Source / episode info

• **Episode:**584
• **Title:**DIP Ep 584: 2025 USMLE Step 1 Free 120 Discussion Part 4 (Q31-40, super helpful for Step 2 and 3!)
• **Published:**2025-03-21
• Source:Episode page

One-liner

This episode covers a broad range of topics including soft tissue sarcomas (Rhabdomyosarcoma), gallstone etiology related to hemolysis, sarcoidosis-induced hypercalcemia via calcitriol excess, common vaginal infections (Candidiasis), neurological deficits like cervical myelopathy and MLF palsy, cardiovascular emergencies (Aortic Dissection), and pulmonary histology/regeneration.

High-yield summary

• Rhabdomyosarcoma: A soft tissue sarcoma characterized by malignant cells with striated appearance; it is the most likely diagnosis for a muscle-based mass in a child presenting with exophthalmus.
• Sarcoidosis Hypercalcemia: Caused by epithelioid macrophages within granulomas overexpressing 1--hydroxylase, leading to excessive production of active Vitamin D (Calcitriol), which drives intestinal calcium absorption and suppresses PTH.
• Alveolar Regeneration: Type II pneumocytes are crucial for lung repair; they differentiate into Type I pneumocytes and produce surfactant.
• Cervical Myelopathy Pattern: Characterized by a mix of signs: lower motor neuron (LMN) signs at high levels (e.g., hand atrophy, weakness) and upper motor neuron (UMN) signs at low levels (e.g., hyperreflexia, Babinski sign). C8-T1 root involvement is classic for intrinsic hand muscle deficits.
• MLF Palsy: Diplopia caused by damage to the Medial Longitudinal Fasciculus (MLF), which coordinates conjugate horizontal gaze; an adduction deficit suggests a lesion in the ipsilateral MLF.

Learning objectives

• Differentiate between various types of gallstones and their underlying metabolic causes.
• Recognize the classic clinical presentation and anatomical level of cervical myelopathy.
• Understand the pathophysiology linking sarcoidosis to hypercalcemia via Vitamin D metabolism dysregulation.
• Identify the primary cell type responsible for alveolar repair in lung injury (Type II pneumocytes).
• Interpret cranial nerve deficits related to conjugate gaze (MLF) and spinal cord levels (C8-T1).

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