Psychiatric manifestations of vitamin B12 deficiency:
(1) moderate to severe depression
(2) delusions including psychosis
(3) hypomania or hypermania
(4) mood lability
(5) mental confusion ranging from mild to dementia
(6) memory loss
When to be suspected:
(1) elderly patient with no previous psychiatric history
(2) nutritional problems
(3) markers of vitamin B12 deficiency (low serum vitamin B12, elevated methylmalonic acid, elevated homocysteine)
(4) anemia, which may be megaloblastic or normocytic (if mixed with iron deficiency)
(5) abnormal reflexes
(6) autoimmune disease (antibodies to parietal cells or intrinsic factor, autoimmune thyroiditis)
The diagnosis is supported if there is reversal of psychiatric findings with vitamin B12 therapy.
