Pneumonia & Pleural Effusion: Step 1 review notes and self-test
Notes for the Pneumonia & Pleural Effusion rapid review: the clue that separates each of its 4 confusion pairs, with timestamps and a self-test.
October 21, 2026
This video covers pneumonia patterns, atypical pneumonia causes, pulmonary embolism, pleural effusions, and Light's criteria. Watch the video, then use these notes to test yourself on the clue that separates each pair.
Lobar / bronchopneumonia vs Atypical pneumonia
You separate these patterns by describing the image first. Lobar pneumonia causes dense, confluent consolidation in one lobe, bronchopneumonia causes patchy airway-centered consolidations, and atypical pneumonia causes a subacute walking illness with systemic symptoms and interstitial or patchy infiltrates. The trap is that both bronchopneumonia and atypical pneumonia can look patchy, so use toxicity, sputum, and the airway-centered versus interstitial pattern.
Lobar / bronchopneumonia vs Atypical pneumonia Lobar is one confluent lobe; bronchopneumonia is patchy airway-centered; atypical is interstitial/walking with systemic symptoms. Open the comparison and video →Mycoplasma / Chlamydia pneumoniae vs Legionella / viral pneumonia
Cold agglutinins and a young adult in a dorm or military outbreak point you toward Mycoplasma, while chronic mild cough with hoarseness or pharyngitis points toward Chlamydia pneumoniae. Contaminated water exposure with diarrhea, confusion, hyponatremia, and elevated liver enzymes points toward Legionella, while a preceding viral prodrome during flu or RSV season points toward viral pneumonia. The trap is that all four can cause atypical pneumonia with patchy interstitial infiltrates and only modest leukocytosis. Chest imaging does not decide, so pair the lung findings with the extra-pulmonary clue.
Mycoplasma / Chlamydia pneumoniae vs Legionella / viral pneumonia Cold agglutinins and young crowding point Mycoplasma; water exposure plus GI-neuro-hyponatremia points Legionella; viral prodrome points viral pneumonia. Open the comparison and video →Pneumonia vs Pulmonary embolism
Pneumonia builds over days with fever, productive cough, focal crackles, leukocytosis, and an infiltrate matched to the hypoxemia. Pulmonary embolism begins suddenly within minutes to hours with pleuritic chest pain, dyspnea, tachycardia, hypoxemia, relatively clear lungs, and clot risk factors. The trap is that both can cause tachypnea, hypoxemia, pleuritic chest pain, and infiltrates, so focus on gradual infection versus sudden onset with disproportionate hypoxemia and clot risk.
Pneumonia vs Pulmonary embolism Pneumonia is infectious alveolar filling; PE is sudden vascular obstruction with risk factors. Open the comparison and video →Transudate vs Exudate
Transudate is pressure-driven, low-protein, low-LDH fluid, while exudate is permeability-driven, protein-rich inflammatory fluid. Apply Light's criteria to pleural fluid because any one of these makes it an exudate: a pleural protein to serum protein ratio above 0.5, a pleural LDH to serum LDH ratio above 0.6, or pleural LDH above two-thirds of the upper normal serum LDH. If all three are below the cutoffs, the fluid is a transudate. The trap is that Light's criteria may falsely label fluid from a diuresed heart failure patient as exudative, and a serum-to-pleural-fluid albumin gradient above 1.2 g/dL reclassifies it as transudative.
Transudate vs Exudate Transudate is pressure-driven low-protein fluid; exudate is permeability-driven protein-rich inflammatory fluid. Open the comparison and video →Quick self-test
Name the diagnosis from the clue, then tap to check.
____ is protein-rich inflammatory fluid from increased vascular permeability or impaired lymph drainage, such as infection, malignancy, or autoimmune inflammation.
Exudate · Transudate vs Exudate
Subacute “walking” pattern with dry cough, headache, myalgias, less toxic appearance, and interstitial or patchy infiltrates rather than classic dense lobar consolidation.
Atypical pneumonia · Lobar / bronchopneumonia vs Atypical pneumonia
Fever, productive cough, focal crackles, and infiltrate on chest imaging.
Pneumonia · Pneumonia vs Pulmonary embolism
Sudden pleuritic chest pain, dyspnea, tachycardia, hypoxemia, clear lungs, and clot risk factors.
Pulmonary embolism · Pneumonia vs Pulmonary embolism
____ is low-protein, low-LDH fluid from hydrostatic or oncotic pressure imbalance, such as heart failure, cirrhosis, or nephrotic syndrome.
Transudate · Transudate vs Exudate
Keep going
Every pair in this review has a free page in the library with a side-by-side comparison and a practice question. Work through the ones you missed in the self-test first.