1. C
The left anterior descending (LAD) artery supplies the anterior wall and septum; ST-elevation in V1–V4 indicates an LAD occlusion.

2. B
Hashimoto thyroiditis is the most common cause of hypothyroidism in iodine-sufficient areas with anti-TPO and anti-thyroglobulin antibodies.

3. C
Squamous cell carcinoma presents as a central mass in smokers and shows keratin pearls and intercellular bridges.

4. B
Streptococcus pneumoniae is the most common cause of bacterial meningitis in adults, with classic CSF findings.

5. B
The MCA is the most common embolic stroke site, supplying face/upper limb motor-sensory areas and language areas.

6. C
Post-streptococcal glomerulonephritis is due to immune complex deposition after a group A strep infection.

7. C
Mixed germ cell tumor is indicated by elevated AFP and β-hCG; seminomas do not elevate AFP.

8. C
Clostridium perfringens produces alpha-toxin causing gas gangrene through tissue fermentation.

9. C
Ammonia → glutamine accumulation in astrocytes causes swelling and cerebral edema in hepatic encephalopathy.

10. C
Prolactinomas are treated first-line with dopamine agonists (cabergoline, bromocriptine).

11. B
X-linked agammaglobulinemia involves BTK mutation preventing B-cell maturation and causing low immunoglobulins.

12. B
Alpha-blockade must precede beta-blockade in pheochromocytoma to avoid hypertensive crisis.

13. B
BPH involves hyperplasia in the transition zone, while prostate cancer usually arises in the peripheral zone.

14. B
Chlamydia trachomatis is the most common cause of PID; cervical motion tenderness is classic.

15. B
Esophageal varices arise from left gastric vein–esophageal vein anastomosis due to portal hypertension.

16. B
Myasthenia gravis is due to autoantibodies against nicotinic ACh receptors, causing fatigable weakness.

17. C
Malignant otitis externa is a Pseudomonas infection in diabetics/immunocompromised patients causing skull-base osteomyelitis.

18. B
Meniere disease is due to endolymphatic hydrops; presents with vertigo, sensorineural loss, tinnitus, and fullness.

19. B
CA 19-9 is the main tumor marker for pancreatic adenocarcinoma; Courvoisier sign indicates malignancy.

20. A
Wilms tumor involves WT1/WT2 gene deletions and shows triphasic histology in young children.

21. B
Achalasia is caused by loss of inhibitory neurons (VIP, NO) in the myenteric plexus leading to LES dysfunction.

22. B
Calcium oxalate stones show octahedral crystals; management includes hydration, citrate, and dietary modification.

23. C
Diffuse proliferative lupus nephritis (class IV) shows wire-loop lesions and affects >50% of glomeruli.

24. C
Glucagonoma shows necrolytic migratory erythema, diabetes, DVT, and depression.

25. C
Viridans streptococci cause subacute bacterial endocarditis and are alpha-hemolytic, optochin-resistant.

26. B
Anti-CCP antibodies are highly specific for rheumatoid arthritis and predict erosive disease.

27. B
Multiple myeloma causes lytic bone lesions via osteoclast activation from cytokines like IL-1, IL-6, and RANKL.