reduced or absent intrinsic factor secretion; therefore, much less vitamin B12 is absorbed at the terminal ileum.