Page 165 - Textbook of Pathology, 6th Edition

staining abundant cytoplasm with hazy outlines so that the EXAMPLES OF GRANULOMATOUS 149
cell membrane of adjacent epithelioid cells is closely apposed.
Epithelioid cells are weakly phagocytic. INFLAMMATION
2. Multinucleate giant cells. Multinucleate giant cells are Granulomatous inflammation is typical of reaction to poorly
formed by fusion of adjacent epithelioid cells and may have digestible agents elicited by tuberculosis, leprosy, fungal
20 or more nuclei. These nuclei may be arranged at the infections, schistosomiasis, foreign particles etc. A CHAPTER 6
periphery like horseshoe or ring, or are clustered at the two comprehensive list of important examples of granulomatous
poles (Langhans’ giant cells), or they may be present centrally conditions, their etiologic agents and salient features is given
(foreign body giant cells). The former are commonly seen in in Table 6.4. The principal examples (marked with asterisk
tuberculosis while the latter are common in foreign body in the table) are discussed below while a few others appear
tissue reactions. Like epithelioid cells, these giant cells are in relevant Chapters later.
weakly phagocytic but produce secretory products which
help in removing the invading agents. TUBERCULOSIS
3. Lymphoid cells. As a cell mediated immune reaction to Tissue response in tuberculosis represents classical example
antigen, the host response by lymphocytes is integral to of chronic granulomatous inflammation in humans.
composition of a granuloma. Plasma cells indicative of
accelerated humoral immune response are present in some CAUSATIVE ORGANISM. Tubercle bacillus or Koch’s Inflammation and Healing
types of granulomas. bacillus (named after discovery of the organism by Robert
4. Necrosis. Necrosis may be a feature of some granulo- Koch in 1882) called Mycobacterium tuberculosis causes
matous conditions e.g. central caseation necrosis of tuberculosis in the lungs and other tissues of the human body.
tuberculosis, so called because of cheese-like appearance and The organism is a strict aerobe and thrives best in tissues with
consistency of necrosis. high oxygen tension such as in the apex of the lung.
Out of various pathogenic strains for human disease
5. Fibrosis. Fibrosis is a feature of healing by proliferating included in Mycobacterium tuberculosis complex, currently
fibroblasts at the periphery of granuloma. most common is M. tuberculosis hominis (human strain), while
The classical example of granulomatous inflammation is M. tuberculosis bovis (bovine strain) used to be common
the tissue response to tubercle bacilli which is called tubercle pathogen to human beings during the era of consumption of
seen in tuberculosis (described below). A fully-developed unpasteurised milk but presently constitutes a small number
tubercle is about 1 mm in diameter with central area of of human cases. Other less common strains included in the
caseation necrosis, surrounded by epithelioid cells and one complex are M. africanum (isolated from patients from parts
to several multinucleated giant cells (commonly Langhans’ of Africa), M. microti, M. pinnipedii and M. canettii. A non-
type), surrounded at the periphery by lymphocytes and pathogenic strain, M. smegmatis, is found in the smegma and
bounded by fibroblasts and fibrous tissue (Fig. 6.19).
as contaminant in the urine of both men and women.
M. tuberculosis hominis is a slender rod-like bacillus,
0.5 μm by 3 μm, is neutral on Gram staining, and can be
demonstrated by the following methods:
1. Acid fast (Ziehl-Neelsen) staining. The acid fastness of the
tubercle bacilli is due to mycolic acids, cross-linked fatty acids
and other lipids in the cell wall of the organism making it
impermeable to the usual stains. It takes up stain by heated
carbol fuchsin and resists decolourisation by acids and
alcohols (acid fast and alcohol fast) and can be decolourised
by 20% sulphuric acid (compared to 5% sulphuric acid for
declourisation for M. leprae which are less acid fast) (Fig. 6.20).
False positive AFB staining is seen due to Nocardia,
Rhodococcus, Legionella, and some protozoa such as Isospora
and Cryptosporidium.
2. Fluorescent dye methods.
3. Culture of the organism from sputum in Lowenstein-
Jensen (L.J.) medium for 6 weeks.
4. Guinea pig inoculation method by subcutaneous injection
of the organisms.
5. Molecular methods such as PCR are the most recent
methods.
Figure 6.19 Morphology of a tubercle. There is central caseation ATYPICAL MYCOBACTERIA (NON-TUBERCULOUS
necrosis, surrounded by elongated epithelioid cells having characteristic
slipper-shaped nuclei, with interspersed Langhans’ giant cells. Periphery MYCOBACTERIA). The term atypical mycobacteria or non-
shows lymphocytes. tuberculous mycobacteria is used for mycobacterial species