SM_250b: Megaloblastic Anemias Flashcards
These are ____
Megaloblasts in bone marrow
Megaloblasts result from ___
Megaloblasts result from defective DNA synthesis
Describe consequences of megaloblastosis
Consequences of megaloblastosis
- Bone marrow: ineffective erythropoiesis: hypercellular marrow, increase in bilirubin and LDH and decrease in haptoglobin because contents of cytoplasm released
- Peripheral blood: macro-ovalocytes (increased average RBC size), neutrophil hypersegmentation
Megaloblastic anemia most commonly results from ____ or ____
Megaloblastic anemia most commonly results from Vitamin B12 deficiency or folic acid deficiency
Describe the intersection of B12 and folate metabolism
Intersection of B12 and folate metabolism
- Vitamin B12 accepts methyl group from methyltetrahydrofolate -> methylates homocysteine to generate methionine -> provides tetrahydrofolate required for folate coenzymes that aid in purine and pyrimidine synthesis and thymidylate for DNA synthesis
- Hydrogen transfer: generation of succinyl CoA from methylmalonyl CoA
Vitamin B12 deficiency leads to ___ and ___
Vitamin B12 deficiency leads to
- Increase in homocysteine due to impaired methyl transfer
- Increase in methylmalonic acid
Describe Vitamin B12 absorption
Vitamin B12 absorption: meat, eggs, dairy (3-5 ug)
- Gastric acid liberates B12 from binding proteins
- Binding to salivary HC
- Duodenum: pancreatic proteases release B12 from HC
- Intrinsic factor secreted by gastric parietal cells and binds B12
- IF-B12 complex bound in ileum (cubam receptor)
- Bound to TCII and distributed
Robust liver stores
Describe causes of Vitamin B12 deficiency
Vitamin B12 deficiency
- Malabsorption >>> dietary deficiency
- Gastric disease: acid poor environment, surgery, lack of intrinsic factor
- Pancreatic disease
- Intestinal disorders: IBD, bacterial overgrowth, celiac, malignancy
Pernicious anemia is ___
Pernicious anemia is an autoimmune illness in which autoantibodies destroy gastric parietal cells, leading to deficient HCl production
- Antiboides that bind intrinsic factor
- Often see in older adults
- Can exist with other autoimmune illness
- Association with malignancy (gastric cancer and carcinoid tumors)
Pernicious anemia leads to ___ and ___
Pernicious anemia leads to ineffective erythropoiesis and subacute combined degeneration
- Ineffective erythropoiesis: anemia, thrombocytopenia, leukopenia, hemolysis (LDH, increased bilirubin)
- Subacute combined degeneration: brain and cranial nerves (dementia and personality change), neuropathy (loss of vibratory and position sense, abnormal sensations of hands and feet)
Describe clinical and laboratory findings suggestive of Vitamin B12 deficiency
Vitamin B12 deficiency
- PNS and CNS disease
- Low serum B12 levels (< 200 pg/mL)
- Increased methylmalonic acid
- Increased homocysteine
- Anti-parietal and/or intrinsic factor antibodies (serum gastrin may also be increased)
Describe treatment of Vitamin B12 deficiency
Vitamin B12 deficiency treatment
- Underlying cause of possible
- Intramuscular or high dose oral treatment
- Lifelong treatment when cause unknown or irreversible
- Therapy not always appropriate
Vitamin B12 clinical presentation varies from ___ to ___
Vitamin B12 clinical presentation varies from severe anemia without neurologic symptoms to predominantly neurologic presentations with mild/no anemia
Folic acid comes from ____ but the body stores ____
Folic acid comes from leafy green vegetables but the body stores minimal
- Absorption in small intestine
- Byproducts taken up by liver and can be recycled into bile for gut reabsorption (enterohepatic circulation)
Describe causes of folate deficiency
Folate deficiency causes
- Dietary: poor diet, chronic alcoholism
- Increased requirements: hemolytic anemia, pregnancy
- Malabsorption (small intestinal disorders): celiac disase, IBD
- Metabolic block in utilization: dihydrofolate reductase inhibitors (methotrexate, trimethoprim)
- Loss: hemodialysis
Describe clinical features of folate deficiency
Folate deficiency clinical features
- Megaloblastic anemia identical to that produced by Vitamin B12 deficiency
- Neither combined system neurologic disease nor specific neuropathy
- Dietary deficiency state usually in setting of general malnutrition so other clinical features usually present
- NTDs in pregnancy
Describe diagnosis of folate deficiency
Folate deficiency diagnosis
- Serum folate levels < 2 ng/mL: sensitive to recent intake, acute EtOH binge can result in low levels
- RBC folate levels < 280 nm/L: reflects chronic folate status, can be low in Vitamin B12 deficiency
- Elevated serum homocysteine
Describe treatment for folate deficiency
Folate deficiency treatment
- Oral folic acid: 1-5 mg daily (easily absorbed)
- Prophylactic treatment in patients with high demand
- Must exclude Vitamin B12 deficiency: folate supplementation can improve anemia but will not correct neurologic manifestations
Compare Vitamin B12 and folate deficiencies
Vitamin B12 and folate deficiencies
Describe other causes of macrocytosis
Other causes of macrocytosis (MCV > 100)
- Alcohol
- Liver disease
- Hypothyroidism
- Bone marrow failure states (aplastic anemia, myelodysplastic syndrome)
- Reticulocytosis
- Drugs (hydroxyurea, anti-retrovirals), artifact
Describe clinical manifestations of copper deficiency
Copper deficiency
- Macrocytic anemia (also neutropenia)
- Bone marrow findings can mimic myelodysplastic syndromes
- Neurologic symptoms: ataxia, neuropathy
- Fragile hair, depigmentation
- Edema
- Osteoporosis
- Risk factors: gastric bypass (absorbed in stomach and small intestine), celiac disease, excess zinc ingestion, and total parenteral nutrition
___ is treatment for copper deficiency
Copper supplementation is treatment for copper deficiency
