Source / episode info

• **Episode:**577
• **Title:**DIP Ep 577: USMLE Step 2/3 Rapid Review Series 119
• **Published:**2025-03-03
• Source:Episode page

One-liner

This episode provides a high-yield rapid review covering Cushing syndrome diagnosis and workup (LDDST, UFC), adrenal crisis management post-adrenalectomy, distinguishing indirect vs. direct inguinal hernias, pre-operative screening for atlantoaxial instability in RA, and the metabolic differences between folate and B12 deficiency related to methotrexate use.

High-yield summary

• Cushing Syndrome: Classic findings include weight gain, hypertension (due to mineralocorticoid effects), hypokalemia, and metabolic alkalosis (due to increased H+ excretion). Diagnosis requires failure of cortisol suppression after low-dose dexamethasone testing (LDDST) and elevated 24-hour urine free cortisol (UFC).
• ACTH Dependence vs. Independence: Skin hyperpigmentation suggests high ACTH production (e.g., Cushing's disease, Adrenalitis), as ACTH is derived from POMC, which also yields Melanocyte Stimulating Hormone (MSH). Lack of hyperpigmentation suggests adrenal source or pituitary failure.
• Adrenal Crisis Post-adrenalectomy: After removing an adenoma causing cortisol excess, the contralateral normal gland may be suppressed by chronic high ACTH/cortisol levels and will require stressed glucocorticoid replacement to prevent acute adrenal insufficiency.
• Inguinal Hernia Anatomy: Indirect inguinal hernias are lateral to the inferior epigastric vessels; direct inguinal hernias are medial to them. Always rely on anatomical landmarks, not just age heuristics.
• RA/Cervical Spine: Patients with RA, Down syndrome, or Ankylosing Spondylitis require screening for atlantoaxial instability (C1-C2 subluxation) via plain cervical X-ray before any neck manipulation.
• Methotrexate Metabolism: Folate deficiency causes elevated homocysteine but normal methylmalonic acid; B12 deficiency causes elevated both homocysteine and methylmalonic acid.

Learning objectives

• Differentiate the biochemical and clinical presentations of primary vs. secondary adrenal insufficiency.
• Interpret Cushing syndrome screening results (LDDST, UFC) to determine ACTH dependence/independence.
• Apply anatomical knowledge to correctly classify inguinal hernias based on relation to inferior epigastric vessels.
• Identify high-risk populations requiring pre-operative cervical spine imaging due to atlantoaxial instability.
• Correlate drug metabolism pathways (e.g., methotrexate) with specific electrolyte and amino acid abnormalities (homocysteine, methylmalonic acid).