Source / episode info
- **Episode:**456
- **Title:**Divine Intervention Episode 456: USMLE Step 2/3 Rapid Review Series 95
- **Published:**2023-05-03
- Source:Episode page
One-liner
This episode provides a rapid review of high-yield topics including mitochondrial inheritance patterns (maternal transmission only), ezetimibe lipoproteinemia due to MTP mutations, multiple mechanisms causing hypercalcemia (Sarcoidosis, MM, PTHrP), and critical infectious disease management for Listeria in neonates and immunocompromised adults.
High-yield summary
- Mitochondrial Disorders: Inheritance is strictly maternal; symptoms can vary widely due to heteroplasmy (unequal number of mitochondria/mutant mtDNA copies across different cells). Clinical signs include lactic acidosis, stroke-like episodes, and ragged red fibers on muscle biopsy.
- Ezetimibe Lipoproteinemia: Caused by mutations in the Microsomal Transfer Protein (MTP) gene, preventing assembly of lipoproteins. Leads to malabsorption of dietary fats and fat-soluble vitamins (A, D, K, E). Key findings include low cholesterol, acanthocytosis (Vit E deficiency), coagulopathy (Vit K deficiency), and secondary hyperparathyroidism/hypophosphatemia (Vit D deficiency).
- Hypercalcemia Management: The first step in symptomatic hypercalcemia is always volume expansion (IV fluids). In the hospital setting, malignancy (e.g., Multiple Myeloma, Renal Cell Carcinoma) is the most likely cause.
- Sarcoidosis Hypercalcemia: Occurs because granulomas contain activated macrophages that produce 1--hydroxylase, converting calcidiol to active Vitamin D ({CaD}_2).
- Listeria monocytogenes: High risk in neonates and immunocompromised adults (especially those on TNF inhibitors). Treatment requires ampicillin coverage.
Learning objectives
- Differentiate the inheritance patterns of mitochondrial disorders.
- Recognize the clinical triad associated with MTP mutations/Ezetimibe lipoproteinemia.
- Identify the mechanisms leading to hypercalcemia in sarcoidosis, multiple myeloma, and PTHrP excess.
- State the initial management steps for symptomatic hypercalcemia.
- Determine the appropriate antibiotic coverage for Listeria meningitis in neonates and immunocompromised adults.
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