Causes and disease associations of chronic inflammation
THE CONTEXT
Chronic inflammation can arise from persistent infection, inappropriate immune responses, or prolonged exposure to harmful substances.
Persistent infections
•
Microorganisms that are difficult to eradicate, including mycobacteria and certain viruses, fungi, and parasites, can cause chronic inflammation.
•
An incompletely resolved acute infection may become chronic; an acute bacterial lung infection can progress to a chronic lung abscess.
Hypersensitivity diseases
•
Excessive and inappropriate immune activation causes chronic inflammation in hypersensitivity diseases.
•
In autoimmune diseases, autoantigens sustain immune reactions that produce chronic tissue damage and inflammation. Examples include rheumatoid arthritis and multiple sclerosis.
•
In allergic diseases, excessive responses to common environmental substances cause chronic inflammation, as in bronchial asthma.
•
Repeated inflammatory episodes can produce mixed acute and chronic morphologic patterns. Fibrosis may dominate the late stages.
Prolonged exposure to toxic agents
•
Both exogenous and endogenous agents can sustain chronic inflammation.
•
Prolonged inhalation of particulate silica, a nondegradable exogenous mineral, causes the inflammatory lung disease silicosis.
•
Atherosclerosis is a chronic inflammatory process of the arterial wall, induced partly by excessive production and tissue deposition of endogenous cholesterol and other lipids.
Additional disease associations
•
Some forms of chronic inflammation may contribute to diseases not conventionally considered inflammatory, including Alzheimer disease, metabolic syndrome, and associated type 2 diabetes.
Illustrated ulcer morphology
•
The illustrated chronic duodenal ulcer has a crater with inflammatory exudate at its base.