Source / episode info
- **Episode:**382
- **Title:**Divine Intervention Episode 382 – USMLE Step 2CK/3 Rapid Review Series 73
- **Published:**2022-04-05
- Source:Episode page
One-liner
This episode provides a rapid review comparing key enzyme deficiencies (G6PD, NADPH oxidase) and toxicological states (cyanide poisoning, methemoglobinemia), emphasizing the distinct lab findings, pathophysiology, and management of hemolytic anemia, metabolic acidosis, and aminoacidopathies.
High-yield summary
- G6PD Deficiency: Hemolysis triggered by oxidative stress (e.g., nitrates, primaquine). Classic triad: decreased Haptoglobin, increased indirect bilirubin, and bite cells on smear.
- Cyanide Poisoning: Causes cellular hypoxia by inhibiting cytochrome oxidase (Complex IV), leading to mandatory reliance on anaerobic glycolysis and resulting in a high anion gap metabolic acidosis (lactic acidosis). Hb levels are typically normal.
- Methemoglobinemia: A qualitative defect where iron is oxidized from Fe(II) to Fe(III), impairing oxygen carriage. Patients are hypoxic but have normal hemoglobin concentration. Treated with Methylene Blue.
- CGD: Caused by NADPH oxidase deficiency, leading to impaired oxidative burst and recurrent infections, particularly with catalase-positive organisms (e.g., Staphylococcus, Aspergillus). Treatment involves Interferon gamma.
- MSUD: Deficiency of branched-chain ketoacid dehydrogenase leads to the accumulation of branched amino acids (leucine, isoleucine, valine), presenting with a characteristic sweet odor in urine/sweat. Management requires dietary restriction.
Learning objectives
- Differentiate between causes of hemolytic anemia (e.g., G6PD deficiency vs. autoimmune hemolysis).
- Recognize the metabolic consequences and treatments for various toxic exposures (cyanide, methemoglobinemia).
- Identify the key enzyme deficiencies associated with aminoacidopathies (MSUD) and immunodeficiencies (CGD).
- Understand the pathophysiology of oxidative stress in red blood cells and phagocytes.
- Correlate clinical findings (e.g., sweet odor, cyanosis, hemolysis) with specific metabolic or enzymatic defects.
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