Vitamins B9 and B12 Deficiencies
Megaloblastic anemia is a macrocytic anemia that is usually caused by either a Vitamin B9 or Vitamin B12 Deficiency.
These vitamin deficiencies are characterized by the presence of hypersegmented neutrophils in the peripheral blood, in addition to elevated homocysteine levels (see Homocysteine metabolism - coming soon!). Despite these similarities, there are a number of distinguishing characteristics between folate and cobalamin deficiency.
Vitamin B12 Deficiency is characterized by neurologic symptoms, as myelin is affected in a process known as subacute combined degeneration. Specifically, the lateral corticospinal tract, spinocerebellar tract, and dorsal columns are affected. Labs will show elevated methylmalonic acid (MMA) levels, a finding not observed in folate deficiency.
Contrastingly, Vitamin B9 Deficiency is more common and occurs faster than B12 deficiency, as the liver has a smaller reserve pool of folate. Folate deficiency is common in alcoholics, and is often seen in conjunction with Vitamin B1 (Thiamine) Deficiency.
Find Vitamin B9 and B12 Deficiency and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.