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What is Tuberculosis :
Tuberculosis is chronic communicable , granulomatous disease caused by myocobacterium tuberculosis.
Factor increasing the risk of TB :
Patient -related :
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Age ( children >young adults <elderly).
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First generation immigrants from high-prevalence countries.
3.Close contacts of patients with smear- positive pulmonary tuberculosis.
4.Overcrowding :prisons, collective dormitories.
5.Chest radiographic evidence of self- healed tuberculosis .
- Primary infection<1 year previously.
Associated disease :
- Immunosuppression - HIV, infliximab, high- dose corticosteroids, cytotoxic agents.
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- Malignancy (especially lymphoma and leukaemia ).
3.Type 1 diabetes mellitus .
4.Chronic renal failure .
5.Silicosis .
6.Gastrointestinal disease associated with malnutrition ( gastrectomy, jejuno -ileal bypass , cancer of the pancreas, malabsorption ).
7.Deficiency of vitamin D or A.
Organisms responsible for tuberculosis :
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Mycobacterium tuberculosis
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Mycobacterium bovis
3.Mycobacterium africanum
Primary pulmonary TB :
Primary TB refers to the infection of a previously uninfected (tuberculin- negative ) individual .
Miliary TB :
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Blood- borne dissemination gives rise to miliary Tb which may present acutely but more frequently is characterised by 2-3 weeks of fever, night sweats , anorexia , weight loss and dry cough .
the classical appearances on chest X- ray are those of fine 1- 2 mm lesions ( millet seed) distributed
throughout the lung fields, although occasionally the appearances are coarser.
Post- primary pulmonary TB :
Refers to the infection of previously infected (tuberculin- positive) individual .
Pathogenesis of pulmonary TB :
- M. bovis infection aries from drinking non - sterilised milk from infected cows ; otherwise ,M tuberculosis is spread by the inhalation of aerosolised droplet nuclei from other infected patients .
2.The smallest particles(1-5um) enter the periphery of the lung and are engulfed by macrophage.
3.In response to antigen presentation, CD4+ T lymphocytes produce an array of cytokines, including interferon - gamma (IFN-gama) that drive the recruitment of monocytes and direct the formation of granulomas limiting the replication and spread of the organism.
4.Classical tuberculosis granulomas display central caseous necrosis.
5.The formation of a mass of granulomas surrounding an area of caseation leads to the appearance of the primary lesion in the lung, referred to as the Ghons focus.
6.The combination of a primary lesion and regional lymph node involvement is termed the Ghons complex .
7.If the bacilli spread (either by lymph or blood ) before immunity is established, secondary foci may be established in other organs including lymph nodes, serous membranes , bones, liver , kidney, and lung.
Symptoms of TB:
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- Chronic cough , often with haemoptysis.
2.Pyrexia of unknown regions.
3.Evening rise of temperature.
4, Night sweats.
5.Anorexia.
6.Weight loss.
7.Unresolved pneumonia .
8.May be asymptomatic ( diagnosis on chest X-ray)
Signs :
- Raised temperature .
2.Patient may be cachectic .
- Cervical and other lymphadenopathy- when disseminated.
4.Ausculatation of chest is frequently normal .
5.Features of pleural effusion may be found .
6.Features of pneumothorax may be found .
- In advanced disease , widespread ceackles may be found .
Investigation :
- CBC, ESR and HB% : High rise of ESR , lymphocytosis, anaemia .
2.Chest X-ray : Patchy opacity.
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3.Sputum or bronchoalveolar lavage for AFB : May be found by Ziehl- Neelsen staining.
4.PCR :Nucleic acid amplification.
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Culture
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Tuberculin test: Useful only primary or deep - seated infection.
