Source / episode info

• **Episode:**480
• **Title:**Divine Intervention Episode 480: USMLE Step 2/3 Rapid Review Series 101
• **Published:**2023-08-31
• Source:Episode page

One-liner

This rapid review series emphasizes synthesizing multiple clues to diagnose metabolic disorders (Lesch-Nyhan Syndrome, PKU), urological malignancies (Renal Cell Carcinoma), and differential diagnoses for tick-borne illnesses (Anaplasmosis, Babesiosis, Lyme Disease).

High-yield summary

• Lesch-Nyhan Syndrome (LNS): An X-linked recessive disorder caused by a deficiency in the enzyme HGPRT (Hypoxanthine Guanine Phosphoribosyltransferase), leading to purine salvage pathway failure, hyperuricemia, gout, and characteristic self-mutilating behavior. It is exclusively seen in males.
• Renal Cell Carcinoma (RCC): High suspicion when a patient presents with the triad of advanced age, unexplained weight loss, and hematuria, especially with a history of heavy smoking (e.g., 120+ pack years). The biopsy specimen must be the entire kidney via nephrectomy/exfferectomy, not just the mass.
• Phenylketonuria (PKU): A metabolic disorder caused by deficiency in PAH (Phenylalanine hydroxylase), leading to the inability to convert phenylalanine to tyrosine. Management requires lifelong dietary restriction of phenylalanine and supplementation with tyrosine.
• Tick-borne Differential: Differentiating Anaplasmosis, Babesiosis, and Lyme disease relies on geography, clinical presentation, and blood smear findings: Babesia (New England, red cells only, Maltese cross); Anaplasma (Midwest/Wisconsin, morulae in cytoplasm); Lyme (New England).
• Predictive Reasoning: Board questions often require combining multiple clues (e.g., age + weight loss + hematuria) to narrow the differential diagnosis before even seeing the histology.

Learning objectives

• Differentiate the genetic basis and clinical manifestations of Lesch-Nyhan Syndrome from other metabolic disorders.
• Recognize the classic risk factors and diagnostic workup for Renal Cell Carcinoma, including appropriate biopsy techniques.
• Understand the biochemical pathway disrupted in PKU and identify the correct amino acid supplementation strategy.
• Distinguish between Anaplasmosis, Babesiosis, and Lyme disease based on geography, target cells (RBCs vs WBCs), and peripheral blood smear findings.
• Apply inductive reasoning by synthesizing multiple clues (age, history, symptoms) to narrow a differential diagnosis in complex board vignettes.

Board exam buzzwords