Resp lect 2TB.pdf

Pathology of Tuberculosis By Dr.Nugdalla Abdel Rahman  Introduction  It is a communicable chronic granulomatous disease mostly caused by Mycobacterium tuberculosis ( by air) and rarely caused by Mycobacterium bovis ( by milk)  Usually involve the lung, but can involve a...

Pathology of Tuberculosis By Dr.Nugdalla Abdel Rahman  Introduction  It is a communicable chronic granulomatous disease mostly caused by Mycobacterium tuberculosis ( by air) and rarely caused by Mycobacterium bovis ( by milk)  Usually involve the lung, but can involve any other organ of the body.  Microbiology of TB:  TB Mostly caused by Mycobacterium  It is aerobic, no toxins, no spore -forming, non motile Bacteria ,has Mycolic acid in it’s bacterial wall.Mycobacterium avium and intracellulare causes atypical tuberculosis in patient with AIDs  Has ability to escape host defense mechanisms  5-200 inhaled bacilli are usually necessary for infection to develop  RISK GROUP  The risk of infection is increased in small enclosed areas and in areas with poor ventilation  homeless individuals,  malnourished individuals,  those living in crowded areas  Steroid therapy, cancer chemotherapy, and hematologic malignancies  Stages of the disease  Stage 1  Exposure with recent contact - history with a person who has contagious TB  No physical signs or symptoms and has a negative test result  Note that in some patients it takes 3 months for the test result to become positive ochildren younger than 5 years may develop disseminated TB in the form of miliary disease or tubercular meningitis before the test result becomes positive. Thus, a very high index of suspicion is required when a young patient has a history of contact.  Stage 2 o Positive TST result. o No signs and symptoms occur, o incidental CXR may show the primary complex  Stage 3 o Appearance of signs and symptoms depending on the location of the disease. o Radiographic abnormalities also may be seen  Stage 4  No clinical findings suggesting current disease are present.  This implies that the patient has a history of previous episodes of TB  stable radiographic findings with a significant reaction to the TST and negative bacteriologic studies.  Pathogenesis  A cell-mediated immune (CMI) response terminates the growth of the M tuberculosis for 2-3 weeks after initial infection  Not all infected with M tuberculosis develop active disease  In individuals who are immunocompetent, the lifetime risk of developing disease is 5-10%  Pathogenesis of TB: Type IV hypersensitivity - Granuloma Caseating granuloma Escape killing by macrophages because has Mycolic acid wax coat TB granuloma Pathogenesis  Bacterial entry  T Lymphocytes.  Macrophages.  Epitheloid cells.  Proliferation.  Central Necrosis.  Giant cell formation.  Fibrosis.  Morphology of Granuloma 1. Rounded tight collection of chronic inflammatory cells. 2. Central Caseous necrosis. 3. Active macrophages - epithelioid cells. 4. Outer layer of lymphocytes & fibroblasts. 5. Langhans giant cells – joined epithelioid cells.  A Tuberculous Granuloma  The initial lesion is a small focus of consolidation of