What is Tuberculosis :

Tuberculosis is chronic communicable , granulomatous disease caused by myocobacterium tuberculosis.

Factor increasing the risk of TB :

Patient -related :

Age ( children >young adults <elderly).
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 :

Mycobacterium tuberculosis
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.