Source / episode info

• **Episode:**261
• **Title:**Divine Intervention Episode 261 – USMLE Dermatology 3 (Part 3 of 3) + Reminder of 2CK Courses from 9/21-23.
• **Published:**2020-09-17
• Source:Episode page

One-liner

This episode provides a comprehensive review of dermatologic associations, covering drug allergy cross-reactivity (penicillins), photosensitivity syndromes (S.A.T.), bullous autoimmune diseases (Pemphigus/Bullous Pemphigoid), and systemic manifestations like pyoderma gangrenosum, amyloidosis, and lupus pernio.

High-yield summary

• Penicillin Allergy: Skin testing is preferred over RAST/ELISA. An unallergic reaction to penicillin mandates avoiding all penems (e.g., carbapenems) AND cephalosporins due to potential cross-reactivity.
• Photosensitivity Triad (S.A.T.): Sulfonamides (SMX), Aminodarone, and Tetracyclines are classic causes of photosensitivity.
• Bullous Autoimmunity: Pemphigus Vulgaris (PV) shows intercellular IgG deposition on DIF with a positive Nikolsky sign; Bullous Pemphigoid (BP) shows linear IgG deposition in the basement membrane with negative Nikolsky sign.
• Systemic Associations: Pyoderma Gangrenosum (PG) is strongly associated with Inflammatory Bowel Disease (IBD). Nephrogenic Systemic Fibrosis (NSF) is caused by Gadolinium exposure, especially in patients with Chronic Kidney Disease (CKD).
• Drug Reactions/Infections: Jarisch-Herxheimer reaction occurs hours after starting antibiotics for spirochetal infections due to endotoxin release; supportive care is given, and antibiotics must not be stopped.

Learning objectives

• Differentiate the clinical and immunofluorescent findings between Pemphigus Vulgaris and Bullous Pemphigoid.
• Identify classic associations between systemic diseases (e.g., IBD, CKD) and specific dermatological manifestations (PG, NSF).
• Recall the mnemonic and associated drugs for photosensitivity reactions (S.A.T.).
• Recognize the signs and management of acute infectious reactions like Jarisch-Herxheimer syndrome.
• Understand the differential diagnosis and initial workup for bullous rashes (e.g., PV vs BP vs SJS/TEN).

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