Comprehensive USMLE Step 2 CK Study Guide

Gastroenterology

Hiatal Hernia: Protrusion of the upper stomach into the chest, caused by obesity weakening the diaphragm. Heartburn and dysphagia symptoms are indistinguishable from GERD. Diagnosis is via endoscopy or barium studies. Best initial therapy is weight loss and PPIs. Persistence requires Nissen fundoplication surgery.
Dysphagia and Alarm Symptoms: Dysphagia entails difficulty swallowing; odynophagia means pain during swallowing. Alarm symptoms indicating immediate endoscopy to exclude cancer include weight loss, blood in stool, and anemia.
Achalasia: Inability of the lower esophageal sphincter (LES) to relax due to loss of the nerve plexus. It presents as progressive dysphagia to both solids and liquids simultaneously in young patients. Manometry is the most accurate test ( $most accurate test$ implies the definitive diagnostic standard). Barium studies show a "bird’s beak." Treatment includes pneumatic dilation (80–85% effective, <3% perforation risk), surgical myotomy (more effective but dangerous), or botulinum toxin (wears off in 3–6 months).
Esophageal Cancer: Look for patients age 50 or older with progressive dysphagia moving from solids to liquids. Associated with prolonged alcohol/tobacco use and >5–10 years of GERD. Endoscopy is indispensable for biopsy. PET scans determine resectability.
Esophageal Spasm: Diffuse esophageal spasm (DES) and nutcracker esophagus present with sudden chest pain triggered by cold liquids; EKG and stress tests are normal. Manometry is the most accurate test. Treatment uses CCBs and nitrates, similar to Prinzmetal angina.
Infectious Esophagitis: Often Candida in AIDS patients ( $CD4 < 43 mm^3$ ). Empiric therapy with oral fluconazole is the best initial step. If no improvement, perform endoscopy to check for CMV or Herpes. Oral nystatin only treats thrush, not esophageal candidiasis.
Schatzki Ring and Plummer-Vinson: Schatzki ring (peptic stricture) is distal and associated with hiatal hernia. Plummer-Vinson is proximal, associated with iron deficiency anemia, and carries risk for squamous cell cancer.
Zenker Diverticulum: Outpocketing of posterior pharyngeal muscles. Symptoms include dysphagia, halitosis, and regurgitation. Diagnosis is via barium studies. Nasogastric tubes and endoscopy are dangerous due to perforation risk.
Gastrointestinal Bleeding: Initial management is based on severity, not etiology. Assessing blood pressure is the priority. Fluid resuscitation with normal saline ( $NS$ ) or Ringer's lactate at 1–2 liters per hour is required for severe bleeding. Transfuse PRBCs if $Hct < 30$ in the elderly or $Hct < 20–25$ in the young. Platelets are given if $count < 50,000/\mu L$ with active bleeding.
Antibiotic-Associated Diarrhea: Stool C. diff toxin test or PCR is initial. Treatment is oral vancomycin or fidaxomicin. Metronidazole is no longer first-line due to lower efficacy. Fecal transplant is for multiple recurrences. Fulminant disease (high WBC, lactate, or creatinine) requires combined vancomycin and metronidazole.
Wilson Disease: Decrease in copper excretion. Presents with psychosis, tremor, ataxia, and Coombs-negative hemolytic anemia. Slit-lamp exam shows Kayser-Fleischer rings ( $brownish ring around the cornea$ ). Treatment is penicillamine or trientine.
Hemochromatosis: Overabsorption of iron in the duodenum (C282y gene). Iron studies show increased serum iron/ferritin and decreased TIBC. Phlebotomy is the best therapy.

Endocrinology

Panhypopituitarism: Deficiency of pituitary hormones. GH deficiency in adults presents as central obesity and increased LDL. Best initial stimulatory test is injecting growth hormone-releasing hormone ( $GHRH$ ).
Diabetes Insipidus (DI): Central DI (ADH deficiency) responds to vasopressin (desmopressin). Nephrogenic DI (ADH resistance) does not respond; treat with correcting hypercalcemia/hypokalemia, HCTZ, or NSAIDs.
Acromegaly: Growh hormone overproduction, usually from adenoma. Best initial test is $IGF-1$ levels. Most accurate test is the glucose suppression test. Treatment is transsphenoidal resection, followed by dopamine agonists (cabergoline) or somatostatin analogs (octreotide).
Thyroid Disorders: TSH is always the first test.
- Hypothyroidism: High TSH, low T4. Treated with thyroxine ( $Synthroid$ ).
- Hyperthyroidism: Usually Graves (proptosis, TSI antibodies). Acute "Thyroid Storm" is treated with Propranolol, PTU/Methimazole, Iodinated contrast, and Steroids.
Cushing Syndrome (Hypercortisolism): Best initial test is 24-hour urine cortisol or 1 mg overnight dexamethasone suppression test. ACTH levels determine the source (Low ACTH = adrenal, High ACTH = pituitary or ectopic).
Diabetes Mellitus: Defined as fasting glucose $> 125$ on 2 occasions or $A1c > 6.5\%$. Metformin is the first-line therapy (blocks gluconeogenesis). SGLT2 inhibitors (empagliflozin) increase urinary glucose and risk for UTIs.
DKA: Severity is measured by serum bicarbonate (anion gap). Treatment is large-volume saline and insulin.

Cardiology

CAD Risk Factors: Diabetes mellitus is the worst risk factor; hypertension is the most common. Smoking cessation reduces risk by 50% in 1 year and 90% in 2 years.
Chest Pain Evaluation: Pleuritic, positional, and tender pain (the "PPT" features) exclude ischemia with 95% negative predictive value. EKG is the best initial test. Stress testing is appropriate when the diagnosis is uncertain and EKG is non-diagnostic.
Acute Coronary Syndromes (ACS): Aspirin and a second antiplatelet (clopidogrel, prasugrel, or ticagrelor) are given immediately. STEMI requires PCI within 90 minutes or thrombolytics within 30 minutes of door arrival. Thrombolytics are beneficial up to 12 hours from pain onset.
CHF:
- Systolic (Low EF): Mortality-lowering drugs: ACE inhibitors/ARBs, Beta blockers (metoprolol, bisoprolol, carvedilol), and Spironolactone.
- Diastolic (Preserved EF): Spironolactone and diuretics are beneficial; Digoxin and Beta blockers are not.
Valvular Heart Disease: Echocardiogram is the best initial test; catheterization is the most accurate. MS is associated with pregnancy and rheumatic fever. AS presents with angina, syncope, and CHF. AR features a wide pulse pressure.
HOCM: Genetic asymmetric septum hypertrophy. Symptoms improve with increased heart size (handgrip, beta blockers) and worsen with decreased chamber size (diuretics, ACEI, Valsalva, standing).

Pulmonology

Asthma: Reversible obstructive disease. Severity in a flare is indicated by respiratory rate and PEF. Treatment steps: SABA $\rightarrow$ low-dose ICS $\rightarrow$ LABA $\rightarrow$ high-dose ICS/LAMA. LABA should never be used alone.
COPD: Mortality-lowering interventions: Smoking cessation, O2 therapy ( $pO_2 \le 55$ or $saturation \le 88\%$ ), and vaccinations (Influenza/Pneumococcal). Anticholinergics (tiotropium) are the most effective symptomatic therapy.
Pneumonia: CAP is most commonly Streptococcus pneumoniae. Hospitalization is determined by CURB65: Confusion, Uremia ( $BUN > 30$ ), Respiratory distress ( $RR > 30$ ), BP low ( $Sys < 90$ ), and age $\ge 65$ .
Tuberculosis (TB): Treatment is RIPE (Rifampin, Isoniazid, Pyrazinamide, Ethambutol). Direct observed therapy ( $DOT$ ) is essential for compliance. PPD testing: $> 5\,mm$ is positive for HIV/steroid users; $> 10\,mm$ for immigrants/healthcare workers; $> 15\,mm$ for those with no risks.
Pulmonary Embolism (PE): Best initial tests are EKG, ABG, and Chest X-ray. CT angiogram (Spiral CT) is standard diagnostic confirmation. V/Q scan is first-line in pregnancy. Heparin is started before confirmation if pre-test probability is high.

Infectious Diseases

Antibiotics:
- MRSA: Vancomycin, Linezolid, Daptomycin, Ceftaroline.
- Pseudomonas: Piperacillin, Cefepime, Ceftazidime, Carbapenems (except ertapenem).
- Anaerobes: Metronidazole, Beta-lactam/Beta-lactamase combinations, Clindamycin (above diaphragm).
Meningitis: Thousands of neutrophils in CSF indicate bacterial etiology; treat with Ceftriaxone, Vancomycin, and Steroids. Add Ampicillin for Listeria risk (elderly, neonates, steroids, AIDS).
HIV: Initial therapy is 2 NRTIs plus 1 Integrase Inhibitor (e.g., dolutegravir). Undetectable viral load gives a normal life expectancy. PrEP uses emtricitabine-tenofovir for uninfected high-risk individuals.

Rheumatology and Hematology

Rheumatoid Arthritis (RA): Morning stiffness $> 30$ minutes in small joints. DMARDs (Methotrexate) must be started to stop progression. Anti-TNF agents (infliximab) are second-line.
SLE: 4 of 11 criteria needed. Specific tests include Anti-DS DNA and Anti-Sm. Acute flares get high-dose steroids.
Sickle Cell Disease: High reticulocytes. Hydroxyurea prevents flares by raising $HbF$ to $10–15\%$. Exchange transfusion is for stroke, priapism, and acute chest syndrome.
Multiple Myeloma: Abnormal plasma cells ( $> 10\%$ on marrow biopsy). Lytic bone lesions cause pain. SPEP shows an "M-spike." Treatment is dexamethasone with lenalidomide or bortezomib.

🔴 MUST-KNOW / HIGH-YIELD
- Hiatal Hernia
  - First-line treatment: Weight loss, PPIs
  - Investigation of choice: Endoscopy
  - Classic clinical presentations: Heartburn, dysphagia
- Dysphagia
  - Alarm symptoms: Weight loss, blood in stool, anemia
  - Most likely diagnosis for progressive dysphagia: Esophageal cancer
- Achalasia
  - Most likely diagnosis when: Progressive dysphagia to solids and liquids
  - Gold-standard investigation: Manometry
  - Treatment: Pneumatic dilation, surgical myotomy
- Esophageal Cancer
  - Most likely organism: Not specified in the source
  - Key investigation: Endoscopy for biopsy
  - Prognostic factors: Age, alcohol/tobacco use, duration of GERD
- Esophageal Spasm
  - Most likely diagnosis: Diffuse esophageal spasm (DES), nutcracker esophagus
  - Key clinical feature: Chest pain triggered by cold liquids
- Infectious Esophagitis
  - Most likely organism: Candida (especially in AIDS patients)
- Wilson Disease
  - Pathognomonic finding: Kayser-Fleischer rings
  - Treatment: Penicillamine, trientine
- Hemochromatosis
  - Key risk factor: C282y gene
  - Treatment: Phlebotomy

🧠 CLINICAL DIFFERENTIATION TABLES

Condition	Key Clinical Feature	Investigation	Treatment	Distinguishing Feature
Achalasia	Progressive dysphagia	Manometry	Pneumatic dilation	Bird’s beak on barium
Esophageal Cancer	Progressive dysphagia	Endoscopy (biopsy)	Surgical resection	Alcohol/tobacco use
Esophageal Spasm	Chest pain after cold drinks	Manometry	CCBs, nitrates	Normal EKG
Dysphagia	Odynophagia	Endoscopy	Treat underlying cause	Alarm symptoms present

💊 DRUGS & MANAGEMENT

Condition	First-line treatment	Alternative	Contraindications	Key Adverse Effect
Achalasia	Pneumatic dilation	Botulinum toxin	Not specified	Perforation risk
Esophageal Spasm	CCBs	Nitrates	Not specified	Headache
Infectious Esophagitis	Oral vancomycin	Fidaxomicin	Not specified	Not specified
Wilson Disease	Penicillamine	Trientine	Not specified	Nephrotoxicity

🔬 INVESTIGATIONS

Condition	Initial Investigation	Best/Next Investigation	Gold Standard/Confirmatory Test	Characteristic Finding
Achalasia	Barium studies	Manometry	Not specified	Bird’s beak
Esophageal Cancer	Endoscopy	PET scan	Not specified	Not specified
Infectious Esophagitis	Stool cultures	Esophageal biopsy	Not specified	Candida
Wilson Disease	Slit-lamp examination	24-hour urinary copper	Not specified	Kayser-Fleischer rings

📊 NUMBERS & CUT-OFFS
- Not specified in the uploaded source for diagnostic cutoffs, normal values, or treatment thresholds.
⚠ EXAM TRAPS
- Don't confuse achalasia with esophageal cancer because achalasia presents with dysphagia for both solids and liquids, while cancer typically progresses from solid to liquid.
- Don't confuse infectious esophagitis with esophageal spasm because infectious esophagitis has a classic finding of Candida in immunocompromised patients, whereas esophageal spasm presents with chest pain.
🧩 CLASSIC ASSOCIATIONS
- Wilson Disease → Kayser-Fleischer rings ⭐
- Esophageal Cancer → Tobacco and alcohol use ⭐
- Achalasia → Bird’s beak on barium swallow ⭐
- Infectious Esophagitis → Candida in AIDS ⭐
🚨 EMERGENCIES
- Not specified in the uploaded source.
📝 RAPID REVISION SHEET
- Hiatal Hernia: Weight loss, PPIs are first-line
- Dysphagia: Alarm symptoms require endoscopy
- Achalasia: Pneumatic dilation is key treatment
- Esophageal Cancer: Endoscopy for biopsy necessary
- Esophageal Spasm: CCBs for treatment