Due to malabsorption of B12.
Usually from small bowel disease, gastric resection or genetic malabsorption problem.
Clinical features – weakness, tiredness, dyspnoea, parathesia, painful red tongue, dementia, diarrhoea; GI symptoms; neuropathy
Schilling test of decreased absorption of B12 is positive; RBC indices show increased MCV.
Treatment – parenteral replacement with cyanocobalamin monthly for rest of life.