Purulent
Summary
Purulent means containing or producing pus, an exudate of dead neutrophils, liquefied tissue debris, and often bacteria. Purulent inflammation is the hallmark of pyogenic bacterial infection.
Detail
Pus forms when neutrophils recruited to a site of infection degranulate and undergo necrosis, releasing lysosomal enzymes that liquefy surrounding tissue. Classic pyogenic organisms include Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Neisseria species, and many gram-negative rods. A walled-off collection of pus is an abscess, and the governing clinical principle is that an abscess requires drainage, since antibiotics penetrate poorly into an avascular, acidic, enzyme-rich cavity. Purulent exudate is distinguished from serous exudate (thin, protein-poor, as in a blister), fibrinous exudate (rich in fibrin, as in fibrinous pericarditis producing a friction rub), and haemorrhagic exudate. The distinction matters clinically: in a red eye, purulent discharge suggests bacterial conjunctivitis while watery discharge suggests viral, and in COPD increased sputum purulence is one of the Anthonisen criteria used to decide on antibiotics for an exacerbation.
Sources
- Robbins Basic Pathology
- First Aid for the USMLE Step 1
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