Differential for PE
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Here is a structured differential for pulmonary embolism, synthesized from Braunwald's Heart Disease, Goldman-Cecil Medicine, and Fuster & Hurst's The Heart:
Differential Diagnosis of Pulmonary Embolism
PE classically presents with acute dyspnea, pleuritic chest pain, tachycardia, and hypoxia. The conditions below can mimic one or more of these features.
Cardiovascular (Life-Threatening - Rule Out First)
| Condition | Key Distinguishing Features |
|---|---|
| Acute Coronary Syndrome (ACS/MI) | Crushing substernal chest pain, diaphoresis, ST changes on ECG, troponin rise; but note PE can also raise troponin via RV strain |
| Aortic Dissection | Tearing/ripping pain radiating to the back, pulse differentials between arms, widened mediastinum on CXR, aortic regurgitation murmur |
| Acute Decompensated Heart Failure | Orthopnea, PND, bilateral crackles, elevated BNP, cardiomegaly on CXR, peripheral edema |
| Pericarditis / Pericardial Disease | Pleuritic chest pain relieved by leaning forward, friction rub, diffuse saddle-shaped ST elevation on ECG |
| Pulmonary Hypertension | Chronic course, right heart failure signs (JVD, RV heave), progressive dyspnea on exertion |
Pulmonary
| Condition | Key Distinguishing Features |
|---|---|
| Pneumonia | Fever, productive cough, consolidation on CXR, leukocytosis - most common mimic |
| Pneumothorax | Sudden onset dyspnea, absent breath sounds unilaterally, hypoxia, visible on CXR |
| COPD/Asthma Exacerbation | Wheezing, prolonged expiratory phase, history of obstructive disease, response to bronchodilators |
| Acute Bronchitis | Cough-predominant, no hypoxia typically, no pleuritic pain |
| Pleuritis | Can occur with connective tissue disease, viral illness; friction rub, pleuritic pain without clot |
| Intrathoracic Malignancy | Subacute course, hemoptysis, weight loss, mass on imaging - note: malignancy is also a PE risk factor |
Musculoskeletal
| Condition | Key Distinguishing Features |
|---|---|
| Musculoskeletal/Costochondral Pain | Reproducible tenderness on palpation, worsened by movement - note that pulmonary infarction in PE can also cause chest wall tenderness |
| Rib Fracture | Trauma history, point tenderness, visible on CT |
Other
| Condition | Key Distinguishing Features |
|---|---|
| Anxiety/Panic Attack | Hyperventilation, no hypoxia, normal work-up - but always a diagnosis of exclusion |
| Hepatobiliary/Splenic Pathology | Right-sided pleuritic pain can mimic; look for right upper quadrant tenderness, LFT abnormalities |
Key Differentiating Tools
- ECG: Rules out ACS/pericarditis; PE may show S1Q3T3, sinus tachycardia, or T-wave inversions V1-V4 (right heart strain) - but the most common ECG finding in PE is simply sinus tachycardia or a normal tracing
- CXR: Usually near-normal in PE (a key clue); Westermark sign (focal oligemia) or Hampton's hump (peripheral wedge opacity) favor PE; lobar consolidation favors pneumonia; visible pneumothorax rules it in
- D-dimer: High sensitivity but low specificity - if negative with low/intermediate pretest probability (Wells or Geneva score), effectively excludes PE
- CTPA: Definitive test for PE; also identifies pneumonia, dissection, malignancy
- Troponin/BNP: Elevated in PE due to RV strain - can overlap with ACS and heart failure; use in context
Sources: Braunwald's Heart Disease, Table 87.5; Goldman-Cecil Medicine, Ch. 68; Fuster and Hurst's The Heart, Ch. 58
Most common cause of AKI
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Here is a comprehensive breakdown, synthesized from Goldman-Cecil Medicine, Harrison's Principles (22nd ed.), and Brenner & Rector's The Kidney:
Most Common Causes of AKI
AKI is classified into three anatomic categories. The relative frequency depends heavily on the clinical setting (community vs. hospital vs. ICU).
1. Prerenal Azotemia - Most Common Overall
~40-55% of all AKI cases; up to 60-70% of community-acquired AKI
Caused by reduced renal perfusion without intrinsic kidney damage. Kidney function normalizes within hours of restoring perfusion.
Causes:
- True volume depletion: vomiting, diarrhea, hemorrhage, burns, excessive diuresis, poor oral intake
- Effective volume depletion (normal or increased total body water, but reduced arterial flow to kidneys):
- Heart failure
- Liver failure / cirrhosis (most common AKI type in cirrhosis at 68% of cases)
- Nephrotic syndrome
- Medications reducing glomerular perfusion: NSAIDs, ACE inhibitors, ARBs, cyclosporine, contrast agents
2. Intrinsic AKI
~5-6% of ED admissions; up to 60% of ICU patients
Most Common Intrinsic Cause: Acute Tubular Necrosis (ATN)
The three drivers of ATN:
| Cause | Details |
|---|---|
| Ischemia | Prolonged prerenal azotemia, hypotension, shock - tubular epithelial cells die when perfusion is severely impaired |
| Sepsis | Complicates >50% of severe sepsis cases; can cause AKI even without overt hypotension; mechanism involves cytokine-mediated vasodilation, endothelial damage, and mitochondrial dysfunction - frank tubular necrosis is not always present despite the name |
| Nephrotoxins | - Extrinsic: iodinated contrast, aminoglycosides, vancomycin, cisplatin, NSAIDs - Intrinsic: myoglobin (rhabdomyolysis), hemoglobin (hemolysis), uric acid crystals (tumor lysis syndrome) |
Other intrinsic causes (less common):
- Acute Interstitial Nephritis (AIN): drug-induced (antibiotics, NSAIDs, PPIs) - second most common cause of AKI per Robbins
- Glomerulonephritis: rapidly progressive GN, IgA nephropathy
- Vascular: renal artery/vein thrombosis, atheroembolic disease, TTP/HUS, malignant hypertension
Harrison's note (2025): Although ATN is the classic label, human biopsy data often lacks frank necrosis in sepsis and ischemia cases - inflammation, apoptosis, and altered microvascular perfusion may be the dominant mechanisms.
3. Postrenal (Obstructive) AKI - Least Common
Requires bilateral obstruction or obstruction of a solitary kidney.
Most common causes:
- BPH (prostatic obstruction) - leading cause in older men
- Bilateral ureteral calculi
- Genitourinary malignancy
- Neurogenic bladder / anticholinergic drugs
- Retroperitoneal fibrosis
- Blood clots, sloughed renal papillae (papillary necrosis)
Summary by Setting
| Setting | Most Common Cause |
|---|---|
| Community-acquired | Prerenal azotemia (60-70%) |
| Hospital-acquired | Prerenal (~40%), then ATN |
| ICU | ATN from sepsis/ischemia (up to 60% have intrinsic AKI) |
| Cirrhosis | Prerenal (68%), then ATN (32%) |
| Older men | Postrenal from BPH |
| Pediatric | Prerenal (impaired perfusion) |
Sources: Goldman-Cecil Medicine, Ch. 106; Harrison's Principles of Internal Medicine 22e, Ch. 321; Brenner & Rector's The Kidney, Ch. 29
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