Page 163 - Textbook of Pathology, 6th Edition

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Figure 6.17 Fate of acute inflammation. CHAPTER 6

CHRONIC INFLAMMATION response to stimuli such as cytokines (lymphokines) and
bacterial endotoxins. On activation, macrophages release
DEFINITION AND CAUSES. Chronic inflammation is several biologically active substances e.g. acid and neutral
defined as prolonged process in which tissue destruction and proteases, oxygen-derived reactive metabolites and
inflammation occur at the same time. cytokines. These products bring about tissue destruction, Inflammation and Healing
Chronic inflammation can be caused by one of the neovascularisation and fibrosis.
following 3 ways: Other chronic inflammatory cells include lymphocytes,
1. Chronic inflammation following acute inflammation. plasma cells, eosinophils and mast cells. In chronic inflam-
When the tissue destruction is extensive, or the bacteria mation, lymphocytes and macrophages influence each other
survive and persist in small numbers at the site of acute and release mediators of inflammation.
inflammation e.g. in osteomyelitis, pneumonia terminating 2. TISSUE DESTRUCTION OR NECROSIS. Tissue
in lung abscess.
destruction and necrosis are central features of most forms
2. Recurrent attacks of acute inflammation. When of chronic inflammatory lesions. This is brought about by
repeated bouts of acute inflammation culminate in activated macrophages which release a variety of biologi-
chronicity of the process e.g. in recurrent urinary tract cally active substances e.g. protease, elastase, collagenase,
infection leading to chronic pyelonephritis, repeated acute lipase, reactive oxygen radicals, cytokines (IL-1, IL-8,
infection of gallbladder leading to chronic cholecystitis. TNF-α), nitric oxide, angiogenesis growth factor etc.
3. Chronic inflammation starting de novo. When the infec- 3. PROLIFERATIVE CHANGES. As a result of necrosis,
tion with organisms of low pathogenicity is chronic from the proliferation of small blood vessels and fibroblasts is
beginning e.g. infection with Mycobacterium tuberculosis. stimulated resulting in formation of inflammatory
granulation tissue. Eventually, healing by fibrosis and
GENERAL FEATURES OF CHRONIC INFLAMMATION collagen laying takes place.

Though there may be differences in chronic inflammatory SYSTEMIC EFFECTS OF CHRONIC INFLAMMATION
response depending upon the tissue involved and causative
organisms, there are some basic similarities amongst various Chronic inflammation is associated with following systemic
types of chronic inflammation. Following general features features:
characterise any chronic inflammation:
1. Fever. Invariably there is mild fever, often with loss of
1. MONONUCLEAR CELL INFILTRATION. Chronic weight and weakness.
inflammatory lesions are infiltrated by mononuclear
inflammatory cells like phagocytes and lymphoid cells. 2. Anaemia. As discussed in Chapter 12, chronic inflam-
Phagocytes are represented by circulating monocytes, tissue mation is accompanied by anaemia of varying degree.
macrophages, epithelioid cells and sometimes, 3. Leucocytosis. As in acute inflammation, chronic
multinucleated giant cells. The macrophages comprise the inflammation also has leucocytosis but generally there is
most important cells in chronic inflammation. These may relative lymphocytosis in these cases.
appear at the site of chronic inflammation from:
i) chemotactic factors and adhesion molecules for continued 4. ESR. ESR is elevated in all cases of chronic inflammation.
infiltration of macrophages; 5. Amyloidosis. Long-term cases of chronic suppurative
ii) local proliferation of macrophages; and inflammation may develop secondary systemic (AA)
iii) longer survival of macrophages at the site of inflam- amyloidosis.
mation.
TYPES OF CHRONIC INFLAMMATION
The blood monocytes on reaching the extravascular space
transform into tissue macrophages. Besides the role of Conventionally, chronic inflammation is subdivided into 2
macrophages in phagocytosis, they may get activated in types: