DIP Episode 420 - USMLE Step 2/3 Rapid Review Series 85

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**Episode:**420
**Title:**Divine Intervention Episode 420: USMLE Step 2/3 Rapid Review Series 85
**Published:**2022-10-20
Source:Episode page

One-liner

This episode reviews Parvovirus B19 infection (aplasic crisis), the complex metabolic picture of Van der Wiele syndrome (hyperinsulinemia triad), and high-yield pitfalls in renal physiology related to ACE inhibitor use and renal artery stenosis.

High-yield summary

Parvovirus B19: Causes a characteristic "slapped cheek" rash; testing is crucial in adults who work with children (e.g., daycare workers). In hemolytic anemias, it can trigger an aplastic crisis by damaging red blood cell precursors, leading to absent reticulocytosis.
Van der Wiele Syndrome (VWS): An overgrowth disorder characterized by hyperinsulinemia, which leads to a metabolic triad: 1) Hypocalcemia (calcium shift), 2) Seizures/Tetany, and 3) Hypokalemia (via increased Na+/K+ ATPase activity).
ACE Inhibitors & Electrolytes: ACE inhibitors cause minor bumps in K+ and mild metabolic acidosis due to reduced Angiotensin II stimulation of aldosterone. Hyperkalemia and metabolic acidosis are classic side effects, but massive electrolyte shifts suggest renal artery stenosis.
Renal Artery Stenosis Trap: In RAS, the body relies heavily on efferent arteriolar tone (maintained by Ang II) to maintain GFR. Blocking this tone with an ACEi/ARB can cause a disproportionate drop in GFR and creatinine.

Learning objectives

Identify the clinical manifestations and associated complications of Parvovirus B19 infection.
Recognize the metabolic triad associated with Van der Wiele syndrome and its underlying pathophysiology (hyperinsulinemia).
Understand the mechanism by which ACE inhibitors affect potassium, acid-base balance, and glomerular filtration rate (GFR).
Differentiate between expected electrolyte changes from RAAS blockade versus those indicating severe renal artery stenosis.

Board exam buzzwords

Condition	Key Finding	Association	Board Exam Tip
Parvovirus B19	"Slapped cheek" rash; Aplastic crisis	Hemolytic anemia (e.g., SCD, Hereditary Spherocytosis)	Always consider B19 in hemolytic patients presenting with cytopenias/anemia.
Van der Wiele Syndrome	Hyperinsulinemia; Hypocalcemia; Hypokalemia	Overgrowth disorder; Seizures; Muscle weakness	The triad of metabolic abnormalities is the most critical association to memorize.
ACE Inhibitors (ACEi)	Hyperkalemia, Metabolic Acidosis, Minor GFR bump	RAAS blockade; Reduced Ang II -> Aldosterone/H+ retention	Remember that major electrolyte shifts suggest a pre-existing renal issue like stenosis.
Renal Artery Stenosis	Disproportionate drop in GFR after ACEi initiation	Loss of efferent arteriolar tone maintenance by Angiotensin II	If the change is massive, suspect RAS first.

Source / episode info

One-liner

High-yield summary

Learning objectives

Board exam buzzwords

Rapid review table