DIP Episode 355 - USMLE Step 2CK/3 Rapid Review Series 67

Source / episode info

• Episode: 355
• Title: Divine Intervention Episode 355 – USMLE Step 2 CK/3 Rapid Review Series 67
• Published: 2021-12-03
• Source: Episode page

One-liner

This episode reviews the management of Herpes Zoster with acyclovir and nephrolithiasis risk; details the workup of resistant hypertension using PAC/PRA ratio to differentiate primary hyperaldosteronism from renal artery stenosis or fibromuscular dysplasia; and covers the diverse causes and clinical implications of gynecomastia.

High-yield summary

• Herpes Zoster: Vesicular lesions on an erythematous base with sharp, pink borders suggest Herpes Zoster (shingles). Treatment requires antiviral agents like acyclovir, which function as false nucleotides inhibiting DNA synthesis.
• Nephrolithiasis Risk: Drugs that increase nephrolithiasis risk include: 1) Acyclovir (due to crystal formation); 2) Loop diuretics (by increasing urinary calcium excretion, leading to precipitation); and 3) Trimethoprim-sulfamethoxazole (TMP-SMX).
• Primary Hyperaldosteronism (Conn Syndrome): Suspected when a patient presents with resistant hypertension, hypokalemia, and metabolic alkalosis. Diagnosis is strongly suggested by a high plasma aldosterone to renin ratio (PAC/PRA > 30).
• RAS vs FMD: Pathophysiology dictates the difference: Renal Artery Stenosis (RAS) involves atherosclerosis of the intima; Fibromuscular Dysplasia (FMD) affects the vascular media.
• Aldosterone Antagonists: Drugs like Spironolactone and Eplerenone are used for Conn Syndrome. Spironolactone is particularly notable because it also blocks androgen receptors, leading to a risk of gynecomastia.

Learning objectives

• Differentiate the pathophysiology of renal artery stenosis (atherosclerosis) versus fibromuscular dysplasia (media defect).
• Recognize the classic clinical triad and diagnostic lab findings for primary hyperaldosteronism.
• Understand the mechanisms by which various drugs (e.g., acyclovir, loop diuretics) can precipitate nephrolithiasis.
• Apply knowledge of aldosterone receptor antagonists, including their side effects and appropriate use in heart failure.
• Correlate endocrine symptoms (hypokalemia, metabolic alkalosis) with mineralocorticoid excess.

Board exam buzzwords

Rapid review table

Board-speak -> diagnosis

Differential diagnosis / distinguishing features

Gynecomastia Causes

Management pearls

• Conn Syndrome Workup: The diagnostic sequence is: 1) Check PAC/PRA ratio (>30); 2) Perform a Salt Suppression Test (diagnostic confirmation); 3) If unilateral, perform Adrenal Vein Sampling to localize the source.
• Aldosterone Antagonist Use in HF: Do NOT initiate spironolactone or eplerenone for Heart Failure unless the patient has already been on both a Beta Blocker and an ACE inhibitor/ARB, AND their EF is <40%.
• Spironolactone Side Effects: Be aware of its anti-androgenic effects (blocking androgen receptors) which can cause gynecomastia.
• Herpes Zoster Treatment: Initiate acyclovir early to limit viral shedding and prevent complications; monitor for nephrotoxicity.

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Integration & clinical reasoning

• Endocrine/Renal Integration: The triad of resistant hypertension, hypokalemia, and metabolic alkalosis immediately directs suspicion toward mineralocorticoid excess (Conn Syndrome), necessitating a PAC/PRA ratio check.
• Pharmacology/Nephrology Integration: Understanding the mechanism of action for drugs like acyclovir (false nucleotide) is crucial because its toxicity profile (nephrolithiasis risk) must be considered alongside other nephrotoxic agents (e.g., loop diuretics).
• Endocrinology/Gynecology Integration: Gynecomastia can stem from multiple sources—endocrine imbalance (prolactinoma, liver failure), drug side effects (anti-androgens, antipsychotics), or genetic syndromes (Klinefelter's)—requiring a comprehensive history and physical exam.

OMM / COMLEX integration

• Standard emergency management for acute kidney injury or adrenal crisis takes priority over OMT. However, understanding the endocrine axis (RAAS system) and electrolyte imbalances is crucial for comprehensive patient care.
• When managing resistant hypertension, recognizing that aldosterone excess can lead to severe hypokalemia/metabolic alkalosis requires immediate attention to fluid and electrolyte balance before considering advanced interventions.

Concept connections / cross-references

• For detailed information on the pathophysiology of mineralocorticoid excess and its management, review [Episode 37].
• The mechanism of action for anti-psychotic drugs and their effect on dopamine receptors is covered in detail in [Episode 12].

High-yield association table

Key terms glossary

Study optimization

Question pattern recognition

• Resistant HTN + Hypokalemia + Metabolic Alkalosis: Always think of primary hyperaldosteronism (Conn Syndrome). The first test is the PAC/PRA ratio.
• Vesicular rash on erythematous base with sharp borders: Highly suggestive of Herpes Zoster, requiring prompt antiviral therapy and monitoring for nephrotoxicity.
• Gynecomastia in a young male: Consider hormonal imbalances: hyperprolactinemia (drug or tumor), liver failure (estrogen metabolism), or anti-androgenic drugs.

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