Source / episode info

• **Episode:**483
• **Title:**Divine Intervention Episode 483: USMLE Step 2/3 Rapid Review Series 102
• **Published:**2023-09-20
• Source:Episode page

One-liner

This episode provides a rapid review of high-yield infectious diseases (e.g., Leptospirosis, Schistosomiasis, Nocardiosis) and inflammatory conditions (Sarcoidosis, RA), emphasizing the importance of exposure history, specific diagnostic findings, and differential diagnosis traps on board exams.

High-yield summary

• Sarcoidosis: Characterized by non-caseating granulomas and often presents with a triad: bilateral hilar lymphadenopathy, arthritis, and erythema nodosum (Lovegren syndrome). The mechanism of hypercalcemia involves activated macrophages converting 25-OH Vitamin D to active 1--hydroxylase.
• Leptospirosis: A spirochetal infection acquired from animal/rodent urine exposure (e.g., post-flood, plumber). Key signs include fever, myalgia, and conjunctival suffusion; severe disease is called Weil's disease.
• Schistosomiasis: Caused by Schistosoma species, typically associated with contaminated fresh water sources in endemic areas (e.g., Africa/Middle East). Manifestations include hematuria and can lead to liver failure/cirrhosis.
• Environmental Infections: Earth disturbance or trauma suggests Coxiella burnetii (Q fever) or other environmental pathogens; diagnosis often involves interstitial infiltrates and erythema nodosum.
• Acid-Fast Bacilli Traps: When encountering acid-fast positive organisms, always rule out non-tuberculosis mycobacteria (NTM) like Nocardia, which can cause multi-organ involvement (lungs, brain, skin).
• Babesiosis: A bloodborne protozoal infection transmitted by ticks/mosquitoes that targets red blood cell precursors, leading to hemolysis and elevated indirect bilirubin.

Learning objectives

• Differentiate between various tropical/environmental pathogens based on specific exposure history (e.g., water source, animal contact, soil disturbance).
• Recognize the classic clinical and pathological features of Sarcoidosis, including its metabolic consequences (hypercalcemia).
• Understand the key diagnostic clues for spirochetal infections like Leptospirosis and Schistosomiasis.
• Master the differential diagnosis between common acid-fast organisms (e.g., Nocardia vs. TB) and environmental pathogens (Coxiella).
• Correlate clinical findings with specific pathogen mechanisms, such as Babesia's targeting of red blood cell precursors or Schistosoma's ability to cause cirrhosis.