Source / episode info

• **Episode:**125
• **Title:**Divine Intervention Episode 125 – USMLE Step 2CK Rapid Review Series 6 (IM)
• **Published:**2019-07-20
• Source:Episode page

One-liner

This episode provides a rapid review covering high-yield topics including HSV meningoencephalitis and subarachnoid hemorrhage differentials, the classic signs of transtentorial herniation (CN III palsy), tuberculosis diagnosis protocols (PPD cutoffs, INH toxicity), rhabdomyolysis management, and the pathophysiology of Type I through IV hypersensitivity reactions.

High-yield summary

• HSV Encephalitis: Classically presents with temporal lobe involvement, seizures, or focal neurological deficits; CSF findings may show lymphocytic pleocytosis (though red blood cells can be seen in SAH).
• Transtentorial Herniation: Compression of CN III causes a "down and out" eye due to paralysis of the levator palpebrae superioris and inferior rectus. Compression of CN VI/CN V leads to other deficits; compression of CN III also impairs parasympathetic function, leading to mydriasis (blown pupil).
• Tuberculosis (TB): The PPD cutoff values are critical: 15 mm for healthy individuals, 10 mm for healthcare workers, and 5 mm for immunocompromised patients (e.g., HIV/IV drug users). Latent TB is treated with Isoniazid (INH) for nine months plus Vitamin B6 supplementation to prevent peripheral neuropathy.
• Rhabdomyolysis: Characterized by muscle injury leading to myoglobinuria, which can cause acute kidney injury (AKI) and electrolyte abnormalities like hyperkalemia and hypocalcemia. Treatment involves aggressive IV fluid resuscitation.
• Hypersensitivity Reactions: Type I is IgE-mediated (e.g., asthma); Type II is antibody-mediated against fixed antigens (e.g., autoimmune hemolytic anemia); Type III is immune complex deposition (e.g., post-streptococcal glomerulonephritis); and Type IV is delayed T-cell mediated (e.g., contact dermatitis).

Learning objectives

• Differentiate between HSV meningoencephalitis, subarachnoid hemorrhage, and other causes of altered mental status with elevated CSF red blood cells.
• Describe the specific cranial nerve deficits associated with transtentorial herniation (CN III palsy).
• Apply appropriate PPD cutoff values for diagnosing tuberculosis based on patient risk factors.
• Recognize the pathophysiology and acute management steps for rhabdomyolysis, including electrolyte correction.
• Classify and provide clinical examples of Type I through IV hypersensitivity reactions.

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