Neutrophils and exudate in acute; lymphocytes, macrophages and fibrosis in chronic
Mnemonic
“Acute is neutrophils and exudate; chronic is lymphocytes and repair”:
| Acute | Chronic | |
|---|---|---|
| Onset | Minutes to hours | Days to years |
| Cells | Neutrophils | Lymphocytes, plasma cells, macrophages |
| Vascular | Vasodilatation and exudate | Angiogenesis |
| Tissue | Usually resolves | Fibrosis and scarring |
| Signs | The cardinal signs | Often few |
The key difference is that in chronic inflammation destruction and repair proceed simultaneously, which is why it produces fibrosis rather than resolution.
Four outcomes of acute inflammation: resolution, suppuration (abscess), organisation (fibrosis), or progression to chronic.
Chronic inflammation can occur without a preceding acute phase, as in tuberculosis, rheumatoid arthritis and Crohn’s disease, which is a point often missed.
Granulomatous inflammation is a special form of chronic inflammation, in which epithelioid macrophages wall off a stimulus that cannot be eliminated.
Expansion
| Feature | Acute | Chronic |
|---|---|---|
| Onset | Minutes to hours | Days to years |
| Dominant cell | Neutrophil | Lymphocyte, plasma cell, macrophage |
| Vascular change | Marked, with exudate | Less prominent |
| Tissue change | Usually reversible | Fibrosis and tissue destruction |
| Systemic signs | Fever, neutrophilia, raised CRP | Weight loss, anaemia, raised ESR |
Outcomes of acute inflammation
- Complete resolution, if the tissue can regenerate and the stimulus is removed
- Abscess formation
- Healing by fibrosis (scarring), if damage is extensive or the tissue cannot regenerate
- Progression to chronic inflammation
Chronic inflammation arises either following acute inflammation that fails to resolve, or de novo as in autoimmune disease, persistent infection such as tuberculosis, and prolonged exposure to an irritant such as silica.
The simultaneous presence of destruction and repair is what distinguishes chronic inflammation morphologically, and it is why chronic inflammation causes progressive organ damage: fibrosis and loss of function accumulate even while the process continues.