Internal Medicine

Internal Medicine for Clinical Rotations

Master internal medicine essentials with free flashcards and spaced repetition practice to prepare for clinical rotations and Step 2 CK. This comprehensive lesson covers diagnostic reasoning, common disease presentations, evidence-based management strategies, and clinical pearls—all critical for success in your internal medicine clerkship and board examinations.

Welcome to Internal Medicine 🏥

Internal medicine forms the foundation of clinical practice, encompassing the prevention, diagnosis, and treatment of adult diseases. During your IM rotation, you'll encounter a vast spectrum of pathology—from acute presentations like chest pain and dyspnea to chronic conditions like diabetes and heart failure. This lesson focuses on high-yield concepts, systematic approaches to common clinical scenarios, and practical management pearls that will serve you throughout your career.

Why Internal Medicine Matters:

• 📊 Most frequently tested specialty on Step 2 CK
• 🎯 Foundation for all other specialties
• 🔍 Develops critical diagnostic reasoning skills
• 💊 Emphasizes evidence-based treatment decisions

Core Concepts in Internal Medicine

🫀 Cardiovascular Medicine

Chest Pain Evaluation

The approach to chest pain requires systematic risk stratification. Remember the life-threatening causes with the mnemonic "TAPUM":

• Tension pneumothorax
• Acute coronary syndrome (ACS)
• Pulmonary embolism
• Ulcer (perforated)
• Mediastinal rupture (aortic dissection, esophageal rupture)

Acute Coronary Syndrome (ACS) Management:

Presentation	ECG Findings	Initial Treatment
STEMI	ST elevation ≥1mm in 2+ contiguous leads	Reperfusion (PCI or fibrinolysis) within 90-120 min
NSTEMI	ST depression, T-wave inversion, or normal	Antiplatelet, anticoagulation, risk stratification
Unstable Angina	ST depression, T-wave changes, or normal	Same as NSTEMI; troponins negative

💡 Clinical Pearl: All ACS patients receive "MONA BASH" therapy:

• Morphine (if pain persists)
• Oxygen (if SpO2 <90%)
• Nitroglycerin
• Aspirin (162-325 mg chewed)
• Beta-blocker (within 24h if no contraindications)
• ACE inhibitor (especially if anterior MI or EF <40%)
• Statin (high-intensity)
• Heparin (anticoagulation)

Heart Failure Classification:

HEART FAILURE TYPES

┌─────────────────────────────────────────────────┐
│                                                 │
│  HFrEF (Reduced EF <40%)    HFpEF (Preserved)  │
│         │                          │            │
│         ↓                          ↓            │
│  Systolic dysfunction      Diastolic problem    │
│  Dilated ventricle         Stiff ventricle      │
│  ↓ Contractility           ↓ Relaxation         │
│         │                          │            │
│         ↓                          ↓            │
│  β-blockers, ACEi          Treat HTN, control   │
│  Diuretics, Spironolactone rate in AFib         │
│                                                 │
└─────────────────────────────────────────────────┘

⚠️ Common Mistake: Don't confuse HFrEF and HFpEF treatment! Beta-blockers, ACE inhibitors, and spironolactone have mortality benefit ONLY in HFrEF. HFpEF management focuses on symptom control and treating underlying conditions.

🫁 Pulmonary Medicine

Dyspnea Differential Approach

Systematic evaluation prevents missed diagnoses:

DYSPNEA DECISION TREE

        Acute Dyspnea
              │
    ┌─────────┴─────────┐
    │                   │
 Hypoxic           Normal O₂
    │                   │
    ↓                   ↓
┌───────────┐    ┌──────────────┐
│Cardiac vs │    │Hyperventilation│
│Pulmonary  │    │Anxiety        │
│Cause      │    │Metabolic      │
└─────┬─────┘    └──────────────┘
      │
  ┌───┴────┐
  ↓        ↓
 Cardiac  Pulmonary
  │        │
  ↓        ↓
• PE      • Pneumonia
• MI      • Pneumothorax
• CHF     • Asthma/COPD
          • Aspiration

Pulmonary Embolism (PE) Workup:

Step 1: Calculate Wells Score or use PERC rule

• Low probability + PERC negative → No further workup
• Low probability + PERC positive → D-dimer
• Moderate/High probability → Skip D-dimer, go to imaging

Step 2: D-dimer (high sensitivity, low specificity)

• Negative → Rules out PE in low-probability patients
• Positive → Proceed to CT angiography

Step 3: CT pulmonary angiography (CTPA) = gold standard

💡 Clinical Pearl: D-dimer is only useful when negative in low-risk patients. It's elevated in many conditions (pregnancy, cancer, surgery, infection), so a positive result doesn't confirm PE.

COPD Exacerbation Management:

Severity	Treatment	Key Points
Mild-Moderate	• Bronchodilators (albuterol, ipratropium) • Steroids (prednisone 40mg × 5 days) • Antibiotics if purulent sputum	Most can be managed outpatient
Severe	• Above treatments • Supplemental O₂ (target 88-92%) • Consider NIV if hypercapnic	⚠️ Avoid high-flow O₂ (may worsen CO₂ retention)
Life-threatening	• Intubation if NIV fails • ICU admission	pH <7.25, altered mental status, exhaustion

🩺 Gastroenterology

Acute Abdominal Pain Localization

┌─────────────────────────────────────────┐
│     ABDOMINAL PAIN LOCALIZATION         │
├─────────────────────────────────────────┤
│                                         │
│  RUQ           Epigastric         LUQ  │
│  • Cholecystitis • PUD          • Splenic│
│  • Hepatitis    • Pancreatitis    rupture│
│  • RLL pneumonia • MI (referred)  • LLL  │
│                 • AAA              pneumo│
│─────────────────────────────────────────│
│  Periumbilical                          │
│  • Early appendicitis                   │
│  • Small bowel obstruction              │
│  • Mesenteric ischemia                  │
│  • AAA                                  │
│─────────────────────────────────────────│
│  RLQ           Suprapubic         LLQ   │
│  • Appendicitis • Cystitis     • Divertic│
│  • Ectopic      • Urinary        ulitis │
│  • Ovarian torsion retention   • Ectopic│
│                • PID           • Ovarian│
│                                  torsion│
└─────────────────────────────────────────┘

Acute Pancreatitis Management:

Diagnosis: Requires 2 of 3 criteria:

1. Abdominal pain (epigastric, radiating to back)
2. Lipase/amylase >3× upper limit of normal
3. Imaging (CT/MRI/ultrasound) showing pancreatitis

Severity Assessment - Ranson Criteria:

At admission:

• Age >55 years
• WBC >16,000
• Glucose >200
• LDH >350
• AST >250

At 48 hours:

• Hct drop >10%
• BUN rise >5
• Ca²⁺ <8
• PaO₂ <60
• Base deficit >4
• Fluid sequestration >6L

💡 Management Essentials:

• Aggressive IV fluids (250-500 mL/hr) - most important intervention!
• NPO initially, advance diet as tolerated (no need to wait for lipase normalization)
• Pain control (morphine is safe despite old dogma)
• Identify cause (gallstones vs alcohol) and treat underlying condition

⚠️ Common Mistake: Don't delay feeding too long! Early enteral nutrition (within 24-48h) is associated with better outcomes. Oral diet can be started when pain improves and patient is hungry.

Cirrhosis Complications - The "Big 5":

Complication	Presentation	Management
Ascites	Abdominal distension, shifting dullness	Na restriction, diuretics (spironolactone + furosemide 100:40 ratio), therapeutic paracentesis if tense
Spontaneous Bacterial Peritonitis	Fever, abdominal pain, altered mental status	Diagnostic paracentesis (PMN >250), 3rd gen cephalosporin + albumin
Hepatic Encephalopathy	Confusion, asterixis, elevated ammonia	Lactulose (target 2-3 soft stools/day), rifaximin
Variceal Bleeding	Hematemesis, melena, hemodynamic instability	Octreotide, antibiotics (ceftriaxone), urgent EGD with banding, consider TIPS if refractory
Hepatorenal Syndrome	Rising Cr without other cause, oliguria	Albumin + midodrine + octreotide, or albumin + norepinephrine; liver transplant definitive

🩸 Hematology/Oncology

Anemia Workup Algorithm:

ANEMIA EVALUATION

    Low Hemoglobin
         │
         ↓
    Check MCV
         │
    ┌────┼────┐
    ↓    ↓    ↓
  <80  80-100 >100
  Micro Normal Macro
    │    │     │
    ↓    ↓     ↓

Type	MCV	Common Causes	Key Tests
Microcytic	<80	• Iron deficiency • Thalassemia • Anemia of chronic disease • Lead poisoning	Iron studies, ferritin, hemoglobin electrophoresis
Normocytic	80-100	• Acute blood loss • Hemolysis • Chronic disease • Chronic kidney disease	Reticulocyte count, hemolysis labs, renal function
Macrocytic	>100	• B12/folate deficiency • Alcohol • Medications (MTX, AZT) • Myelodysplastic syndrome	B12, folate, TSH, peripheral smear

Iron Studies Interpretation:

Condition	Ferritin	TIBC	Serum Iron	Transferrin Sat
Iron Deficiency	↓ <30	↑	↓	↓ <15%
Anemia of Chronic Disease	↑ or Normal	↓	↓	↓
Hemochromatosis	↑↑ >1000	↓	↑	↑ >45%
Thalassemia	Normal/↑	Normal	Normal/↑	Normal

💡 Clinical Pearl: Ferritin is an acute phase reactant. In inflammatory states, it may be falsely elevated, masking concurrent iron deficiency. If ferritin is 30-100 with inflammation, consider trial of iron supplementation.

🔬 Endocrinology

Diabetes Management Goals:

Parameter	Target (Most Patients)	Less Stringent Target
HbA1c	<7%	<8% (elderly, limited life expectancy, severe hypoglycemia history)
Fasting glucose	80-130 mg/dL	<150 mg/dL
Postprandial glucose	<180 mg/dL	<200 mg/dL
Blood pressure	<130/80	<140/90
LDL cholesterol	<100 (or <70 if CAD)	<100

Type 2 Diabetes Medication Selection:

T2DM TREATMENT ALGORITHM

    Metformin (1st line)
          │
          ↓
    If A1c not at goal after 3 months
          │
    ┌─────┴─────┐
    ↓           ↓
 ASCVD or     CKD/HF present?
 high CV risk?    │
    │            ↓
    ↓         Add SGLT2i
 Add GLP-1 RA  (empagliflozin,
(semaglutide,  dapagliflozin)
 liraglutide)
    │
    ↓
If still not at goal,
add basal insulin

Medication Classes - Key Points:

1. Metformin: First-line, weight neutral, ↓ A1c 1-2%, GI side effects, hold if eGFR <30
2. SGLT2 inhibitors: CV and renal benefits, ↓ A1c 0.5-1%, risk of DKA and UTIs, weight loss
3. GLP-1 agonists: CV benefits, ↓ A1c 1-1.5%, weight loss, GI side effects, injectable
4. DPP-4 inhibitors: Moderate efficacy, weight neutral, well-tolerated, expensive
5. Sulfonylureas: Inexpensive but risk of hypoglycemia and weight gain
6. Insulin: Most effective, no dose limit, requires monitoring

Thyroid Disorder Recognition:

Condition	TSH	Free T4	Clinical Features
Primary Hypothyroidism	↑	↓	Fatigue, weight gain, constipation, cold intolerance, bradycardia
Subclinical Hypothyroidism	↑	Normal	Often asymptomatic; treat if TSH >10 or symptomatic
Primary Hyperthyroidism	↓	↑	Weight loss, tremor, palpitations, heat intolerance, diarrhea
Subclinical Hyperthyroidism	↓	Normal	May increase AFib and osteoporosis risk
Secondary Hypothyroidism	Low/Normal	↓	Pituitary dysfunction; check other pituitary hormones

🧠 Nephrology

Acute Kidney Injury (AKI) Classification:

KDIGO Criteria (Stage 1-3):

• Stage 1: Cr ↑ by 0.3 mg/dL within 48h OR ↑ to 1.5-1.9× baseline OR urine output <0.5 mL/kg/h × 6-12h
• Stage 2: Cr ↑ to 2.0-2.9× baseline OR urine output <0.5 mL/kg/h × ≥12h
• Stage 3: Cr ↑ to 3× baseline OR Cr ≥4.0 OR initiation of RRT OR urine output <0.3 mL/kg/h × ≥24h

AKI Etiology - Prerenal vs Intrinsic vs Postrenal:

Type	Causes	FeNa	BUN:Cr Ratio	Urine sediment
Prerenal	Hypovolemia, hypotension, heart failure, renal artery stenosis	<1%	>20:1	Bland, hyaline casts
Intrinsic	ATN (ischemic/toxic), AIN, glomerulonephritis	>2%	<15:1	Muddy brown casts (ATN), WBC casts (AIN), RBC casts (GN)
Postrenal	BPH, stones, malignancy, neurogenic bladder	Variable	Variable	Variable

💡 Clinical Pearl: FeNa = (UNa × PCr)/(PNa × UCr) × 100. Remember: FeNa <1% suggests prerenal (kidneys avidly retaining sodium), but can be falsely low with diuretics. Use FeUrea (<35% = prerenal) if patient on diuretics.

⚠️ Common Mistake: Don't forget to check bladder scan or place Foley catheter to rule out obstruction (postrenal) before extensive workup. It's the easiest cause to identify and treat!

Chronic Kidney Disease (CKD) Management:

Key Interventions by GFR Stage:

Stage	GFR	Actions
1-2	≥60	• Diagnose/treat underlying cause • CV risk reduction • BP control (<130/80) • ACEi/ARB if proteinuria
3a-3b	30-59	• Above measures • Avoid nephrotoxins • Monitor CKD-MBD (PTH, Ca, PO4, vit D)
4	15-29	• Prepare for RRT • Refer to nephrology • Manage anemia (consider ESA if Hgb <10) • Dietary protein restriction
5	<15	• Initiate dialysis or plan transplant • Manage uremic symptoms

🦠 Infectious Disease

Pneumonia Management - CAP vs HAP:

Community-Acquired Pneumonia (CAP):

Outpatient:

• Healthy, no recent antibiotics: Amoxicillin OR doxycycline OR macrolide
• Comorbidities: Amoxicillin-clavulanate + macrolide OR respiratory fluoroquinolone

Inpatient (non-ICU):

• β-lactam (ceftriaxone or ampicillin-sulbactam) + macrolide
• OR Respiratory fluoroquinolone (levofloxacin, moxifloxacin)

ICU:

• β-lactam + azithromycin OR β-lactam + respiratory fluoroquinolone
• Add vancomycin or linezolid if MRSA risk factors
• Add antipseudomonal coverage if risk factors present

💡 CURB-65 Score (predicts mortality, guides admission decision):

• Confusion
• Urea >19 mg/dL (BUN >20)
• Respiratory rate ≥30
• BP: Systolic <90 or diastolic ≤60
• Age ≥65

Score 0-1: Outpatient | Score 2: Inpatient | Score ≥3: Consider ICU

Urinary Tract Infection Management:

Type	First-line Treatment	Duration
Uncomplicated Cystitis (women)	Nitrofurantoin OR TMP-SMX (if local resistance <20%)	5 days (nitrofurantoin) 3 days (TMP-SMX)
Complicated UTI	Fluoroquinolone (ciprofloxacin, levofloxacin)	7-14 days
Pyelonephritis (outpatient)	Fluoroquinolone OR ceftriaxone 1g IV × 1 dose then oral	7 days (FQ) 10-14 days (oral β-lactam)
Pyelonephritis (inpatient)	Fluoroquinolone OR ceftriaxone OR amp-gent (if enterococcus)	14 days total

⚠️ Common Mistake: Don't treat asymptomatic bacteriuria except in pregnancy or before urologic procedures. Treatment increases antibiotic resistance without benefit.

Clinical Examples

Example 1: Chest Pain Evaluation 🫀

Case: A 58-year-old man with hypertension and smoking history presents with 2 hours of substernal chest pressure radiating to the left arm, associated with diaphoresis and nausea.

Approach:

1. Immediate: ECG within 10 minutes, IV access, continuous monitoring
2. MONA: Aspirin 325mg chewed, sublingual nitroglycerin, oxygen if SpO2 <90%
3. ECG shows: 3mm ST elevation in V2-V4 (anterior STEMI)
4. Management:
   • Activate cath lab (door-to-balloon time goal <90 minutes)
   • Dual antiplatelet: Aspirin + P2Y12 inhibitor (ticagrelor or prasugrel)
   • Anticoagulation: Heparin bolus + infusion
   • β-blocker (if no contraindications)
   • High-intensity statin
5. Post-PCI: Continue DAPT × 12 months minimum, cardiac rehab, lifestyle modification

Key Takeaway: Time is muscle! Early recognition and rapid reperfusion save lives and preserve cardiac function.

Example 2: Acute Kidney Injury Workup 🧪

Case: A 72-year-old woman admitted for pneumonia develops oliguria on hospital day 3. Baseline Cr 1.0 → now 2.8 mg/dL.

Systematic Approach:

Step 1: Review medications - Started on ibuprofen for fever, received IV contrast 2 days ago

Step 2: Volume status assessment - Dry mucous membranes, poor skin turgor, low urine output

Step 3: Bladder scan - 50 mL (rules out obstruction)

Step 4: Urinalysis - Specific gravity 1.030 (concentrated), trace protein, no cells/casts

Step 5: Calculate FeNa = 0.4% (suggests prerenal)

Step 6: Labs - BUN 70, Cr 2.8 (BUN:Cr = 25:1, supports prerenal)

Diagnosis: Prerenal AKI (hypovolemia exacerbated by NSAIDs)

Management:

• Stop NSAIDs
• IV fluid resuscitation (isotonic saline)
• Hold ACE inhibitor temporarily
• Monitor Cr daily
• Avoid nephrotoxins

Outcome: Cr returns to 1.2 after 48 hours of hydration

Key Takeaway: Most AKI is prerenal and reversible with early recognition and appropriate volume resuscitation. Always review medication list!

Example 3: Diabetic Ketoacidosis (DKA) 💉

Case: A 24-year-old woman with type 1 diabetes presents with nausea, vomiting, and abdominal pain for 1 day. Ran out of insulin 3 days ago.

Initial Labs:

• Glucose: 520 mg/dL
• pH: 7.18
• HCO3: 10 mEq/L
• Anion gap: 26
• β-hydroxybutyrate: elevated
• K: 4.8 mEq/L

DKA Criteria Met: Glucose >250, pH <7.3, HCO3 <18, anion gap >10

Management Protocol:

Component	Initial Management	Monitoring
Fluids	1L NS bolus, then 250-500 mL/h (total 4-6L in first 24h)	Urine output, vitals
Insulin	0.1 units/kg/h regular insulin IV (NO bolus in DKA)	Glucose q1h (target ↓ 50-75 mg/dL/h)
Potassium	Start K+ replacement when <5.2 (20-40 mEq/L in fluids)	K+ q2-4h (maintain 4-5)
Dextrose	Add D5W when glucose <250 (keep insulin running!)	Continue until anion gap closes

Resolution Criteria:

• Glucose <200 mg/dL
• Anion gap <12
• pH >7.3
• HCO3 >18

⚠️ Critical Point: Don't stop insulin when glucose normalizes! Continue insulin infusion with dextrose-containing fluids until anion gap closes and patient can eat. Premature insulin cessation causes rebound ketoacidosis.

Transition to Subcutaneous Insulin:

• Give long-acting (basal) insulin 2-4 hours before stopping IV insulin
• Overlap prevents gap in coverage
• Calculate total daily dose based on IV insulin requirement

Key Takeaway: DKA management is about correcting four things simultaneously: volume deficit, insulin deficiency, electrolyte abnormalities, and acidosis. The anion gap, not glucose, tells you when ketoacidosis has resolved.

Example 4: Upper GI Bleeding Management 🩸

Case: A 65-year-old man with cirrhosis presents with hematemesis and melena. HR 110, BP 95/60, pale.

Immediate Actions (within 1 hour):

1. Resuscitation:

   • 2 large-bore IVs
   • Transfuse PRBCs (target Hgb 7-9 in stable patients, 7-8 in cirrhosis)
   • Correct coagulopathy if INR >2.5 (FFP or PCC)
   • Platelets if <50,000

2. Risk Stratification: Glasgow-Blatchford Score

3. Medications:

   • Proton pump inhibitor IV (pantoprazole 80mg bolus → 8mg/h infusion)
   • Octreotide 50 mcg bolus → 50 mcg/h infusion (if variceal bleeding suspected)
   • Antibiotics (ceftriaxone 1g) in cirrhotic patients
   • Erythromycin 250mg IV 30-60 min before endoscopy (prokinetic, improves visualization)

4. Endoscopy: Within 24 hours (or within 12h if high-risk)

If Variceal Bleeding Confirmed:

• Endoscopic variceal ligation (EVL) preferred over sclerotherapy
• Continue octreotide × 2-5 days
• Start non-selective β-blocker (propranolol or carvedilol) for secondary prophylaxis
• Consider TIPS if refractory

If Non-Variceal Bleeding (peptic ulcer):

• Forrest Classification guides therapy
• High-risk stigmata (active bleeding, visible vessel, adherent clot) → endoscopic therapy
• PPI infusion × 72 hours, then oral PPI
• 8. pylori testing and eradication if positive

Key Takeaway: In cirrhotic patients with GI bleeding, always give antibiotics (reduces mortality) and octreotide empirically before endoscopy. Avoid over-transfusion (target Hgb 7-8) as it may increase rebleeding risk.

Common Mistakes to Avoid ⚠️

Cardiovascular

• ❌ Giving β-blockers in acute decompensated heart failure before volume optimization
• ❌ Missing posterior MI (isolated ST depression V1-V3 without checking posterior leads)
• ❌ Using NSAIDs in patients with heart failure (causes fluid retention, worsens HF)

Pulmonary

• ❌ Over-oxygenating COPD patients (target 88-92%, not 100%)
• ❌ Using D-dimer in high-probability PE patients (proceed directly to CTPA)
• ❌ Stopping steroids too early in COPD exacerbation (minimum 5 days)

Gastroenterology

• ❌ Delaying endoscopy in high-risk GI bleed (should be within 12-24 hours)
• ❌ Performing paracentesis through cellulitis or surgical scars
• ❌ Not giving albumin with large-volume paracentesis (>5L requires 6-8g albumin per liter removed)

Endocrinology

• ❌ Stopping insulin infusion when glucose normalizes in DKA (keep going until anion gap closes!)
• ❌ Correcting hyperglycemia too quickly in HHS (increased risk of cerebral edema)
• ❌ Starting β-blocker before α-blocker in pheochromocytoma (causes unopposed α-stimulation)

Nephrology

• ❌ Missing postrenal AKI by not checking bladder scan/Foley catheter
• ❌ Using FeNa in patients on diuretics (use FeUrea instead)
• ❌ Continuing metformin with eGFR <30 (lactic acidosis risk)

Infectious Disease

• ❌ Treating asymptomatic bacteriuria (except in pregnancy or pre-procedure)
• ❌ Not covering atypicals in pneumonia (always add macrolide or use respiratory fluoroquinolone)
• ❌ Forgetting to check HIV status in pneumonia patients (affects empiric coverage)

General

• ❌ Ordering "pan-cultures" in stable patients without clear infection source
• ❌ Using sliding scale insulin alone (always need basal insulin too)
• ❌ Not reconciling medications on admission and discharge

Key Takeaways 🎯

📚 Further Study

For deeper exploration of internal medicine topics:

1. UpToDate (www.uptodate.com) - Evidence-based clinical decision support; gold standard for point-of-care information

2. MKSAP (Medical Knowledge Self-Assessment Program) (www.acponline.org/mksap) - American College of Physicians' comprehensive internal medicine review; excellent board preparation

3. The Curbsiders Podcast (thecurbsiders.com) - Free internal medicine podcast with clinical pearls and evidence reviews; great for auditory learners during commutes

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Remember: Internal medicine is about systematic thinking and evidence-based decision making. Master the common presentations, understand the diagnostic algorithms, and know the first-line treatments. Your clinical rotations are where knowledge becomes wisdom—see patients, ask questions, and always think about the "why" behind management decisions. Good luck! 🩺✨